ArcGIS Interpolation – How to Interpolate Points Along Line in Python

arcgis-9.3arcpylinear-referencing

I am building a Python geoprocessing script for ArcGIS 9.3. In the script, I have a simple LINE feature class with one row, one line.

How can I use a linear referencing system to interpolate a point along the path?

I can use a cursor to access the feature geometry, and get the vertex geometries. But I can't find anything that could help me interpolate points along it.

Note: this is ridiculously simple with Shapely:

import shapely.wkt
line = shapely.wkt.loads('LINESTRING (380 60, 360 130, 230 350, 140 410)')
line.interpolate(0.0).xy # (array('d', [380.0]), array('d', [60.0]))
line.interpolate(100.0).xy # (array('d', [346.16312174913622]), array('d', [153.41625550146173]))
# ... etc

line with point at 100 m

Is there any equivalent in ArcGIS?

I have all the common ArcGIS extensions to my disposal.

Or should I just bring the geometry over to Shapely to do the work?

The geometry processing needs to eventually go back to ArcGIS.

Best Answer

In case this is helpful to others, i was able to create the following python code using arcpy which will place points at a specified interval based on an input line feature layer.

import arcpy

line_lyr = 'my_line'
pt_lyr =  "my_point"
interval = 200

insertCursor = arcpy.da.InsertCursor(pt_lyr, ["SHAPE@XY"]) # this is the pre-existing pt feature class

with arcpy.da.SearchCursor(line_lyr, ['OID@','SHAPE@','NAME']) as searchCursor: # this is the line feature on which the points will be based
    for row in searchCursor:
        lengthLine = round(row[1].length) # grab the length of the line feature, i'm using round() here to avoid weird rounding errors that prevent the numberOfPositions from being determined
        if int(lengthLine % interval) == 0:
            numberOfPositions = int(lengthLine // interval) - 1
        else:
            numberOfPositions = int(lengthLine // interval)

        print "lengthLine", lengthLine
        print "numberOfPositions", numberOfPositions
        if numberOfPositions > 0: # > 0 b/c we don't want to add a point to a line feature that is less than our interval
            for i in range(numberOfPositions): # using range, allows us to not have to worry about
                distance = (i + 1) * interval
                xPoint = row[1].positionAlongLine(distance).firstPoint.X
                yPoint = row[1].positionAlongLine(distance).firstPoint.Y
                xy = (xPoint, yPoint)
                insertCursor.insertRow([xy])
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