1.6. EXPORTING GIS DATA:

Now we’ve defined the extents for our UE4 landscape, we need to export the GIS data into formats that can be imported in to UE4. We’ll start with the height map first, then we’ll export the aerial and vector data.

Height Map – Background Info:
  • UE4 needs a 16-bit greyscale image to use as a height map.
  • GM exports 16-bit images, but we need to scale the height values to the maximum range.
  • Maximum range of 16-bit values is 32768 (0 to 32767).
  • To scale our values across this range, we need to calculate the range of heights and the offset and adjust them for this.
  • It’s best to do this with a single tile so we’ll export the data to the right size first.
Step 1:

Select the area to export:

  • Click on the ‘Digitizer Tool’ and then click on the ‘AOI’ area feature you created earlier to select it.

Step 2:

Turn off aerial & vector layers:

  • Click the ‘Open Control Center’ icon.
  • Select the aerial and vector layers (not ‘User Created Features’)
  • Click ‘Hide Overlay’. (‘Hide Overlay’ changes to ‘Show Overlay’ when selected layers are hidden.)
Step 3:

Export a single tile (8,129px by 8,129px):

  • ‘File’ > ‘Export Elevation Grid Format…’
  • ‘Select Export Format’ = ‘GeoTiff’ then ‘OK’.
  • Choose ‘Elevation (32 bit floating point samples)’.
  • Change ‘Sample Spacing/Scale’ (‘X-axis’: = ‘1m’, ‘Y-axis’: = ‘1m’)
  • Check ‘Always Generate Square Pixels’.
  • Check ‘Generate TFW (World) File’.
  • Check ‘Generate PRJ File’.

On ‘Export Bounds’ Tab:

  • Check ‘Crop to Selected Area Feature(s)’.
  • Click ‘OK’.

In the ‘Save As’ window that appears:

  • Give it a useful filename and save it in a folder for working files.
  • Check the dimensions of the exported DTM GeoTiff file are 8,129px by 8,129px once it’s finished exporting.

[NOTE: UTM19 is the projection for the data (Universal Tranverse Mercator Zone 19), and NAD83 is the datum (North American Datum, 1983).]

Step 4:

Close the DTM tiles and load the 32-bit DTM GeoTiff you just exported.

  • Open the ‘Overlay Control Center’ in GM and select the DTM ‘.img’ file overlays.
  • Click ‘Close Overlay’.
  • Then find the DTM GeoTiff you exported earlier and drag it in to GM.
Step 5:

Next we need to determine the ‘Scale Factor’ and ‘Offset’ values.

  • In ‘Overlay Control Center’ select the 1m DTM file.
  • Click ‘Metadata…’ then record ‘Min Elevation’ and ‘Max Elevation’ values.
  • ‘Scale’ = 32767/(Max Elevation – Min Elevation) = 32767/(944.927-382.521) = 58.262
  • ‘Offset’ = -1 x (Min Elevation x Scale) = -1 x (382.521 x 58.262) = -22,286.438
Step 6:

The next step is to change the height range of the elevation data:

  • In the ‘Overlay Control Center’, select the 1m DTM file you previously exported.
  • Click Options (next to Meta Data)
  • On the ‘Alter Elevation Values’ tab, input the ‘Scale Factor’ and ‘Offset’, then ‘Apply’.
Step 7:

Export a 16-bit Greyscale Geo-Tiff:

  • ‘File’ > ‘Export Elevation Grid Format…’
  • ‘Select Export Format’ > ‘GeoTiff’
  • Check ‘Elevation (16 bit integer samples)
  • ‘Sample Spacing/Scale’ (‘X-axis’ = ‘1m’, ‘Y-axis’ = ‘1m’)
  • Check ‘Always Generate Square Pixels’.
  • Check ‘Generate TFW (World) File’.
  • Check ‘Generate PRJ File’.
  • Click ‘OK’.
  • Save it with a useful filename in a source data folder.
Step 8:

UE4 won’t read .tif (or Geo-Tiff) files, so we need to change the format to .png. For this we need Photoshop (or similar).

  • Launch Adobe Photoshop (or your preferred image editing software)
  • Load the 16bit GeoTiff you exported.
  • ‘File’ > ‘Save As…’
  • ‘Save as type: = ‘PNG (*.PNG;*.PNG)’
Aerial Imagery:
  • We’re using the aerial imagery to create masks for landscape surfaces and vegetation so we want to retain as much detail as possible.
  • As a result, at this stage we’re just seeking to export the aerial to the same extents as the height map.
  • We want a 24-bit Geo-tiff – a format we’ll be able to use in Photoshop.
Step 1:

Show the aerial imagery and hide DTM:

  • In ‘Overlay Control Center’, select the DTM, then ‘Hide  Overlay’
  • Then select the aerial files and ‘Show Overlay’.

[NOTE: The ‘User Created Features’ layer is showing and the ‘AOI’ area feature we created is selected (with the ‘Digitizer Tool’).]

Step 2:

Export the aerial:

  • ‘File’ > ‘Export Raster/Image Format…’
  • ‘Select Export Format’ > ‘GeoTiff’
  • Check ’24-bit RGB’.
  • ‘Sample Spacing/Scale’: (‘X-axis’: ‘1m’, ‘Y-axis’: ‘1m’)
  • Check ‘Always Generate Square Pixels’.
  • Check ‘Generate TFW (World) File’.
  • Check ‘Generate PRJ File’.
Step 3:

On the ‘Export Bounds’ tab:

  • Check ‘Crop to Selected Area Feature(s)’.
  • Click ‘OK’.
  • Save with useful filename.
Vector Data:
  • We want to keep the rail, road and trail vectors separate so we need to export them individually.
  • We’ll start with the rail vectors.
Step 1:

Show the rail vectors aerial imagery and hide DTM:

  • In ‘Overlay Control Center’, hide the aerial images and show the rail vector overlay.
  • The ‘User Created Features’ layer is still showing and the ‘AOI’ area feature is selected (‘Digitizer Tool’).
Step 2:

Export the rail vectors:

  • ‘File’ > ‘Export Vector Format…’
  • ‘Select Export Format’ > ‘Shapefile’
  • On the ‘File Selection’ tab of ‘Shapefile Export Options’ check ‘Export Lines’.
  • A ‘Save As’ window will appear – navigate to your exports folder and give the file a useful name.
  • Click ‘Save’ to return to the ‘Shapefile Export Options’ window.
Step 3:

Set the AOI as export bounds:

  • On the ‘Export Bounds’ tab check ‘Crop to Selected Area Feature(s)’
  • Hit ‘OK’ to export the rail vectors file.
Step 4:

Repeat Steps 1 to 3 for the road and trails vector files.

Your exported data folder should look something like this: