While measuring an angle in QGIS using measure angle tool, it is showing as 0 to 180 degree for clockwise direction and -1 to -179 for anticlockwise. What I need is, interior angle between vertices of irregular polygon. How should I calculate in QGIS?
http://anitagraser.com/2015/05/24/how-to-create-illuminated-contours-tanaka-style/ contains some way to do this:
First you split the lines/polygons into their atomic segments with v.split.
Then you calculate the azimuth for each of those features, see eg How to add Direction and Distance to attribute table? for the formula.
I don't know a better way but maybe there is.