Geodata

Run a simulation on terrain, surface and canopy height data from a site survey instead of the default global datasets.

Custom geodata replaces the default global elevation and vegetation data with data of the site itself, for example:

• A terrain map at 1 m resolution, in place of a global dataset at 30 m.

• A canopy height map of the season the simulation covers, rather than a single fixed one.

An uploaded file can be reused in any number of simulations.

Three types of data can be uploaded:

• ⛰️ Terrain (DTM) is the bare ground elevation.

• 🏢 Surface (DSM) is the ground including buildings etc.

• 🌳 Canopy height (CHM) is the height of the vegetation.

Uploading a file

1. Navigate to the Geodata tab and click “New Geodata”.

2. Drop the file onto Upload GeoTiff, or browse for it.

3. Enter a Name and choose the Type.

4. Tick Data meets specification.

5. Under Finalise geodata, click Mark as Final. A finalized entry can be attached to a simulation and can no longer be edited.

The form is saved while it is filled in, so it can be left and finalized later.

The Type decides how the values are read:

Type	Select	Values are
⛰️ Terrain	Digital Terrain Model	metres above sea level
🏢 Surface	Digital Surface Model	metres above sea level
🌳 Canopy height	Canopy Height Model	metres above the ground

Attaching geodata to a simulation

During simulation setup, open the Geodata section of the Site step and select the entries to be used.

A simulation takes at most one file of each type: one terrain, one surface and one canopy height file. Selecting a different file of the same type replaces the previous one, and a type that is not uploaded runs on the default dataset.

How custom geodata is used

An uploaded file does not replace the default datasets outright. Where the file has a value, that value is used. Everywhere else the default global dataset applies.

Two consequences follow:

• ✅ A file covering only part of the simulated area is fine. The remainder runs on the default data, with no gap and no error.

• ⚠️ A file covering none of the simulated area changes nothing, and the simulation runs entirely on the default data without warning.

Where custom geodata applies

Only the LES domains around the site take custom geodata. The meso domain surrounding them always runs on the default datasets.

Domain	Grid	Data used
LES	100 m and 40 m	Custom geodata where it has values, default datasets elsewhere
Meso	coarser, surrounding the site	Default datasets only

Preparing a file

A file has to meet four requirements.

Requirement	Needs to be
📁 Format	A GeoTIFF, with the extension .tif or .tiff, of at most 1.5 GB.
🌍 Coordinate reference system	Present. Any projection is accepted and is converted to the projection of the simulation, but a file without one cannot be placed on the map.
📏 Values	In metres: above sea level for terrain and surface, above the ground for canopy height.
🕳️ No-data value	Recorded in the GDAL_NODATA header tag, number 42113. Those pixels are treated as missing, and the default dataset fills them in.

The no-data value must be one that cannot occur as a real height. NaN is the safest choice where the file stores decimal values, and a value outside the physical range, such as -9999, works everywhere. Do not use 0, which is a valid measurement.