Grid Overlay
What is a grid overlay
A grid overlay is a calculated overlay. The calculation divides the entire 3D world up into a grid of cells, with cells ranging from 0.25m² to 100m². This amounts to anywhere from thousands to millions of cells per overlay. For each cell, a calculation is performed, the specifics of which depend on the overlay being calculated.
How are grid calculations performed
Depending on the exact overlay being calculated, the specifics of the calculation may differ, but the general approach is identical for each overlay.
Each calculation relies on some data, which may be set as properties or attributes of the overlay, or may be based on the features present in an individual cell. This data is read from their respective locations as input for the calculation. Data from surrounding cells may also be included, in which their distance may also be factored in.
With all the data obtained, a new values or set of values is calculated for the cell, and stored as result data for that cell. The calculation may specify this processing repeating a large number of times, for example when iterating through time steps.
When the calculation is completed, a final result value is stored in the cell. The value stored in the cell itself is a unitless number. The exact meaning of the number is dependent on the overlay which defines the calculation. A calculation for noise will present its result in decibels. A calculation for subsidence in meters.
Grid recalculation
During a session, grids are automatically recalculated whenever a change is made to the state of the 3D world, including non-geographical data such as globals or attributes. While editing, a grid is also updated when 3D world data is changed. However, some parameters can be changed in the editor which cannot be changed during a session, such as the properties or attributes of overlays. To prevent more complex overlays slowing down editing work, a grid overlay is not always automatically recalculated when these kinds of parameters are changed. To force the grids to recalculate, the "Refresh grid" option can be used on any grid overlay. This will force all grids to recalculate.
Using grid results
The results of a grid overlay calculation can be used in multiple ways.
Overlay
The results of the overlay are displayed in the 3D world. By selecting the overlay in the session interface, the world will be colored based on the calculated values. This allows the end-user to inspect the results visually and geographically.
The legend displayed while the overlay is active can be configured to fit the magnitude and intent of the colors of the overlay.
TQL
The results of the calculation can be queries using TQL. Queries can either retrieve data of the grid directly, such as the average value in a given location, or use it as a filter for other queries, by specifying a value the grid should have before taking that location into account.
Export
The results can be exported as a geotiff file. This is a georeferenced image consisting of a grid of cells. Each cell has a value, which is displayed as a color on the spectrum of black to white. It's also possible to load a geotiff into a GIS application, allowing you to further process the results of the calculations performed in the Tygron Platform.
- Select any grid overlay in the editor.
- On the right panel, select "Export as GeoTiff".
Settings
The grid overlays share a few settings, which influence the accuracy of the calculations. Depending on the calculation performed and the use-case forming the project's context, it may be desirable to tweak the settings used for the grid overlays. For performance reasons it is not possible to set grid overlay settings to different values for different overlays in the same project.
Grid size
The more cells that need to be calculated, the more resources (and in the end: time) it will take to complete the calculation. Depending on the use-case and the calculation being performed, it may be desirable to change the grid size used for the grid overlays. The world is divvied up into cells of the specified size.
Note: if you select a grid size which does not neatly divide your project size, the south- and eastern edges of the project may not be covered by the grid, and not taken into account during a calculation.
Grid Accuracy Threshold
As the grid size decreases (and thus more cells exist in the project), calculations will take longer to complete. Under normal circumstances, when a calculation is based on geographical parameters, all contents of the cell are checked and all objects relevant to the calculation are taken into consideration based on how much of the cell is covered by it. When the grid size falls below this threshold, the method for determining these parameters changes. Instead, the exact center of the cell is checked, and if relevant data is found it is taken into consideration as if it were present in the entire cell. This is less accurate, but allows the calculation to complete faster.
Configuring Grid Settings
Template:Editor ribbon When any grid overlay has been added to a project, it is possible to change the settings for the grid calculations. The grid settings are shared across all overlays, so adjusting the settings via one grid overlay will affect all grid overlays in the project.
- Select any grid overlay in the editor.
- On the right panel, select "Change Grid".
- Change the cell size to the desired size.
- Change accuracy threshold to the desired threshold.
- Select "Send".
- Select any grid overlay in the editor.
- On the right panel, select "Change Grid".
- Select "Reset to Default".
- Select "Send".