Table of Contents
- Developing Applications With Open MCT
- Scope and purpose of this document
- Building From Source
- Starting an Open MCT application
- Types
- Plugins
- Domain Objects and Identifiers
- Root Objects
- Object Providers
- Composition Providers
- Telemetry API
- Time API
- Indicators
- Priority API
This document is intended to serve as a reference for developing an application based on Open MCT. It will provide details of the API functions necessary to extend the Open MCT platform meet common use cases such as integrating with a telemetry source.
The best place to start is with the Open MCT Tutorials. These will walk you through the process of getting up and running with Open MCT, as well as addressing some common developer use cases.
The latest version of Open MCT is available from our GitHub repository.
If you have git
, and node
installed, you can build Open MCT with the commands
git clone https://github.com/nasa/openmct.git
cd openmct
npm install
These commands will fetch the Open MCT source from our GitHub repository, and
build a minified version that can be included in your application. The output
of the build process is placed in a dist
folder under the openmct source
directory, which can be copied out to another location as needed. The contents
of this folder will include a minified javascript file named openmct.js
as
well as assets such as html, css, and images necessary for the UI.
To start a minimally functional Open MCT application, it is necessary to
include the Open MCT distributable, enable some basic plugins, and bootstrap
the application. The tutorials walk through the process of getting Open MCT up
and running from scratch, but provided below is a minimal HTML template that
includes Open MCT, installs some basic plugins, and bootstraps the application.
It assumes that Open MCT is installed under an openmct
subdirectory, as
described in Building From Source.
This approach includes openmct using a simple script tag, resulting in a global
variable named openmct
. This openmct
object is used subsequently to make
API calls.
Open MCT is packaged as a UMD (Universal Module Definition) module, so common script loaders are also supported.
<!DOCTYPE html>
<html>
<head>
<title>Open MCT</title>
<script src="dist/openmct.js"></script>
</head>
<body>
<script>
openmct.install(openmct.plugins.LocalStorage());
openmct.install(openmct.plugins.MyItems());
openmct.install(openmct.plugins.UTCTimeSystem());
openmct.start();
</script>
</body>
</html>
The Open MCT library included above requires certain assets such as html templates, images, and css. If you installed Open MCT from GitHub as described in the section on Building from Source then these assets will have been downloaded along with the Open MCT javascript library.
There are some plugins bundled with the application that provide UI, persistence, and other default configuration which are necessary to be able to do anything with the application initially. Any of these plugins can, in principle, be replaced with a custom plugin. The included plugins are documented in the Included Plugins section.
The Open MCT library includes its own TypeScript declaration files which can be used to provide code hints and typechecking in your own Open MCT application.
Open MCT's type declarations are generated via tsc
from JSDoc-style comment
blocks. For more information on this, check out TypeScript's documentation.
In order to use Open MCT's provided types in your own application, create a
jsconfig.js
at the root of your project with this minimal configuration:
{
"compilerOptions": {
"baseUrl": "./",
"target": "es6",
"checkJs": true,
"moduleResolution": "node",
"paths": {
"openmct": ["node_modules/openmct/dist/openmct.d.ts"]
}
}
}
Then, simply import and use openmct
in your application:
import openmct from "openmct";
The effort to add types for Open MCT's public API is ongoing, and the provided type declarations may be incomplete.
If you would like to contribute types to Open MCT, please check out TypeScript's documentation on generating type declarations from JSDoc-style comment blocks. Then read through our contributing guide and open a PR!
openmct.install(function install(openmctAPI) {
// Do things here
// ...
});
New plugins are installed in Open MCT by calling openmct.install
, and
providing a plugin installation function. This function will be invoked on
application startup with one parameter - the openmct API object. A common
approach used in the Open MCT codebase is to define a plugin as a function that
returns this installation function. This allows configuration to be specified
when the plugin is included.
eg.
openmct.install(openmct.plugins.Elasticsearch("http://localhost:8002/openmct"));
This approach can be seen in all of the plugins provided with Open MCT.
Domain Objects are the basic entities that represent domain knowledge in Open MCT. The temperature sensor on a solar panel, an overlay plot comparing the results of all temperature sensors, the command dictionary for a spacecraft, the individual commands in that dictionary, the "My Items" folder: All of these things are domain objects.
A Domain Object is simply a javascript object with some standard attributes.
