ArcPy – Get Shortest Distance Between Two Geometries

arcpydistancegeometry

I'm using ArcPy and using a cursor to step through one polygon feature class. For each of these 'source' polygons, I am creating a SearchCursor to find all polygons in a second feature class that share a common attribute. For each of these matching polygons, I want to measure the distance between it and the search polygon. I also plan on measuring other geometry differences (to determine if it has just been shifted, rotated, scaled, etc).

The purpose of this work is to build up a change history between polygon datasets representing features at different times.

I've seen the ReturnDistance method mentioned in ArcObjects, but can't figure out how to run this using ArcPy. Is it possible, and if so, can anyone help with some rough sample code? If not, I'll probably resort to measuring the change in centroid position between the polygons.

Thanks, Steve

Best Answer

This answer is 3 years late so you've probably got a workaround by now. But for completeness, here's an arcpy method to measure the distance between 2 objects.

Geometry has a method distanceTo which:

Returns the minimum distance between two geometries. If the geometries intersect, the minimum distance is 0.

Both geometries must have the same projection.

Related Solutions

[GIS] Comparing two geometries in ArcPy

The issue is most likely one of floating point precision. In your case you've already extracted the geometries using arcpy, and you've matched them with your RUID.

Happily since you've got arcpy installed you've got numpy, which makes comparing sets of numeric arrays easy. In this case I'd suggest the numpy.allclose function, which is available in numpy 1.3.0 (installed with ArcGIS 10).

From the samples you gave above

geom1geoJSON = {'type': 'Polygon', 'coordinates': [[(-122.8423481559999, 47.060497293000083), (-122.84239755599992, 47.059262423000064), (-122.84416913599989, 47.059309693000046), (-122.84416913599989, 47.060497293000083), (-122.8423481559999, 47.060497293000083)]]}
geom2geoJSON = {'type': 'Polygon', 'coordinates': [[(-122.8423481559999, 47.060497293000083), (-122.84239755599992, 47.059262423000064), (-122.84416913599989, 47.059309693000046), (-122.84416913599989, 47.060497293000083), (-122.8423481559999, 47.060497293000083)]]}

import numpy as np

close = np.allclose(np.array(geom1geoJSON["coordinates"]), np.array(geom2geoJSON["coordinates"]), atol=1e-7)
#Returns True

The atol keyword specifies the tolerance value.

Note that you shouldn't use arcpy.AsShape at all. Ever. As I noted in this question (/shameless plug) there's a known bug in ArcGIS that truncates geometries when they are created without a coordinate system (even after setting the env.XYTolerance environment variable). In arcpy.AsShape there's no way to avoid this. Fortunately geometry.__geo_interface__ does extract the correct geometries from an existing geometries (though it doesn't handle complex polygons without the fix from @JasonScheirer ).

[GIS] Determine distance between two lines at multiple locations

If you convert your tracks to polygons (feature to polygons), you can then apply a negative buffer on all your track and it will remove the parts which are too narrow. Then you expand the resulting polygons again with a positive buffer of the same value and you compute the union between those two layers. You can then color code the result based on the attribute table (null values for the fields originated from the second layer means that it was too narrow)

EDIT: for more straight lines, you can erase the buffers where you have "not to narrow polygons" (green minus purple). This will yield convex rounded sides on your green polygons. You can fill this as a straight line using "minimum bounding geometry" for a convex hull, and intersect the convex hull with the original polygon layer.

I don't think that a measurement would be useful with this approach, but "minimum bounding geometry > rectangle by width" could help you in this case (after the union)

Best Answer

Related Solutions

[GIS] Comparing two geometries in ArcPy

[GIS] Determine distance between two lines at multiple locations

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