Elevation model: Difference between revisions
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==Elevation model generation== | ==Elevation model generation== | ||
[[File:Ahn.jpg|300px|thumb|right|The [[Advanced options (New project Wizard)|advanced options]] allow you to select data sources and | The elevation model is generated when a [[Project]] is first created. The [[Advanced options (New project Wizard)|advanced options]] allow you to select the used data sources and resolution for the elevation model. | ||
[[File:Ahn.jpg|300px|thumb|right|The [[Advanced options (New project Wizard)|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: | In the Netherlands, the following data sources are used to construct the elevation model: | ||
{|class=wikitable | {|class=wikitable | ||
! Name | ! Name | ||
! | ! Resolution | ||
! Description | ! Description | ||
! Source | ! Source | ||
|- | |- | ||
| ESRI DTM | | ESRI DTM | ||
| 3m by 3m | | 3m by 3m | ||
| Dataset supplied by Rijkswaterstaat to ESRI, based on AHN2. | | Dataset supplied by Rijkswaterstaat to ESRI, based on AHN2. | ||
| Line 32: | Line 31: | ||
|- | |- | ||
| AHN DSM | | AHN DSM | ||
| 0.5m by 0.5m, 1m by 1m, or 2.5m by 2.5m, depending on [[Advanced options (New project Wizard)|selected options]]. | | 0.5m by 0.5m, 1m by 1m, or 2.5m by 2.5m, depending on [[Advanced options (New project Wizard)|selected options]]. | ||
| Raw data from [http://www.ahn.nl Actuele Hoogte Bestand] | | Raw data from [http://www.ahn.nl Actuele Hoogte Bestand] | ||
| Line 38: | Line 36: | ||
|- | |- | ||
| AHN DTM | | AHN DTM | ||
| 0.5m by 0.5m, 1m by 1m, or 2.5m by 2.5m, depending on [[Advanced options (New project Wizard)|selected options]]. | | 0.5m by 0.5m, 1m by 1m, or 2.5m by 2.5m, depending on [[Advanced options (New project Wizard)|selected options]]. | ||
| Interpolated (surface level) data based on [http://www.ahn.nl Actuele Hoogte Bestand] | | Interpolated (surface level) data based on [http://www.ahn.nl Actuele Hoogte Bestand] | ||
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|- | |- | ||
| Features | | Features | ||
| | | | ||
| Presence of features of the built environment | | Presence of features of the built environment | ||
| Line 50: | Line 46: | ||
|} | |} | ||
By default the AHN3 is used for the DTM | By default the AHN3 is used for the DTM and DSM. If the AHN3 is [[Advanced options (New project Wizard)|deactivated]] in the [[Advanced options (New project Wizard)|Advanced options panel]], AHN2 is used. | ||
===DTM | ===DTM=== | ||
The DTM is | The DTM is generated as follows: | ||
* The ESRI DTM is resampled to the same resolution as the AHN DTM and AHN DSM. | * 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. | * 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. | * In locations where the AHN DTM has NO_DATA values (such as waterbodies), the ESRI DTM is used. | ||
* Optionally, if [[Advanced options (New project Wizard)| | * Optionally, if [[Advanced options (New project Wizard)|optional thresholds are applied]], 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 | ** Bare land | ||
** Roads | ** Roads | ||
** Crop fields/agriculture | ** Crop fields/agriculture | ||
===DSM | ===DSM=== | ||
For [[Construction]]s, the average height of the AHN DSM is determined for the | For [[Construction]]s, the average height of the AHN DSM is determined for the polygon defining the buildings 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 [[Construction]]s | Using image recognition techniques, the footprint polygon of the [[Construction]]s is split into multiple [[Construction section]]s, 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 resulting [[Construction]] heights are not made part of the DSM. Instead, they are stored as properties of the [[Construction]]s in the [[Project]]. | ||
===Water=== | ===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 [[water depth m (Terrain Attribute)|default water depth]] of the determined [[Terrain Type]] of the | * The [[water depth m (Terrain Attribute)|default water depth]] of the determined [[Terrain Type]] of the waterbody is used. | ||
* The [[angle of repose (Terrain Attribute)|angle of repose]] of the underground [[Terrain Type]] present at or near the sides of the | * The [[angle of repose (Terrain Attribute)|angle of repose]] of the underground [[Terrain Type]] present at or near the sides of the waterbodies. | ||
<br> | |||
From the DTM a heightpoint in or as close to the wateredge is taken. On that point the [[Terrain#Subsurface|Underground Terrain Type]] is determined and its angle of respose value. 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. | |||
==Elevation model generation (outside the Netherlands)== | ==Elevation model generation (outside the Netherlands)== | ||
Revision as of 10:33, 21 August 2020
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What is an 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 3-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. Therefore 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.
Heightmap Overlay
- Main article: Heightmap Overlay
More insight into the elevation model can be provided by adding the Heightmap Overlay, which is a Grid Overlay showing the (average) height of the terrain per grid cell. You can add the DSM and DTM Heightmap Overlays.
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.
DTM
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 optional thresholds are applied, 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
For Constructions, the average height of the AHN DSM is determined for the polygon defining the buildings 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 is 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 DSM. 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 heightpoint in or as close to the wateredge is taken. On that point the Underground Terrain Type is determined and its angle of respose value. 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.
Elevation model generation (outside the Netherlands)
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