An example of a Domain Object is the "My Items" object which is a folder in
which a user can persist any objects that they create. The My Items object
looks like this:
{
identifier: {
namespace: ""
key: "mine"
}
name:"My Items",
type:"folder",
location:"ROOT",
composition: []
}
The main attributes to note are the identifier
, and type
attributes.
identifier
: A composite key that provides a universally unique identifier for this object. Thenamespace
andkey
are used to identify the object. Thekey
must be unique within the namespace.type
: All objects in Open MCT have a type. Types allow you to form an ontology of knowledge and provide an abstraction for grouping, visualizing, and interpreting data. Details on how to define a new object type are provided below.
Open MCT uses a number of builtin types. Typically you are going to want to define your own when extending Open MCT.
Custom types may be registered via the addType
function on the Open MCT Type
registry.
eg.
openmct.types.addType('example.my-type', {
name: "My Type",
description: "This is a type that I added!",
creatable: true
});
The addType
function accepts two arguments:
- A
string
key identifying the type. This key is used when specifying a type for an object. We recommend prefixing your types with a namespace to avoid conflicts with other plugins. - An object type specification. An object type definition supports the following
attributes
name
: astring
naming this object typedescription
: astring
specifying a longer-form description of this typeinitialize
: afunction
which initializes the model for new domain objects of this type. This can be used for setting default values on an object when it is instantiated.creatable
: Aboolean
indicating whether users should be allowed to create this type (default:false
). This will determine whether the type appears in theCreate
menu.cssClass
: Astring
specifying a CSS class to apply to each representation of this object. This is used for specifying an icon to appear next to each object of this type.
The Open MCT Tutorials provide a step-by-step examples of writing code for Open MCT that includes a section on defining a new object type.
In many cases, you'd like a certain object (or a certain hierarchy of objects) to be accessible from the top level of the application (the tree on the left-hand side of Open MCT.) For example, it is typical to expose a telemetry dictionary as a hierarchy of telemetry-providing domain objects in this fashion.
To do so, use the addRoot
method of the object API.
eg.
openmct.objects.addRoot({
namespace: "example.namespace",
key: "my-key"
},
openmct.priority.HIGH);
The addRoot
function takes a two arguments, the first can be an object identifier for a root level object, or an array of identifiers for root
level objects, or a function that returns a promise for an identifier or an array of root level objects, the second is a priority or numeric value.
When using the getAll
method of the object API, they will be returned in order of priority.
eg.
openmct.objects.addRoot(identifier, openmct.priority.LOW); // low = -1000, will appear last in composition or tree
openmct.objects.addRoot(otherIdentifier, openmct.priority.HIGH); // high = 1000, will appear first in composition or tree
Root objects are loaded just like any other objects, i.e. via an object provider.
An Object Provider is used to build Domain Objects, typically retrieved from some source such as a persistence store or telemetry dictionary. In order to integrate telemetry from a new source an object provider will need to be created that can build objects representing telemetry points exposed by the telemetry source. The API call to define a new object provider is fairly straightforward. Here's a very simple example:
openmct.objects.addProvider('example.namespace', {
get: function (identifier) {
return Promise.resolve({
identifier: identifier,
name: 'Example Object',
type: 'example-object-type'
});
}
});
The addProvider
function takes two arguments:
namespace
: Astring
representing the namespace that this object provider will provide objects for.provider
: Anobject
with a single function,get
. This function accepts an Identifier for the object to be provided. It is expected that theget
function will return a Promise that resolves with the object being requested.
In future, object providers will support other methods to enable other operations with persistence stores, such as creating, updating, and deleting objects.
The composition of a domain object is the list of objects it contains, as shown (for example) in the tree for browsing. Open MCT provides a default solution for composition, but there may be cases where you want to provide the composition of a certain object (or type of object) dynamically.
