I am trying to build height labels for contour lines from the lines themselves. This is pretty straightforward since the height values are contained in the contour data and I can easily extract them with the Labeller.
The problem is that I want all the height labels to be rotated as if one was always reading them facing uphill. They currently come out of the Labeller facing both uphill and downhill. The labels follow the contour line as they should, all that is fine, my only issue is that I want to rotate some of them 180 degrees.
How can I use the neighbouring contour lines to detect what is uphill?
What is the best way to rotate the eronous labels based on the above direction?