How to create a heightmap for a new neighbourhood

This how-to describes how to create a new height map for a new neighbourhood. Usually, when a new neighbourhood is designed, the height of the current situation has to be adjusted. The steps to get from the current height map to the new height map are described.

The existing situation, or the area where the new neighbourhood is planned, has a height. In Tygron Platform, this height is loaded by default. For this, the Tygron Platform uses the latest AHN. The layout of the area is loaded into the Tygron Platform using the BAG, the BGT, and for the terrain, the BRO.

The new situation has its own new layout. In this example, we assume that a design has been created. For the different components of the design, a height adjustment has been chosen in relation to the existing ground level. In this example, the following classification has been made:

- Houses = 0.30 m + ground level;
-Roads = 0.15 m + ground level;
-Gardens = 0
-Green structure = 0.15 m – ground level
-Water = 0.3 m – ground level

Preprocessing of the design drawing

How to preprocess the design drawing:

1. In QGIS, the DXF file is converted to a GeoJSON. This results in:
   Points;
   Lines;
   Surfaces.
2. Two additional attributes are added to the surfaces, namely:
   Hoogte_tov_mv (Height_relative_to_ground_level). This attribute represents the relative elevation of this surface. The value of this surface is derived from the design principles.
   Verhoging (Elevation). This attribute is used to visualize the project area. This attribute is assigned the value 1.

Creating the project boundary in Tygron

How to create the project boundary in Tygron:

1. Import the design drawing into Tygron as an Area. Here, you load all surfaces from the design drawing that fall within the project boundary. Make sure to base the area names on a logical name from the GeoJSON.
2. Then group the areas based on the common attribute, namely Hoogte_tov_mv.
3. Using a Distance Overlay, this area is converted into a grid. We call this Grid_Project_Area. We use the following settings:
   Select Input:
   Attribute: Specific layer
   Areas
   Attribute:
   Verhoging (Elevation)

Creating the height map for the groundworks map

How to create the heigth map for the groundworks map:

1. Add a Heightmap Overlay (DTM). We call this Height_Map.
2. Secondly, create a filter for the existing waterways. This is done by adding an Average Overlay, which we call Water_Filter. We use the following settings:
   Select Input: 1 Timeframe:
   Attribute: Specific layer;
   Terrains
   Cell averaging distance (m):
   1
   Attribute:
   Water
3. The cells with "water" are converted to a **NO_DATA** value. This is done using a Combo Overlay, which we call Water_no_data. We use the following settings:
   Grid Overlay A: 1 Timeframe
   Water_filter
   Grid Overlay B: 1 Timeframe
   Height_Map
   Formula:
   IF (GT(A,0), NO_DATA, B)
4. Next, the ditches are closed by replacing the NO_DATA values of the grid with the heights from the immediate surroundings (slope). This is done using an Average Overlay, which we call Ditches_Closed. We use the following settings:
   Select Input: 1 Timeframe:
   Grid: input Overlay;
   Water_no_data
   Cell averaging distance (m):
   10
5. A cutout of the closed waterways is created for only the project area. This is done using a Combo Overlay, which we call Height_Map_Groundworks . We use the following settings:
   Grid Overlay A: 1 Timeframe
   Project_Area
   Grid Overlay B: 1 Timeframe
   Ditches_Closed
   Formula:
   IF (GTE(A,0), B, NO_DATA)
6. Next, the Height_Map_Groundworks is set as the parent of the overlays mentioned in steps 1 to 4.
7. Finally, the **Height_Map_Construction_Ready** is exported as a grid. To verify the success of this operation, the height map can be further examined in QGIS.