You may want to populate a hierarchy under a custom root-level object based on the contents of a telemetry dictionary. To do this, you can add a new Composition Provider:
openmct.composition.addProvider({
appliesTo: function (domainObject) {
return domainObject.type === 'example.my-type';
},
load: function (domainObject) {
return Promise.resolve(myDomainObjects);
}
});
The addProvider
function accepts a Composition Provider object as its sole
argument. A Composition Provider is a javascript object exposing two functions:
appliesTo
: Afunction
that accepts adomainObject
argument, and returns aboolean
value indicating whether this composition provider applies to the given object.load
: Afunction
that accepts adomainObject
as an argument, and returns aPromise
that resolves with an array of Identifier. These identifiers will be used to fetch Domain Objects from an Object Provider
The default composition provider applies to any domain object with a
composition
property. The value of composition
should be an array of
identifiers, e.g.:
var domainObject = {
name: "My Object",
type: 'folder',
composition: [
{
id: '412229c3-922c-444b-8624-736d85516247',
namespace: 'foo'
},
{
key: 'd6e0ce02-5b85-4e55-8006-a8a505b64c75',
namespace: 'foo'
}
]
};
The Open MCT telemetry API provides two main sets of interfaces-- one for integrating telemetry data into Open MCT, and another for developing Open MCT visualization plugins utilizing the telemetry API.
The APIs for visualization plugins are still a work in progress and docs may change at any time. However, the APIs for integrating telemetry metadata into Open MCT are stable and documentation is included below.
There are two main tasks for integrating telemetry sources-- describing telemetry objects with relevant metadata, and then providing telemetry data for those objects. You'll use an Object Provider to provide objects with the necessary Telemetry Metadata, and then register a Telemetry Provider to retrieve telemetry data for those objects. Alternatively, you can register a telemetry metadata provider to provide the necessary telemetry metadata.
For a step-by-step guide to building a telemetry adapter, please see the Open MCT Tutorials.
A telemetry object is a domain object with a telemetry property. To take an example from the tutorial, here is the telemetry object for the "fuel" measurement of the spacecraft:
{
"identifier": {
"namespace": "example.taxonomy",
"key": "prop.fuel"
},
"name": "Fuel",
"type": "example.telemetry",
"telemetry": {
"values": [
{
"key": "value",
"name": "Value",
"unit": "kilograms",
"format": "float",
"min": 0,
"max": 100,
"hints": {
"range": 1
}
},
{
"key": "utc",
"source": "timestamp",
"name": "Timestamp",
"format": "utc",
"hints": {
"domain": 1
}
}
]
}
}
The most important part of the telemetry metadata is the values
property-- this describes the attributes of telemetry datums (objects) that a telemetry provider returns. These descriptions must be provided for telemetry views to work properly.
telemetry.values
is an array of value description objects, which have the following fields:
attribute | type | flags | notes |
---|---|---|---|
key |
string | required | unique identifier for this field. |
hints |
object | required | Hints allow views to intelligently select relevant attributes for display, and are required for most views to function. See section on "Value Hints" below. |
name |
string | optional | a human readable label for this field. If omitted, defaults to key . |
source |
string | optional | identifies the property of a datum where this value is stored. If omitted, defaults to key . |
format |
string | optional | a specific format identifier, mapping to a formatter. If omitted, uses a default formatter. For enumerations, use enum . For timestamps, use utc if you are using utc dates, otherwise use a key mapping to your custom date format. |
unit |
string | optional | the unit of this value, e.g. km , seconds , parsecs |
min |
number | optional | the minimum possible value of this measurement. Will be used by plots, gauges, etc to automatically set a min value. |
max |
number | optional | the maximum possible value of this measurement. Will be used by plots, gauges, etc to automatically set a max value. |
enumerations |
array | optional | for objects where format is "enum" , this array tracks all possible enumerations of the value. Each entry in this array is an object, with a value property that is the numerical value of the enumeration, and a string property that is the text value of the enumeration. ex: {"value": 0, "string": "OFF"} . If you use an enumerations array, min and max will be set automatically for you. |
Each telemetry value description has an object defining hints. Keys in this object represent the hint itself, and the value represents the weight of that hint. A lower weight means the hint has a higher priority. For example, multiple values could be hinted for use as the y-axis of a plot (raw, engineering), but the highest priority would be the default choice. Likewise, a table will use hints to determine the default order of columns.
Known hints:
domain
: Values with adomain
hint will be used for the x-axis of a plot, and tables will render columns for these values first.range
: Values with arange
hint will be used as the y-axis on a plot, and tables will render columns for these values after thedomain
values.image
: Indicates that the value may be interpreted as the URL to an image file, in which case appropriate views will be made available.imageDownloadName
: Indicates that the value may be interpreted as the name of the image file.
Open MCT provides a number of ways to pivot through data and link data via time. The Time Conductor helps synchronize multiple views around the same time.
