How to use a WMS to estimate foliage (Heat Overlay)
Although the Heat Overlay's results can be greatly affected by the accuracy of the presence of foliage, the presence of trees may be difficult to ascertain directly from available data sources. It is possible to combine imaging data with some basic calculations to compute the likely presence of foliage in specific locations.
- Add a new WMS Overlay, with "Infrared" as its Project Source. This source is available by default.
- Select the most recent infrared layer.
- As result type, select the "Red" color channel.
- Add a Combo Overlay, and set Grid Overlay "A" to the created WMS Overlay with the Infrared Project Source.
- As formula for the Combo Overlay, enter "GT(A, 160)"
- Duplicate the WMS Overlay, and set the result type of the duplicate to the "Green" color channel.
- Add the second WMS Overlay to the Combo Overlay as Grid Overlay "B".
- Change the formula for the Combo Overlay to MUL(GT(A, 160), GT(B, 80),14)
- Add a Heat Overlay, and open its configuration wizard.
- Continue to the step regarding Foliage, and in that step opt to use a grid as input.
- As foliage input grid, select the configured Combo Overlay.
- The Heat Overlay now performs calculations using foliage which is derived from infrared imagery.
- This examples relies on the Infrared Project Source which is available by default, but only provides coverage in The Netherlands.
- This example does not produce a perfect result, but is intended as a demonstration for the parsing of WMS image data.
- The "Red" color channel is required as a threshold, as this example relies on an infrared datasource, which differs from human-perceived visual colors.