Exploring iModel Data QA (Jump Start)

[roopksaini]

RECORDINGS

Captured Q&A from the iModel.js Jump Start event on July 15th 2020, “Exploring iModel Data”.

In this session, Roop Saini spoke about how to read data from an iModel. He introduced two essential tools for data discovery 1) iModel Console that allows developers to construct ECSQL queries, and 2) iModel Schema Explorer for exploring and understanding how data is structured within an iModel.

Please don't reply to this discussion. If you have follow-up questions or comments please start a new discussion.

[roopksaini]

Q: What is the difference between iModel.js and Autodesk Forge? 
A: In quick summary, Forge is not open, does not scale as well, and does not have a concept of change. Of course, this is a big topic. Please contact us for more information.

Q: How do you access the iModel schema editor?
A: The easiest way to get to the schema editor is:

1. Start at imodelconsole.bentley.com

2. Open an iModel by selecting a project, iModel, changeset.

3. Click on the 'gear' icon in the upper right corner and choose 'Schema Explorer'

That will show you all the schemas from the iModel you opened.
You can also go directly to imodelschemaeditor.bentley.com which will show a generic set of schemas.

Q: Is it possible to add physical elements to an existing reality mesh? For example, if a given DOT has a 3D drone generated model of a bridge, is there currently a way to add/draw elements on the model and make an iModel?
A: We generally don't import reality meshes into an iModel due to their large size. You could create a physical model based on the realty data and show them together with iModel.js. I do not think we have any facility specifically for this today in iModel.js but if you are interested in this topic, I suggest talking to the core team outside of this session.

Q: Why is it so important to establish the relationship between instances?
A: In this session, Roop demonstrates how to implement the 'cross probing' feature. When a user clicks on a 2d element, the program needs to highlight the corresponding 3d element. To do that, we need to know which element should be highlighted.

Q: Do I need to have Bentley account to access to iModels?
A: You can access some of our samples and use snapshot iModels without an account but to access the iModelHub you need a Bentley account. You can go to the link to get started, and create a free account when asked to log in (https://www.imodeljs.org/getting-started/).

Q: What is a model? Is it the system that we are designing or a model file as per desktop context?
A: A model is a container for elements within an iModel. The concept is similar to the model concept in dgn files.

Q: Does this imply that the 2D drawings have been generated from the 3D models?
A: Not necessarily, the two could have been created in OpenPlant PID and OpenPlant Modeler, but a link was created between the two either in the source applications or during bridging. It is also possible to create links between elements using iModel.js.

Q: The BIS schemas seems like a relational database, is it possible to connect the iModel with a general-purpose database browser, like DBeaver?
A: iModels map BIS into the lower level database schemas. This helps support a higher-level query language (we call it "ECSQL" - it adheres to standard SQL wherever possible) that gets translated into low-level SQL queries for execution. This way queries based on classes, properties, and relationships are converted to SQL and executed on the underlying SQLite database. So, to answer your question, the underlying format for the iModel is SQLite, so you can use tools like DBeaver for accessing it. However, for all practical purposes, we believe ECSQL provides a higher level, richer and more useful API.

Q: Why does the Desktop Starter display weird fonts (decorated with punctuation)? Is it an Electron setting?
A: It’s called pseudo-localization and its purpose is to help debug localization issues. It allows you locally to find which strings have not been setup for localization. This will not show up in a production build.

Q: When you have an iModel with a master file and references, how can you return the model tree with an ECSQL query? For example, from the master file find all references.
A: You can query the subjects in an iModel to see the master and reference files. Here is a basic query to get you started:

SELECT p.userlabel parentLabel, p.codevalue parent_Code, s.userlabel label, s.codevalue code
FROM bis.subject s
LEFT JOIN bis.subject p
ON p.ecinstanceid = s.parent.id

You can also use our presentation rules system to get back a tree hierarchy that is easy to display in the tree we provide with iModel.js or in your own tree.

Q: Where exactly are the relationships and the data of the model stored in your example?
A: The relationships are stored using link tables or foreign keys inside of the iModel.

Q: Are these schemas created from the drawings when you generate the iModel as explained yesterday?
A: During synchronization, each bridge adds the schemas necessary to represent the data from the source files.

Q: Will there be any discussion about raster overlays (from remote sensing)?
A: iModel.js allows aggregating data from multiple data sources, and for instance, we use it to overlay reality data. This however is an advanced topic beyond the scope of this JumpStart session. Please feel free to reach out for a more involved discussion on your use case.

Q: Are we speaking about the Digital Twin as the 3D model or a combination of different type of models such as Advanced Simulators and AI and as an optional part of the 3D model? What do you think about this DT approach?
A: We think of the Digital Twin as being larger than an iModel. An iModel can be an important part of a digital twin, but not all twins will even have an iModel. The iModel.js libraries can federate data from many sources into a combined experience.

Q: When I change the corridor solution in OpenRoads, does the element ID in the iModel change?
A: No, the Element ID that is unique in the iModel will be consistent for the lifetime of the instance of the Element. The only time it will change is if the instance is removed in OpenRoads and then added back. There are some edge cases such as if the ECClass changes but for the general case it does stay consistent.

Q: In the list of supported Bentley Design Applications I don’t see any Oil & Gas specific brands like SACS or MOSES. Are there any plans to expand this list of applications?
A: Creating new bridges and improving existing bridges is always ongoing. Please contact us to tell us about your specific requirements.

Q: In a scenario with a 3D model (PDMS) and 2D model (DWG), is the bridge the tool used to map the entities and bring them into iModel.js?
A: Yes. Bridges synchronize data from the source file into the iModel incrementally as data changes in the source file.

Q: How are you working with IoT hub from Microsoft?
A: Check out this channel9 video: https://channel9.msdn.com/Shows/Internet-of-Things-Show/Bentley-iTwin-and-iModeljs-Integration-with-Azure-Digital-Twins?term=bentley&lang-en=true

We have another one specifically on IOT coming up in a few weeks: https://channel9.msdn.com/Shows/Internet-of-Things-Show/Deep-Dive-Integrating-3D-Models-and-IoT-data-with-iTwin-and-Azure-Digital-Twins?term=bentley&lang-en=true

Here is a blog post on the subject as well: https://medium.com/imodeljs/road-to-iot-15a6ce1c43e1

Q: Is the data in an iModel divided into separate files? If I would need to transfer an iModel project to another company in order to visualize it, what should I transfer?
A: For sharing data with another company, there is no need to transfer any data. You can simply grant them access to the iModel. That said, the data of an iModel is stored within a single file. Keep in mind that an iModel is only one component of a digital twin which may also include reality meshes, IOT streams, etc.