In order for the time conductor to work, there will always be an active "time system". All telemetry metadata must have a telemetry value with a key
that matches the key
of the active time system. You can use the source
attribute on the value metadata to remap this to a different field in the telemetry datum-- especially useful if you are working with disparate datasources that have different field mappings.
Telemetry providers are responsible for providing historical and real-time telemetry data for telemetry objects. Each telemetry provider determines which objects it can provide telemetry for, and then must implement methods to provide telemetry for those objects.
A telemetry provider is a javascript object with up to four methods:
supportsSubscribe(domainObject, callback, options)
optional. Must be implemented to provide realtime telemetry. Should returntrue
if the provider supports subscriptions for the given domain object (and request options).subscribe(domainObject, callback, options)
required ifsupportsSubscribe
is implemented. Establish a subscription for realtime data for the given domain object. Should invokecallback
with a single telemetry datum every time data is received. Must return an unsubscribe function. Multiple views can subscribe to the same telemetry object, so it should always return a new unsubscribe function.supportsRequest(domainObject, options)
optional. Must be implemented to provide historical telemetry. Should returntrue
if the provider supports historical requests for the given domain object.request(domainObject, options)
required ifsupportsRequest
is implemented. Must return a promise for an array of telemetry datums that fulfills the request. Theoptions
argument will include astart
,end
, anddomain
attribute representing the query bounds. See Telemetry Requests and Responses for more info on how to respond to requests.supportsMetadata(domainObject)
optional. Implement and returntrue
for objects that you want to provide dynamic metadata for.getMetadata(domainObject)
required ifsupportsMetadata
is implemented. Must return a valid telemetry metadata definition that includes at least one valueMetadata definition.supportsLimits(domainObject)
optional. Implement and returntrue
for domain objects that you want to provide a limit evaluator for.getLimitEvaluator(domainObject)
required ifsupportsLimits
is implemented. Must return a valid LimitEvaluator for a given domain object.
Telemetry providers are registered by calling openmct.telemetry.addProvider(provider)
, e.g.
openmct.telemetry.addProvider({
supportsRequest: function (domainObject, options) { /*...*/ },
request: function (domainObject, options) { /*...*/ },
})
Note: it is not required to implement all of the methods on every provider. Depending on the complexity of your implementation, it may be helpful to instantiate and register your realtime, historical, and metadata providers separately.
Telemetry requests support time bounded queries. A call to a Telemetry Provider's request
function will include an options
argument. These are simply javascript objects with attributes for the request parameters. An example of a telemetry request object with a start and end time is included below:
{
start: 1487981997240,
end: 1487982897240,
domain: 'utc'
}
In this case, the domain
is the currently selected time-system, and the start and end dates are valid dates in that time system.
A telemetry provider's request
method should return a promise for an array of telemetry datums. These datums must be sorted by domain
in ascending order.
The telemetry provider's request
method will also return an object signal
with an aborted
property with a value true
if the request has been aborted by user navigation. This can be used to trigger actions when a request has been aborted.
To improve performance views may request a certain strategy for data reduction. These are intended to improve visualization performance by reducing the amount of data needed to be sent to the client. These strategies will be indicated by additional parameters in the request options. You may choose to handle them or ignore them.
Note: these strategies are currently being tested in core plugins and may change based on developer feedback.
This request is a "depth based" strategy. When a view is only capable of
displaying a single value (or perhaps the last ten values), then it can
use the latest
request strategy with a size
parameter that specifies
the number of results it desires. The size
parameter is a hint; views
must not assume the response will have the exact number of results requested.
example:
{
start: 1487981997240,
end: 1487982897240,
domain: 'utc',
strategy: 'latest',
size: 1
}
This strategy says "I want the latest data point in this time range". A provider which recognizes this request should return only one value-- the latest-- in the requested time range. Depending on your back-end implementation, performing these queries in bulk can be a large performance increase. These are generally issued by views that are only capable of displaying a single value and only need to show the latest value.
example:
{
start: 1487981997240,
end: 1487982897240,
domain: 'utc',
strategy: 'minmax',
size: 720
}
MinMax queries are issued by plots, and may be issued by other types as well. The aim is to reduce the amount of data returned but still faithfully represent the full extent of the data. In order to do this, the view calculates the maximum data resolution it can display (i.e. the number of horizontal pixels in a plot) and sends that as the size
. The response should include at least one minimum and one maximum value per point of resolution.
