ArcPy – Deleting Line Vertices Inside a Polygon using ArcGIS Desktop

Question

Is there a way to automatically delete vertices in line features using a polygon file in ArcGIS so that it wouldn't cut up the line but just straightens the line inside the polygon?

The lines are lines and the box represents a polygon that covers them. I want to delete line vertices that are inside the polygon so the line would be straight inside the polygon boundary like on the illustration.

I use ArcGIS 10.1 but have access to other software also if something offers the solution.

Answer 1

The key is the difference method on geometry objects. The following code is far from efficient, since a new update cursor is opened for each polygon. But it has the added benefit of supporting multiple polygons on the same line:

import itertools, arcpy
arcpy.env.overwriteOutput = True
line_FC = r'<path to lines>'
poly_FC = r'<path to polygons>'
output = r'<path to result>'

#clone input lines to memory for fast processing
temp = arcpy.CopyFeatures_management(line_FC, "in_memory/temp")

polygons = arcpy.CopyFeatures_management(poly_FC, arcpy.Geometry())

for poly in polygons:
    with arcpy.da.UpdateCursor(temp, ["SHAPE@"]) as uCursor:
        for line in uCursor:
            line = line[0]
            diff = line.difference(poly)
            #if the two lines are not equal, that means it intersected the polygon
            if not line.equals(diff):
                #the result of geometry.difference() is a multipart line of only those
                #parts that lie outside the polyon
                parts = diff.getPart()

                #if parts is empty that means the line is completely within the polygon
                #i.e., no difference
                if parts:
                    #We'll need to "join" the end of part1 to the beginning of part2
                    #so we'll just flatten the list of lists
                    joined = list(itertools.chain.from_iterable(parts))

                    #and create a new polyline object to update the shape
                    poly_trimmed = arcpy.Polyline(arcpy.Array(joined))
                    uCursor.updateRow([poly_trimmed])

arcpy.CopyFeatures_management(temp, output)

I haven't tested it with edge cases, but this should get you started.