Extending rectangular polygon in one direction until it intersects with another polygon using Shapely

Question

Is there a way to extend polygons in Shapely? I have a scenario which looks as follows

What I would like to do is to extend the horizontal polygon to the vertical one.

The polygons exteriors are represented as follows:

vert_poly.exterior.xy

(array('d', [55.63234329223633, 517.281494140625, 517.281494140625, 55.63234329223633, 55.63234329223633]),
 array('d', [632.2301635742188, 632.2301635742188, 647.7040405273438, 647.7040405273438, 632.2301635742188]))

and

hor_poly.exterior.xy

(array('d', [560.3878784179688, 575.0977172851562, 575.0977172851562, 560.3878784179688, 560.3878784179688]),
 array('d', [64.83158111572266, 64.83158111572266, 904.9833984375, 904.9833984375, 64.83158111572266]))

Using vert_poly = vert_poly.buffer(vert_poly.distance(hor_poly)) returns

which is in right the direction, but not quite. This creates the ellipse-like shape around the rectangle. But what I would like to achieve is to extend the horizontal rectangle so that the two end points of it would connect with the vertical one.

Answer 1

My suggestion would be to use the

shapely.affinity.scale(geom, xfact=1.0, yfact=1.0, zfact=1.0, origin='center')

method. This can scale your horizontal polygon to your vertical. I would calculate the scaling factor using the object.bounds attribute which gives you a set of your outer limits (minx, miny, maxx, maxy). You can do this for both polygons and then calculate the scaling factor as:

hminx, hminy, hmaxx, hmaxy = hor_poly.bounds
vminx, hminy, hmaxx, hmaxy = vert_poly.bounds

xfact = (hmaxx-hminx)/(vminx-hmaxx)

hor_poly = scale(hor_poly, xfact=xfact)

Answer 2

Normally I would suggest over-enlarging the left polygon, call intersection(), and construct the new polygon from the returned points, but your question is so specific that you can work with coordinates.

General

Say your left rectangle is (X1,Y1),(X2,Y2) (top left/bottom right) and your right rectangle is (X3,Y3),(X4,Y4). Then the extended left rectangle is (X1,Y1),(X2,Y3).

Shapely

# let left, right be the given Polygons
extended_left = Polygon( [ left.bounds[:2], (right.bounds[0], left.bounds[1]), \
                          (right.bounds[0], left.bounds[3]), left.bounds[2:]  ] )