Telemetry format objects define how to interpret and display telemetry data. They have a simple structure:
key
: Astring
that uniquely identifies this formatter.format
: Afunction
that takes a raw telemetry value, and returns a human-readablestring
representation of that value. It has one required argument, and three optional arguments that provide context and can be used for returning scaled representations of a value. An example of this is representing time values in a scale such as the time conductor scale. There are multiple ways of representing a point in time, and by providing a minimum scale value, maximum scale value, and a count, it's possible to provide more useful representations of time given the provided limitations.value
: The raw telemetry value in its native type.minValue
: An optional argument specifying the minimum displayed value.maxValue
: An optional argument specifying the maximum displayed value.count
: An optional argument specifying the number of displayed values.
parse
: Afunction
that takes astring
representation of a telemetry value, and returns the value in its native type. Note parse might receive an already-parsed value. This function should be idempotent.validate
: Afunction
that takes astring
representation of a telemetry value, and returns aboolean
value indicating whether the provided string can be parsed.
Formats are registered with the Telemetry API using the addFormat
function. eg.
openmct.telemetry.addFormat({
key: 'number-to-string',
format: function (number) {
return number + '';
},
parse: function (text) {
return Number(text);
},
validate: function (text) {
return !isNaN(text);
}
});
A single telemetry point is considered a Datum, and is represented by a standard javascript object. Realtime subscriptions (obtained via subscribe) will invoke the supplied callback once for each telemetry datum recieved. Telemetry requests (obtained via request) will return a promise for an array of telemetry datums.
A telemetry datum is a simple javascript object, e.g.:
{
"timestamp": 1491267051538,
"value": 77,
"id": "prop.fuel"
}
The key-value pairs of this object are described by the telemetry metadata of a domain object, as discussed in the Telemetry Metadata section.
Limit evaluators allow a telemetry integrator to define which limits exist for a telemetry endpoint and how limits should be applied to telemetry from a given domain object.
A limit evaluator can implement the evalute
method which is used to define how limits
should be applied to telemetry and the getLimits
method which is used to specify
what the limit values are for different limit levels.
Limit levels can be mapped to one of 5 colors for visualization:
purple
, red
, orange
, yellow
and cyan
.
For an example of a limit evaluator, take a look at examples/generator/SinewaveLimitProvider.js
.
The APIs for requesting telemetry from Open MCT -- e.g. for use in custom views -- are currently in draft state and are being revised. If you'd like to experiment with them before they are finalized, please contact the team via the contact-us link on our website.
Open MCT provides API for managing the temporal state of the application. Central to this is the concept of "time bounds". Views in Open MCT will typically show telemetry data for some prescribed date range, and the Time API provides a way to centrally manage these bounds.
The Time API exposes a number of methods for querying and setting the temporal state of the application, and emits events to inform listeners when the state changes.
Because the data displayed tends to be time domain data, Open MCT must always
have at least one time system installed and activated. When you download Open
MCT, it will be pre-configured to use the UTC time system, which is installed and activated, along with other default plugins, in index.html
. Installing and activating a time system is simple, and is covered
in the next section.
The time bounds of an Open MCT application are defined as numbers, and a Time System gives meaning and context to these numbers so that they can be correctly interpreted. Time Systems are JavaScript objects that provide some information about the current time reference frame. An example of defining and registering a new time system is given below:
openmct.time.addTimeSystem({
key: 'utc',
name: 'UTC Time',
cssClass = 'icon-clock',
timeFormat = 'utc',
durationFormat = 'duration',
isUTCBased = true
});
The example above defines a new utc based time system. In fact, this time system
is configured and activated by default from index.html
in the default
installation of Open MCT if you download the source from GitHub. Some details of
each of the required properties is provided below.
key
: Astring
that uniquely identifies this time system.name
: Astring
providing a brief human readable label. If the Time Conductor plugin is enabled, this name will identify the time system in a dropdown menu.cssClass
: A class namestring
that will be applied to the time system when it appears in the UI. This will be used to represent the time system with an icon. There are a number of built-in icon classes available in Open MCT, or a custom class can be used here.timeFormat
: Astring
corresponding to the key of a registered telemetry time format. The format will be used for displaying discrete timestamps from telemetry streams when this time system is activated. If the UTCTimeSystem is enabled, then theutc
format can be used if this is a utc-based time systemdurationFormat
: Astring
corresponding to the key of a registered telemetry time format. The format will be used for displaying time ranges, for example00:15:00
might be used to represent a time period of fifteen minutes. These are used by the Time Conductor plugin to specify relative time offsets. If the UTCTimeSystem is enabled, then theduration
format can be used if this is a utc-based time systemisUTCBased
: Aboolean
that defines whether this time system represents numbers in UTC terrestrial time.
