A Ridge Valley Map is created from the input DEM. The Map itself is a 2-bit coded file with ridges that have a pixel value of 1 and are colored red. Valleys have a pixel value of 2 and are colored blue. Voids (NoData) have value-based NoData (the value being set to 3). The background is 0 and is colored tan.
Ridge / Valley posts are determined by calculating the height in relation to the surrounding posts using a 7 by 7 pixel kernel, ignoring the immediately adjacent posts. If the center post is in the top specified percent it is considered a ridge post. If the center post is in the bottom specified percent then it is considered a valley post.
|Left View shows a DEM, styled using the Relief Image Chain, right View shows the corresponding ridges (red) and valleys (blue)|
The technique was originally implemented for coarser resolution Digital Elevation Models (e.g. 30m pixel sizes). High resolution DEMs may require different kernel sizes and percentage settings.
Input DEM: Select a DEM file to use to create the ridge valley map
Input DEM NoData Value: If the Input DEM does not already have a NoData value (or mask) defined, the value to be considered as NoData should be entered here. DEfault is -32767.
Ridge Percent: Reports the surrounding height upper percentile ranking for post to be considered a ridge post. If the center post is in the top specified percent it is considered a ridge post.
Valley Percent: Surrounding height lower percentile ranking for post to be considered a valley post. If the center post is in the bottom specified percent then it is considered a valley post.
Ridge Valley Mask: Enter a filename for the output ridge valley map