Elevation model
An elevation model (or DEM, Digital Elevation Model), is a model representation of terrain heights; the quantitative measurement of vertical elevation change in a landscape. On a small scale, differences in terrain height can affect shade and water distribution. On a larger scale, terrain height has an effect on weather and climate patterns.
Implementation in the Tygron Platform
The elevation model (also referred to as DEM) in the Tygron Platform is a 2-dimensional grid with values indicating the terrain height in meters relative to datum. Terrain in this context meaning the soil and the subsurface.
The 3D World visualizes the elevation model inherently as the bottom plane upon which all other features, such as Constructions, are placed. Changes in terrain height are similarly changes in the height of that plane.
In the Tygron Platform, the elevation model offers terrein heights representation as both a DTM (Digital Terrain Model) and as a DSM (Digital Surface Model). A DTM represents the bare ground surface without any objects like plants and buildings. In contrast; a DSM represents the earth's surface including all objects (e.g. houses, trees, etc.) on it. This means features such as Constructions are explicitly not a part of the DTM, but are a part of the DSM. In locations with water, the elevation model follows the bottom of the water body for both the DTM and the DSM.
The 3D World visualizes the elevation model inherently as the bottom plane upon which all other features, such as Constructions, are placed. Changes in terrain height are similarly changes in the height of that plane.
The elevation model consists of a single dataset, which is generated when a Project is first created. Any changes to the elevation model are applied directly to that dataset, including manually drawn changes as well as imported changes.
Heightmap Overlays
More insight into the elevation model can be provided by adding the Digital Terrain Model Overlay or the Digital Surface Model Overlay , which are Grid Overlay showing the (average) height per grid cell.
Elevation model generation
The elevation model is generated when a Project is first created. The advanced options allow you to select the used data sources and resolution for the elevation model.
In the Netherlands, the following data sources are used to construct the elevation model:
- By default the AHN3 is used for the DTM and DSM. If the AHN3 is deactivated in the advanced options panel, AHN2 is used.
- By default the BGT is used for the features in the 3D World. If the BGT is deactivated in the advanced options panel, TOP10NL is used.
DTM (Terrain height)
The DTM is generated as follows:
- The ESRI DTM is resampled to the same resolution as the AHN DTM and AHN DSM.
- The AHN DTM serves as the base data for the resulting elevation model DTM.
- In locations where the AHN DTM has NO_DATA values (such as waterbodies), the ESRI DTM is used.
- Optionally, if the option for applying thresholds is selected, the AHN DSM heights are used instead of the so far determined DTM heights, if the difference between the two does not exceed a certain threshold. The following features can have the DSM heights applied instead:
- Bare land
- Roads
- Crop fields/agriculture
DSM (construction height)
For Constructions, the average height of the AHN DSM is determined for the polygon defining the Construction's footprint.That average height of the AHN DSM is then determined to be the height of the Construction.
Using image recognition techniques, the footprint polygon of the Constructions may be split into multiple Construction sections, each with their own polygon. The AHN DSM's average height is then determined per individual section, so that the variability in the rooftops of the Construction can be taken into account.
The resulting Construction heights are not made part of the DTM. Instead, they are stored as properties of the Constructions in the Project.
Water
Water bodies, found in terrain surface types, are lowered a few meters relative to the elevation of the surrounding surface. The following parameters are used:
- The default water depth of the determined Terrain Type of the waterbody is used.
- The angle of repose of the Underground Terrain Type present at or near the sides of the waterbodies.
From the DTM a point is selected at the waterbody's edge, or as close as possible. The Angle of repose value of the underground Terrain Type present in that point is determined. A downward slope is created at the determined angle of repose. The downward slope continues until either it meets the slope generated from the other end, or it reaches the determined default water depth relative to the DTM. This means that thin waterways will not be as deep as their default water depth allows them to be, and that large water bodies are likely to have flat water bottoms.
The resulting terrain height changes are made part of the DTM.
Elevation model generation (outside the Netherlands)
For the elevation model in projects abroad, the ESRI DTM is used. The resolution differs per location, based on the used data sources for creating the ESRI DTM layer.
| Name | Resolution | Description | Source |
|---|---|---|---|
| ESRI DTM | Differs per location, see the metadata for more information | Ground height dataset of ESRI, based on multiple sources. | https://www.arcgis.com/home/item.html?id=58a541efc59545e6b7137f961d7de883 |
For the DSM height, the heights of Constructions are used. If available, the OSM building heights are used, otherwise the default heights. The default heights differ per function, based on the default floors and floor height.
How-to's
- How to change how the default elevation model is generated
- How to import a GeoJSON to change the elevation model
- How to import a GeoTIFF to change the elevation model
- How to import a GeoJSON of waterways
- How to import a GeoTIFF of waterway depths
- How to use the terrain height brush in selection mode
- How to use the terrain height brush in live sculpting mode
- How to export the elevation model