Once registered, a time system can be activated by calling timeSystem
with
the timeSystem key
or an instance of the time system. If you are not using a
clock, you must also specify valid bounds for the
timeSystem.
openmct.time.timeSystem('utc', bounds);
A time system can be immediately activated after registration:
openmct.time.addTimeSystem(utcTimeSystem);
openmct.time.timeSystem(utcTimeSystem, bounds);
Setting the active time system will trigger a 'timeSystem'
event. If you supplied bounds, a 'bounds'
event will be triggered afterwards with your newly supplied bounds.
The TimeAPI provides a getter/setter for querying and setting time bounds. Time
bounds are simply an object with a start
and an end end
attribute.
start
: Anumber
representing a moment in time in the active Time System. This will be used as the beginning of the time period displayed by time-responsive telemetry views.end
: Anumber
representing a moment in time in the active Time System. This will be used as the end of the time period displayed by time-responsive telemetry views.
If invoked with bounds, it will set the new time bounds system-wide. If invoked without any parameters, it will return the current application-wide time bounds.
const ONE_HOUR = 60 * 60 * 1000;
let now = Date.now();
openmct.time.bounds({start: now - ONE_HOUR, now);
To respond to bounds change events, listen for the 'bounds'
event.
The Time API can be set to follow a clock source which will cause the bounds to be updated automatically whenever the clock source "ticks". A clock is simply an object that supports registration of listeners and periodically invokes its listeners with a number. Open MCT supports registration of new clock sources that tick on almost anything. A tick occurs when the clock invokes callback functions registered by its listeners with a new time value.
An example of a clock source is the LocalClock which emits the current time in UTC every 100ms. Clocks can tick on anything. For example, a clock could be defined to provide the timestamp of any new data received via a telemetry subscription. This would have the effect of advancing the bounds of views automatically whenever data is received. A clock could also be defined to tick on some remote timing source.
The values provided by clocks are simple number
s, which are interpreted in the
context of the active Time System.
A clock is an object that defines certain required metadata and functions:
key
: Astring
uniquely identifying this clock. This can be used later to reference the clock in places such as the Time Conductor configurationcssClass
: Astring
identifying a CSS class to apply to this clock when it's displayed in the UI. This will be used to represent the time system with an icon. There are a number of built-in icon classes available in Open MCT, or a custom class can be used here.name
: Astring
providing a human-readable identifier for the clock source. This will be displayed in the clock selector menu in the Time Conductor UI component, if active.description
: An optionalstring
providing a longer description of the clock. The description will be visible in the clock selection menu in the Time Conductor plugin.on
: Afunction
supporting registration of a new callback that will be invoked when the clock next ticks. It will be invoked with two arguments:eventName
: Astring
specifying the event to listen on. For now, clocks support one event -tick
.callback
: Afunction
that will be invoked when this clock ticks. The function must be invoked with one parameter - anumber
representing a valid time in the current time system.
off
: Afunction
that allows deregistration of a tick listener. It accepts the same arguments ason
.currentValue
: Afunction
that returns anumber
representing a point in time in the active time system. It should be the last value provided by a tick, or some default value if no ticking has yet occurred.
A new clock can be registered using the addClock
function exposed by the Time
API:
var someClock = {
key: 'someClock',
cssClass: 'icon-clock',
name: 'Some clock',
description: "Presumably does something useful",
on: function (event, callback) {
// Some function that registers listeners, and updates them on a tick
},
off: function (event, callback) {
// Some function that unregisters listeners.
},
currentValue: function () {
// A function that returns the last ticked value for the clock
}
}
openmct.time.addClock(someClock);
An example clock implementation is provided in the form of the LocalClock
Once registered a clock can be activated by calling the clock
function on the
Time API passing in the key or instance of a registered clock. Only one clock
may be active at once, so activating a clock will deactivate any currently
active clock. clockOffsets
must be specified when changing a clock.
