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karimbahgatkarimbahgat
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Don't ignore invalid polygon shapes in geo interface
Interpret orphan holes as exteriors. If only interior holes found, assume wrong winding order and return as exteriors.
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+61
-17
lines changed

2 files changed

+61
-17
lines changed

‎shapefile.py‎

Lines changed: 20 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -281,7 +281,7 @@ def organize_polygon_rings(rings):
281281
if bbox_overlap(hole_bbox, ext_bbox):
282282
hole_exteriors[hole_i].append( ext_i )
283283

284-
# then, for holes with more than one possible exterior, do more detailed hole-in-ring test
284+
# then, for holes with still more than one possible exterior, do more detailed hole-in-ring test
285285
for hole_i,exterior_candidates in hole_exteriors.items():
286286

287287
if len(exterior_candidates) > 1:
@@ -305,37 +305,42 @@ def organize_polygon_rings(rings):
305305
ext_i = sorted(exterior_candidates, key=lambda x: abs(signed_area(exteriors[x])))[0]
306306
hole_exteriors[hole_i] = [ext_i]
307307

308+
# check for holes that are orphaned (not contained by any exterior)
309+
orphan_holes = []
310+
for hole_i,exterior_candidates in list(hole_exteriors.items()):
311+
if not exterior_candidates:
312+
warnings.warn('Shapefile shape has invalid polygon: found orphan hole (not contained by any of the exteriors); interpreting as exterior.')
313+
orphan_holes.append( hole_i )
314+
del hole_exteriors[hole_i]
315+
continue
316+
308317
# each hole should now only belong to one exterior, group into exterior-holes polygons
309318
polys = []
310319
for ext_i,ext in enumerate(exteriors):
311320
poly = [ext]
312321
# find relevant holes
313322
poly_holes = []
314323
for hole_i,exterior_candidates in list(hole_exteriors.items()):
315-
# ignore any hole that is orphaned (not contained by an exterior)
316-
if not exterior_candidates:
317-
warnings.warn('Shapefile shape has invalid polygon: found orphan hole (not contained by any of the exteriors); ignoring.')
318-
del hole_exteriors[hole_i]
319-
continue
320-
# ignore any hole that is ambiguous (more than one possible exteriors)
321-
# this shouldn't happen however, since ambiguous exteriors are resolved
322-
# in the previous stage as the one with the smallest area.
323-
if len(exterior_candidates) > 1:
324-
warnings.warn('Algorithm error: algorithm was unable to resolve hole exterior among multiple possible candidates; ignoring.')
325-
del hole_exteriors[hole_i]
326-
continue
324+
327325
# hole is relevant if previously matched with this exterior
328326
if exterior_candidates[0] == ext_i:
329327
poly_holes.append( holes[hole_i] )
330328
poly += poly_holes
331329
polys.append(poly)
332330

331+
# add orphan holes as exteriors
332+
for hole_i in orphan_holes:
333+
poly = [holes[hole_i]]
334+
polys.append(poly)
335+
333336
return polys
334337

335338
# no exteriors, bug?
336339
else:
337-
raise Exception('Shapefile shape has invalid polygon: no exterior rings found (must have clockwise orientation)')
338-
340+
warnings.warn('Shapefile shape has invalid polygon: no exterior rings found (must have clockwise orientation); interpreting holes as exteriors.')
341+
exteriors = holes # could potentially reverse their order, but in geojson winding order doesn't matter
342+
polys = [[ext] for ext in exteriors]
343+
return polys
339344

340345
class Shape(object):
341346
def __init__(self, shapeType=NULL, points=None, parts=None, partTypes=None):

‎test_shapefile.py‎

Lines changed: 41 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -10,8 +10,7 @@
1010
# our imports
1111
import shapefile
1212

13-
# define valid shape tuples of (type, points, parts indexes, and expected geo interface output)
14-
# test all sorts, incl no holes, hole in singlepoly, hole in multipoly, nested holes and polys
13+
# define various test shape tuples of (type, points, parts indexes, and expected geo interface output)
1514
geo_interface_tests = [ (shapefile.POINT, # point
1615
[(1,1)],
1716
[],
@@ -127,6 +126,46 @@
127126
],
128127
]}
129128
),
129+
(shapefile.POLYGON, # multi polygon, holes incl orphaned holes (unordered), should raise warning
130+
[(1,1),(1,9),(9,9),(9,1),(1,1), # exterior 1
131+
(11,11),(11,19),(19,19),(19,11),(11,11), # exterior 2
132+
(12,12),(14,12),(14,14),(12,14),(12,12), # hole 2.1
133+
(15,15),(17,15),(17,17),(15,17),(15,15), # hole 2.2
134+
(95,95),(97,95),(97,97),(95,97),(95,95), # hole x.1 (orphaned hole, should be interpreted as exterior)
135+
(2,2),(4,2),(4,4),(2,4),(2,2), # hole 1.1
136+
(5,5),(7,5),(7,7),(5,7),(5,5), # hole 1.2
137+
],
138+
[0,5,10,15,20,25,30],
139+
{'type':'MultiPolygon','coordinates':[
140+
[ # poly 1
141+
[(1,1),(1,9),(9,9),(9,1),(1,1)], # exterior
142+
[(2,2),(4,2),(4,4),(2,4),(2,2)], # hole 1
143+
[(5,5),(7,5),(7,7),(5,7),(5,5)], # hole 2
144+
],
145+
[ # poly 2
146+
[(11,11),(11,19),(19,19),(19,11),(11,11)], # exterior
147+
[(12,12),(14,12),(14,14),(12,14),(12,12)], # hole 1
148+
[(15,15),(17,15),(17,17),(15,17),(15,15)], # hole 2
149+
],
150+
[ # poly 3 (orphaned hole)
151+
[(95,95),(97,95),(97,97),(95,97),(95,95)], # exterior
152+
],
153+
]}
154+
),
155+
(shapefile.POLYGON, # multi polygon, exteriors with wrong orientation (be nice and interpret as such)
156+
[(1,1),(9,1),(9,9),(1,9),(1,1), # exterior with hole-orientation
157+
(11,11),(19,11),(19,19),(11,19),(11,11), # exterior with hole-orientation
158+
],
159+
[0,5],
160+
{'type':'MultiPolygon','coordinates':[
161+
[ # poly 1
162+
[(1,1),(9,1),(9,9),(1,9),(1,1)],
163+
],
164+
[ # poly 2
165+
[(11,11),(19,11),(19,19),(11,19),(11,11)],
166+
],
167+
]}
168+
),
130169
]
131170

132171
def test_empty_shape_geo_interface():

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