Terrain height: Difference between revisions

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==Terrain height in the {{software}}==
==Terrain height in the {{software}}==


===DTM for projects in The Netherlands===
#REDIRECT [[Terrain height]]
{{learned|what an elevation model is|what is considered part of the {{software}}'s elevation model|how the {{software}} generates an elevation model|how to enrich or replace the elevation model with your own data}}
{{stub}}
{{being updated}}
==What is an elevation model==
[[File:DTM_DSM.png|thumb|200px|left|Source: https://commons.wikimedia.org/wiki/File:DTM_DSM.svg]]
An elevation model, also known as a Digital Surface Model (DSM) or Digital Terrain Model (DTM) as appropriate, 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.{{clear}}


====Data sources====
==How is the elevation model implemented in the {{software}}==
In the Netherlands a DTM is constructed using the following data sources:
In the {{software}}, the elevation model offers terrein heights representation as both a DTM and as a DSM. Specifically, it is a 2-dimensional grid with values indicating the terrain height in meters relative to {{datum}}. Terrain in this context meaning the soil and everything below it. Features such as [[Construction]]s are explicitly not a part of the DTM, but are a part of the DSM. In locations with [[Water (Terrain Attribute)|water]], the elevation model follows the bottom of the water body for both the DTM and the DSM.
* A base DTM, with a cell size of 3mx3m, supplied by Rijkswaterstaat to [http://www.arcgis.com/home/item.html?id=58a541efc59545e6b7137f961d7de883 ESRI], based on the AHN2.
* A DSM from [http://www.arcgis.com/home/item.html?id=55df27e20c0d42e3a8bd48bc74c5c8cc AHN2] or [http://www.arcgis.com/home/item.html?id=b87c68ea246c4b17807cdad486279a47 AHN3] raw data ([http://www.ahn.nl Actuele Hoogte Bestand]) with a cell-size of 0.5x0.5m, 1x1m or 2.5x2.5m.
* A DTM from [http://www.arcgis.com/home/item.html?id=9d62ff8889ba41b2b712a68c7493bd16 AHN2] or [http://www.arcgis.com/home/item.html?id=9d62ff8889ba41b2b712a68c7493bd16 AHN3] containing interpolated ("maaiveld") data from ESRI, with a cell-size of 0.5x0.5m, 1x1m or 2.5x2.5m.
* [https://www.pdok.nl/introductie/-/article/basisregistratie-grootschalige-topografie-bgt- BGT] or [https://www.pdok.nl/introductie/-/article/basisregistratie-topografie-brt-historie Top10NL] data.


====Options====
The [[3D World]] visualizes the elevation model inherently as the bottom plane upon which all other features, such as [[Construction]]s, are placed. Changes in terrain height are similarly changes in the height of that plane.
When defining a new project, you can adjust the following [[Advanced options|'''Advanced Options''']] at the [[wizard]] to control the DTM and DSM data used.
These options are:
* ''Use AHN3 DSM instead of AHN2'': by default the AHN3 will be used for both the DTM and DSM. When not selected, the AHN2 data is used for the DTM and DSM.
* ''DEM Resolution'': The AHN is available on 0.5m, 1m or 2.5m resolution in the project database for generating the elevation grid (see the image below). Select the resolution appropriate for your project's needs.
* ''Apply DSM to DTM Thresholds for Land, Roads, and Other'': Optionally, the AHN DSM data can be applied to the DTM for height differences below the provided thresholds, based on the topography. This option can be useful when the DTM is too much averaged and smoothed and more variation is desirable. By default however, this option is turned off. When selected, the thresholds and resulting behavior will be:
** for bare lands the default threshold is 100cm: for all cells with a difference <100cm between the DTM and DSM, the value will be taken from the DSM
** for roads the default threshold is 25cm: for all cells with a difference <25cm between the DTM and DSM, the value will be taken from the DSM
** for crop-lands, scrup-land, etc the default threshold is 50cm: for all cells with a difference <50cm between the DTM and DSM, the value will be taken from the DSM
It is possible to change the default thresholds. To do so, change the corresponding value in the [[Advanced options|'''Advanced Options''']] menu (see the image below). The first value is for bare lands, the second for the roads and the third for the crop-lands etc. <br>


===Heightmap Overlay===
{{main|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 size|grid cell]].