Setting the clock triggers a 'clock'
event, followed by a 'clockOffsets'
event, and then a 'bounds'
event as the offsets are applied to the clock's currentValue().
openmct.time.clock(someClock, clockOffsets);
Upon being activated, the time API will listen for tick events on the clock by calling clock.on
.
The currently active clock (if any) can be retrieved by calling the same function without any arguments.
As of July 2023, this method will be deprecated. Open MCT will always have a ticking clock.
The stopClock
method can be used to stop an active clock, and to clear it. It
will stop the clock from ticking, and set the active clock to undefined
.
openmct.time.stopClock();
When a clock is active, the time bounds of the application will be updated
automatically each time the clock "ticks". The bounds are calculated based on
the current value provided by the active clock (via its tick
event, or its
currentValue()
method).
Unlike bounds, which represent absolute time values, clock offsets represent relative time spans. Offsets are defined as an object with two properties:
start
: Anumber
that must be < 0 and which is used to calculate the start bounds on each clock tick. The start offset will be calculated relative to the value provided by a clock's tick callback, or itscurrentValue()
function.end
: Anumber
that must be >= 0 and which is used to calculate the end bounds on each clock tick.
The clockOffsets
function can be used to get or set clock offsets. For example,
to show the last fifteen minutes in a ms-based time system:
var FIFTEEN_MINUTES = 15 * 60 * 1000;
openmct.time.clockOffsets({
start: -FIFTEEN_MINUTES,
end: 0
})
Note: Setting the clock offsets will trigger an immediate bounds change, as
new bounds will be calculated based on the currentValue()
of the active clock.
Clock offsets are only relevant when a clock source is active.
The Time API is a standard event emitter; you can register callbacks for events using the on
method and remove callbacks for events with the off
method.
For example:
openmct.time.on('bounds', function callback (newBounds, tick) {
// Do something with new bounds
});
The events emitted by the Time API are:
bounds
: emitted whenever the bounds change. The callback will be invoked with two arguments:bounds
: A bounds bounds object representing a new time period bound by the specified start and send times.tick
: Aboolean
indicating whether or not this bounds change is due to a "tick" from a clock source. This information can be useful when determining a strategy for fetching telemetry data in response to a bounds change event. For example, if the bounds change was automatic, and is due to a tick then it's unlikely that you would need to perform a historical data query. It should be sufficient to just show any new telemetry received via subscription since the last tick, and optionally to discard any older data that now falls outside of the currently set bounds. Iftick
is false,then the bounds change was not due to an automatic tick, and a query for historical data may be necessary, depending on your data caching strategy, and how significantly the start bound has changed.
timeSystem
: emitted whenever the active time system changes. The callback will be invoked with a single argument:timeSystem
: The newly active time system.
clock
: emitted whenever the clock changes. The callback will be invoked with a single argument:clock
: The newly active clock, orundefined
if an active clock has been deactivated.
clockOffsets
: emitted whenever the active clock offsets change. The callback will be invoked with a single argument:clockOffsets
: The new clock offsets.
The Time Conductor provides a user interface for managing time bounds in Open MCT. It allows a user to select from configured time systems and clocks, and to set bounds and clock offsets.
If activated, the time conductor must be provided with configuration options, detailed below.
The time conductor is configured by specifying the options that will be
available to the user from the menus in the time conductor. These will determine
the clocks available from the conductor, the time systems available for each
clock, and some default bounds and clock offsets for each combination of clock
and time system. By default, the conductor always supports a fixed
mode where
no clock is active. To specify configuration for fixed mode, simply leave out a
clock
attribute in the configuration entry object.
Configuration is provided as an array
of menu options. Each entry of the
array is an object with some properties specifying configuration. The configuration
options specified are slightly different depending on whether or not it is for
an active clock mode.
Configuration for Fixed Time Mode (no active clock)
timeSystem
: Astring
, the key for the time system that this configuration relates to.bounds
: ATime Bounds
object. These bounds will be applied when the user selects the time system specified in the previoustimeSystem
property.zoomOutLimit
: An optionalnumber
specifying the longest period of time that can be represented by the conductor when zooming. If azoomOutLimit
is provided, then azoomInLimit
must also be provided. If provided, the zoom slider will automatically become available in the Time Conductor UI.zoomInLimit
: An optionalnumber
specifying the shortest period of time that can be represented by the conductor when zooming. If azoomInLimit
is provided, then azoomOutLimit
must also be provided. If provided, the zoom slider will automatically become available in the Time Conductor UI.
