Direction of Input ID to Target ID layers in QGIS [duplicate]

Question

I've got a distance matrix with entities with an Input ID, target ID, and distance. I'm looking for a way to find out the relative direction of the input ID columnn to the target ID column.

Question has been answered and works, but this question has alternative solutions for anyone who is looking for a similar process.

Answer 1

This became a little bit convoluted but it seems to be working.

For each pair of points azimuth is calculated then translated into directions (N, E ,S or W)

Change layer and field names to match your data:

dm = QgsProject.instance().mapLayersByName('Distance matrix')[0]
pointlyr1 = QgsProject.instance().mapLayersByName('ns_point')[0] #Input point layer in distance matrix
pointlyr1_idfield = 'ogc_fid'
pointlyr2 = QgsProject.instance().mapLayersByName('js_point')[0] #Target 
pointlyr2_idfield = 'ogc_fid'

new_field_name = 'Direction' #Add this text field to distance matrix before executing the code

dms = [[int(f['InputID']),int(f['TargetID'])] for f in dm.getFeatures()] #List all input and target ids
p1dict = {int(f[pointlyr1_idfield]):f.geometry() for f in pointlyr1.getFeatures()} #Create a dictionary of id and geometry for input
p2dict = {int(f[pointlyr2_idfield]):f.geometry() for f in pointlyr2.getFeatures()} #Same for target

directions = [] #List to hold directions (N,E,S,W)

for id1, id2 in dms:
    #For each pair of points calculate azimuth (-180 - +180)
    az = p1dict[id1].asPoint().azimuth(p2dict[id2].asPoint())
    def calcdir(a):
        #Translate azimuth to compass direction
        if -45<a<45:
            v = 'N'
        elif 45<=a<135:
            v = 'E'
        elif 135<=a<=180 or -180<=a<=-135:
            v = 'S'
        else:
            v = 'W'
        return v
    directions.append(calcdir(az))
#Write directions list to a column in Distance matrix layer
with edit(dm):
    for feat, direct in zip(dm.getFeatures(), directions):
        #print(feat.id(), direct)
        feat.setAttribute(feat.fieldNameIndex(new_field_name), direct) 
        dm.updateFeature(feat)