[[File:Ahn.jpg|600px]]


====DTM generation====
==Elevation model generation==
A project's DTM is created with the following steps:
[[File:Ahn.jpg|300px|thumb|right|The [[Advanced options (New project Wizard)|advanced options]] allow you to select data sources and resolutions for the elevation mode.]]
* The ESRI DTM is resampled to the same resolution of the AHN DTM and AHN DSM.
In the Netherlands, the following data sources are used to construct the elevation model:
* The AHN DTM is set as the base DTM.
* The ESRI DTM is used to replace the NO_DATA values in the DTM, which can be present at waterbodies.
* Optionally, depending on the selected DSM to DTM advanced option, the DSM is applied to the DTM based on the topology value and the configured thresholds:
** for bare lands, all cells with a difference between the DTM and DSM < the first threshold, the value will be taken from the DSM
** for roads, all cells with a difference between the DTM and DSM < the second threshold, the value will be taken from the DSM
** for crop-lands, scrup-land etc, all cells with a difference between the DTM and DSM < the third threshold, the value will be taken from the DSM
[[File:Advanced_settings.JPG|600px]]


====DSM usage====
{|class=wikitable
Rooftops of buildings receive an average height of the DSM of the polygon defining the buildings footprint. The footprint is split into sections using image recognition techniques; herewith the variability in rooftops can be taken into account in the elevation model
! Name
! Type
! Detail
! Description
! Source
|-
| ESRI DTM
| DTM
| 3m&nbsp;by&nbsp;3m
| Dataset supplied by Rijkswaterstaat to ESRI, based on AHN2.
| http://www.arcgis.com/home/item.html?id=58a541efc59545e6b7137f961d7de883
|-
| AHN DSM
| DSM
| 0.5m&nbsp;by&nbsp;0.5m, 1m&nbsp;by&nbsp;1m, or 2.5m&nbsp;by&nbsp;2.5m, depending on [[Advanced options (New project Wizard)|selected options]].
| Raw data from [http://www.ahn.nl Actuele Hoogte Bestand]
| http://www.arcgis.com/home/item.html?id=55df27e20c0d42e3a8bd48bc74c5c8cc (AHN2) or http://www.arcgis.com/home/item.html?id=b87c68ea246c4b17807cdad486279a47 (AHN3)
|-
| AHN DTM
| DTM
| 0.5m&nbsp;by&nbsp;0.5m, 1m&nbsp;by&nbsp;1m, or 2.5m&nbsp;by&nbsp;2.5m, depending on [[Advanced options (New project Wizard)|selected options]].
| Interpolated (surface level) data based on [http://www.ahn.nl Actuele Hoogte Bestand]
| http://www.arcgis.com/home/item.html?id=9d62ff8889ba41b2b712a68c7493bd16 (AHN2) or http://www.arcgis.com/home/item.html?id=9d62ff8889ba41b2b712a68c7493bd16 (AHN3)
|-
| Features
|
|
| Presence of features of the built environment
| https://www.pdok.nl/introductie/-/article/basisregistratie-grootschalige-topografie-bgt- (BGT) or https://www.pdok.nl/introductie/-/article/basisregistratie-topografie-brt-historie (Top10NL)
|}


====Waterdepth====
===DTM (Terrain height)===
Water bodies, found in [[terrain]] surface types, are lowered a few meters relative to the elevation of the surrounding surface.  
* The ESRI DTM is resampled to the same resolution as the AHN DTM and AHN DSM.
By default:
* The AHN DTM serves as the base data for the resulting elevation model DTM.
*Boezemwater: 3m lowered relative to the elevation of the surrounding surface
* In locations where the AHN DTM has NO_DATA values (such as waterbodies), the ESRI DTM is used.
*Water: 2m lowered relative to the elevation of the surrounding surface
* Optionally, if [[Advanced options (New project Wizard)|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:
These values can be changed by changing the WATER_DEPTH_M attribute of the Terrain type.  
** Bare land
From the DEM a heightpoint in or as close to the wateredge is taken. On that point the Underground terrain type is determined. The slope (talud) of the sides of the water body is defined by the ANGLE_OF_REPOSE of this [[Terrain#Subsurface|Underground Terrain Types]] and the maximum depth to which a water body is carved out is WATER_DEPTH_M as defined for the surface terrain type on this point. If the angle of repose is shallow enough and the water body thin enough, the angled sides may meet up before the maximum water depth is reached. In this case the water body will be appropriately shallower.
** Roads
The ANGLE_OF_REPOSE attribute can also be changed.
** Crop fields/agriculture
 
===DSM (Construction height)===
For [[Construction]]s, the average height of the AHN DSM is determined for the [[Construction]]'s footprint polygon. 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 may be split up 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 DTM. Instead, they are stored as properties of the [[Construction]]s in the [[Project]].
===Water===
In locations with water features, the water's depth is "carved" into the DTM as determined up to this point. The following parameters are used to do so:
* The [[water depth m (Terrain Attribute)|default water depth]] of the determined [[Terrain Type]] of the water feature is used.
* The [[angle of repose (Terrain Attribute)|angle of repose]] of the underground [[Terrain Type]] present at or near the sides of the water feature.
Starting from the edges of the polygon of the water feature, 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 depth relative to the DTM. This means that thin waterrways 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)==
{{stub|type=section}}
 