Configuration for Active Clock
clock
: Astring
, thekey
of the clock that this configuration applies to.timeSystem
: Astring
, the key for the time system that this configuration relates to. Separate configuration must be provided for each time system that you wish to be available to users when they select the specified clock.clockOffsets
: AclockOffsets
object that will be automatically applied when the combination of clock and time system specified in this configuration is selected from the UI.
An example time conductor configuration is provided below. It sets up some default options for the UTCTimeSystem and LocalTimeSystem, in both fixed mode, and for the LocalClock source. In this configutation, the local clock supports both the UTCTimeSystem and LocalTimeSystem. Configuration for fixed bounds mode is specified by omitting a clock key.
const ONE_YEAR = 365 * 24 * 60 * 60 * 1000;
const ONE_MINUTE = 60 * 1000;
openmct.install(openmct.plugins.Conductor({
menuOptions: [
// 'Fixed' bounds mode configuation for the UTCTimeSystem
{
timeSystem: 'utc',
bounds: {start: Date.now() - 30 * ONE_MINUTE, end: Date.now()},
zoomOutLimit: ONE_YEAR,
zoomInLimit: ONE_MINUTE
},
// Configuration for the LocalClock in the UTC time system
{
clock: 'local',
timeSystem: 'utc',
clockOffsets: {start: - 30 * ONE_MINUTE, end: 0},
zoomOutLimit: ONE_YEAR,
zoomInLimit: ONE_MINUTE
},
//Configuration for the LocaLClock in the Local time system
{
clock: 'local',
timeSystem: 'local',
clockOffsets: {start: - 15 * ONE_MINUTE, end: 0}
}
]
}));
Indicators are small widgets that reside at the bottom of the screen and are visible from every screen in Open MCT. They can be used to convey system state using an icon and text. Typically an indicator will display an icon (customizable with a CSS class) that will reveal additional information when the mouse cursor is hovered over it.
A common use case for indicators is to convey the state of some external system such as a persistence backend or HTTP server. So long as this system is accessible via HTTP request, Open MCT provides a general purpose indicator to show whether the server is available and returning a 2xx status code. The URL Status Indicator is made available as a default plugin. See the documentation for details on how to install and configure the URL Status Indicator.
A simple indicator with an icon and some text can be created and added with minimal code. An indicator of this type exposes functions for customizing the text, icon, and style of the indicator.
eg.
var myIndicator = openmct.indicators.simpleIndicator();
myIndicator.text("Hello World!");
openmct.indicators.add(myIndicator);
This will create a new indicator and add it to the bottom of the screen in Open MCT.
By default, the indicator will appear as an information icon. Hovering over the icon will
reveal the text set via the call to .text()
. The Indicator object returned by the API
call exposes a number of functions for customizing the content and appearance of the indicator:
.text([text])
: Gets or sets the text shown when the user hovers over the indicator. Accepts an optionalstring
argument that, if provided, will be used to set the text. Hovering over the indicator will expand it to its full size, revealing this text alongside the icon. Returns the currently set text as astring
..description([description])
: Gets or sets the indicator's description. Accepts an optionalstring
argument that, if provided, will be used to set the text. The description allows for more detail to be provided in a tooltip when the user hovers over the indicator. Returns the currently set text as astring
..iconClass([className])
: Gets or sets the CSS class used to define the icon. Accepts an optionalstring
parameter to be used to set the class applied to the indicator. Any of the built-in glyphs may be used here, or a custom CSS class can be provided. Returns the currently defined CSS class as astring
..statusClass([className])
: Gets or sets the CSS class used to determine status. Accepts an optionalstring
parameter to be used to set a status class applied to the indicator. May be used to apply different colors to indicate status.
A completely custom indicator can be added by simply providing a DOM element to place alongside other indicators.
var domNode = document.createElement('div');
domNode.innerText = new Date().toString();
setInterval(function () {
domNode.innerText = new Date().toString();
}, 1000);
openmct.indicators.add({
element: domNode
});
Open MCT provides some built-in priority values that can be used in the application for view providers, indicators, root object order, and more.
Currently, the Open MCT Priority API provides (type: numeric value):
- HIGH: 1000
- Default: 0
- LOW: -1000
View provider Example:
class ViewProvider {
...
priority() {
return openmct.priority.HIGH;
}
}