Adding vertex set distance from first or last vertex in polyline?

Question

For ArcGIS 10.1, is there a python script or tool that will add only one vertex (node) a set distance from the first vertex, or alternatively, a set distance from the last vertex for multiple polylines? The original vertices need to be retained for each polyline.

I have over 500 polylines and creating vertices individually in an edit session is taking forever!

Answer 1

1. Create a copy of your lines
2. Run add geometry attributes on it, part count and length
3. Select ones with length > limit and part_Count=1
4. Open table, select field Shape, pick field calculator, parser Python, advanced

Use expression below:

def insertV(dist,shp):
 newP=shp.positionAlongLine (dist).firstPoint
 n,arr,part=0,arcpy.Array(),shp.getPart(0)
 m=len(part)
 for i in range(m):
  p=part.getObject(i); L=shp.measureOnLine(p)
  if L>dist:
   n+=1
   if n==1:arr.add(newP)
  arr.add(p)
 return arcpy.Polyline(arr)

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insertV(100, !Shape! )