==How-to's==
* [[How to change how the default elevation model is generated]]
* [[How to import a GeoTIFF as elevation model]]
* [[How to import a GeoJSON to change the elevation model]]
* [[How to import waterways]]
* [[How to export the elevation model]]
* [[How to use the terrain height brush in selection mode]]
* [[How to use the terrain height brush in live sculpting mode]]
 
==See also==
* [[Terrain]]
* [[Elevation model (Water Overlay)]]


==Changing terrain height==
==Changing terrain height==

Revision as of 10:21, 18 June 2020

Template:Learned

Terrain height

Terrain height is the whole of differences of terrain elevation in a given area, the quantitative measurement of vertical elevation change in a landscape. Terrain is used here as a general term in physical geography, referring to the lay of the land. This is usually expressed in terms of the elevation, slope, and orientation of terrain features. Terrain height - as element of a terrain - affects surface water flow and distribution. Over a large area, it can affect weather and climate patterns.
In overlays, the user can select two types of elevation, the digital terrain model (DTM) and digital surface model (DSM). 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.
DTM DSM.png
View original file here:[1]

Terrain height in the Tygron Platform

  1. REDIRECT Terrain height

Template:Learned

This article is a stub.
Please note: This page is currently being updated.

What is an elevation model

Source: https://commons.wikimedia.org/wiki/File:DTM_DSM.svg

An elevation model, also known as a Digital Surface Model (DSM) or Digital Terrain Model (DTM) as appropriate, 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.

How is the elevation model implemented in the Tygron Platform

In the Tygron Platform, the elevation model offers terrein heights representation as both a DTM and as a DSM. Specifically, it is a 2-dimensional grid with values indicating the terrain height in meters relative to datum. Terrain in this context meaning the soil and everything below it. 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.

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.


Elevation model generation

The advanced options allow you to select data sources and resolutions for the elevation mode.

In the Netherlands, the following data sources are used to construct the elevation model:

Name Type Detail Description Source
ESRI DTM DTM 3m by 3m Dataset supplied by Rijkswaterstaat to ESRI, based on AHN2. http://www.arcgis.com/home/item.html?id=58a541efc59545e6b7137f961d7de883
AHN DSM DSM 0.5m by 0.5m, 1m by 1m, or 2.5m by 2.5m, depending on selected options. Raw data from Actuele Hoogte Bestand http://www.arcgis.com/home/item.html?id=55df27e20c0d42e3a8bd48bc74c5c8cc (AHN2) or http://www.arcgis.com/home/item.html?id=b87c68ea246c4b17807cdad486279a47 (AHN3)
AHN DTM DTM 0.5m by 0.5m, 1m by 1m, or 2.5m by 2.5m, depending on selected options. Interpolated (surface level) data based on Actuele Hoogte Bestand http://www.arcgis.com/home/item.html?id=9d62ff8889ba41b2b712a68c7493bd16 (AHN2) or http://www.arcgis.com/home/item.html?id=9d62ff8889ba41b2b712a68c7493bd16 (AHN3)
Features Presence of features of the built environment https://www.pdok.nl/introductie/-/article/basisregistratie-grootschalige-topografie-bgt- (BGT) or https://www.pdok.nl/introductie/-/article/basisregistratie-topografie-brt-historie (Top10NL)

DTM (Terrain height)

  • 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 Construction's footprint polygon. 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 up 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 DTM. Instead, they are stored as properties of the Constructions in the Project.

Water

In locations with water features, the water's depth is "carved" into the DTM as determined up to this point. The following parameters are used to do so:

Starting from the edges of the polygon of the water feature, 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 depth relative to the DTM. This means that thin waterrways 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)

This section is a stub.

How-to's

See also

Changing terrain height

There are two options to change terrain height. One is to import a raster file with the new terrain height and the other option is to draw in the Tygron Platform where the terrain should be changed and to which height.

Importing a terrain height dataset

See how to import terrain height data.



Drawing terrain height

Editor → Current Situation (Ribbon tab) → Terrain (Ribbon bar) → Edit elevation model (Dropdown)
How to change terrain height:
  1. Open the Terrain Height Brush Panel
  2. Select "Start Drawing"
  3. Adjust the Radius and Press sliders as desired
  4. Select the brush type Raise, Flatten or Lower
  5. Adjust terrain height by pressing and holding the left mouse button while drawing in the 3D world
  6. Confirm the changes by selecting "Apply changes"


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