Finding distance between point and polygon edge in eastward direction using PyQGIS?

Question

I need to find distance in eastward direction from each point to the closest polygon edge:

I can find shortest distance in any direction with:

pointlayer = QgsProject.instance().mapLayersByName('points_inter_squares')[0]
points = [[f.geometry(),f['Ruta_100km']] for f in pointlayer.getFeatures()]

squarelayer = QgsProject.instance().mapLayersByName('squares')[0]
squares = [[f.geometry(),f['Ruta_100km']] for f in squarelayer.getFeatures()]

for point in points:
    print(min([QgsGeometry.distance(point[0],square[0]) for square in squares if point[1]!=square[1]]))

>>12639.380321901293
>>3320.150455611874
>>6650.862023710273
>>2452.079442886869

'Ruta_100km' is the Squares IDs, so I measure distance to all Squares but the one intersecting the Points.

Is there a method where I can specify direction when measuring distance?

Answer 1

A general solution: Provided a grid described by its origin (x0, y0) and a grid spacing d_grid (100km in your example), the problem reduces to calculate the difference between the test points p = (x, y) x-coordinate and the x-coordinate of the N-S grid line lying next to p, x_square, so the question is, what is x_square:

The following does not need a grid layer, but only the description of the grid as described above:

for p in points:
    # assumption: grid origin (x0, y0), spacing d_grid
    # metric coordinate system
    y = p.geometry().asPoint().x()
    # calculate y-distance to origin
    dx0 = x - x0
    # calculate number of square in which p(x, y) lies (2 in the example)
    square_count = int(dx0 / d_grid) + 1
    # calculate x-coordinate of N-S grid line next to p
    x_square = x0 + d_grid * square_count
    # calculate the desired distance
    dp = x_square - x
    print(dp)

Answer 2

Based on the comment from @Michael Stimson I managed to solve this by creating a line extending east, intersecting this with the polygons, finding min x coord of the resulting line(s) and subtracting this minx-startx. It should also work with irregular shaped polygons. It requires having polygon ids on the points (for example by intersecting them) to exclude any polygon directly intersecting the point.

pointlayer = QgsProject.instance().mapLayersByName('points_inter_squares')[0]
points = [[f.geometry(),f['Ruta_100km']] for f in pointlayer.getFeatures()]

squarelayer = QgsProject.instance().mapLayersByName('squares')[0]
squares = [[f.geometry(),f['Ruta_100km']] for f in squarelayer.getFeatures()]

max_search_distance = 200000

for geom, pointid in points:
    startx, starty = geom.asMultiPoint()[0]
    endx = startx+max_search_distance
    line = QgsGeometry.fromPolyline([QgsPoint(startx,starty), QgsPoint(startx+max_search_distance,starty)])
    intersections = [QgsGeometry.intersection(line,square[0]) for square in squares if (pointid!=square[1] and QgsGeometry.intersects(line,square[0]))]
    minx = min([l.asPolyline()[0][0] for l in intersections], default=startx) #If no feature is found, set minx to startx which will give 0 distance when subtracting
    print(minx-startx)