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About BiRDview

BiRDview is an open source web-application for visualization of Bidirectional Reflectance Distribution Function (BRDF) measurement data. It was developed as one of the results of Joint Research Project Bidirectional Reflectance Definitions (BiRD, JRP 16NRM08) supported by EMPIR initiative of EURAMET.

Application is written in Python using Plotly Dash open source library and the code can be found here.

Current version of application allows to open and view files only in the file format developed and agreed by BiRD consortium.

Universal BRDF data format

BRDF file format is based on json syntax. I.e. it is a text file that stores data in dictionaries in the form of:

{key: value}

where key is 'string' type and value can be 'string', 'number', 'array', 'True', 'False', 'Null' or 'object' i.e. another '{key: value}' structure.

Consortium agreed on following keys and structure in the BRDF file format that are thoroughly described in following documentation web-page.

File can have extension .json or .brdf.

File can be validated using following JSON Schema: brdf_json_schema_v1.0.json.

Example (toggle code/tree options to study the file):

Quick guide

Uploading file

To upload the BRDF file in the "Applet" tab locate upload field where you can either drag and drop files or open a file selection dialogue to choose files to be opened. Uploading of multiple files is allowed and "loading" animation will be shown until all files are loaded. Uploaded file's/files' name will appear in the dropdown menu below upload field. Uploading of files with the same name is also allowed. In this case a suffix "_copy_N" will be added to file name where N corresponds to number of copies.

Selecting uploaded file

To select one of the uploaded files as an active, click dropdown menu with file names and select file by clicking on its file name. After that menu with file parameters as well as figures will be updated to correspond to selected file.

Navigating through data parameters and figures

By definition BRDF data has more than 3 dimensions that makes it impossible to depict all the data on a single figure. For this reason smaller pieces of data should be selected and depicted on multiple figures. In BiRD view this can be performed by using dropdown menus located under file selection dropdown. There, corresponding to BRDF file format, you can select: incidence zenith angle, incidence azimuthal angle, viewing zenith angle, viewing azimuthal angle and any additional available parameters (from top to bottom). All parameters remain unique to every file. That means when you change parameters for one file, they are not changed for other files and applet remembers choices for each file.

Choices can be made by clicking corresponding dropdown and selecting desired parameter value.

Metadata of the file can be acessed through a "Metadata" tab within file menu:

Changing data parameters will update the figures located on the right from file menu dropdowns'. There are currently two tabs that allow you to explore BRDF data in terms of raw values and CIELAB values calculated from them.

There are four figures for BRDF data viewing. First - top left - provides the 3D shape of BRDF at specified incidence zenith and azimuthal angles as well as all other parameters. Changing these parameters will cause figure to update. Dots on the figure represent measured data points and by hovering the mouse over them one can see measured values. Color coded surface drawn though measured points gives an idea about the shape of the BRDF.

Bottom left figure represents the projection of 3D plot to the XY plane and converted to the polar plot. By rotating plot one can select viewing azimuthal angle in parallel with corresponding dropdown menu. This selects a plane for 2D BRDF plot located on the right (bottom-right).

2D BRDF plot shows you the BRDF at specified incidence zenith, azimuthal angles, additional parameters and selected viewing azimuthal angle. Changing these parameters will cause graph to update. By clicking on a point located shown on this graph you can see the reflectance spectrum at this point.

Last graph located at the upper right corner can show 2D BRDF dependence on any parameter selected as X including additional parameters. To select parameter as X use dropdown menu named "Select variable as X". Upon selection graph will be updated and desired BRDF dependence on selected parameter will be shown.

Viewing data from multiple files at the same time

On 2D plots user can plot and compare data from one and the same file or from different files. To do that one needs to take a snapshot of file menu state by pressing "Snap state" button. When state is snapped BiRDview will remember it and plot it alongside any other state from file menu or other sanaped states.

Basics on figures' controls

As was mentioned before, BiRDview app uses plotly graphing library that allows to create quite interactive figures. You can move graphs, rotate them, zoom to specific areas, get information by hovering mouse over data points and much more. Don't be afraid to learn by trial and remember that you can return to initial states either by double-clicking on the plot or by using home button on the figure menu that appears in the upper right corner of the graphs when you hover your mouse over them. In menu you can also find other useful option and save figures as .png files.


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