Get a point on a polyline from end points given distance along poly line

Question

I have start point and end point of a polyline. How can I get a point on that polyline from end points specified by the given distance.

How can I get this by using arcpy provided that this script should work on ArcView without importing any modules (Like this answer). I'm trying not to hard code values.

Related Question:

• How to create a point along a line given distance
• How to interpolate points along a line in Python for ArcGIS 9.3?

Answer 1

This sounds similar to "Linear Referencing" and that toolset would be available in ArcView. Additionally, you can script this tool very easily.

Link to ESRI Help for Linear Referencing

Answer 2

Based on your needs, as @LouisH referred to, using Linear Referencing is definitely the way to go. I cobbled together some code that should meet your need of not hard-coding elements, but instead requesting them as parameters.

As explanation, the Linear referencing tool used below takes "Routes", in your case the line features, and places "Events", in your case the points, along them based on a distance field. This results in a FeatureLayer, which is stored in memory, which is the reason for the last function which copies the features to an output featureclass.

import arcpy
import os
from arcpy import env

#Working directory
wkspace        = arcpy.GetParameterAsText(0)
#Line feature class
rtecls         = arcpy.GetParameterAsText(1)
#Line Unique ID
rtecls_ID      = arcpy.GetParameterAsText(2)
#Table of points to be located
pnttbl         = arcpy.GetParameterAsText(3)
#Field in point table that references line point will be located along
pttbl_rteid    = arcpy.GetParameterAsText(4)
#Distance field in point table
pttbl_dst      = arcpy.GetParameterAsText(5)
#Output Layer, layer is stored in memory.  Features still need to be copied to feature class saved to disk
outlayer       = arcpy.GetParameterAsText(6)
#Output Feature Class - If shapefile, make sure to include ".shp" at the end.
outclass       = arcpy.GetParameterAsText(7)

#Type of feature being located
fttype = "POINT"

#Set Workspace
env.workspace = wkspace

#Build String for input parameters in Linear Referencing tool
pt_props = pttbl_rteid + " " + fttype + " " + pttbl_dst

#Output featureclass path
outfclass = wkspace + os.sep + outclass

# Execute MakeRouteEventLayer
arcpy.MakeRouteEventLayer_lr (rtecls, rtecls_ID, pnttbl, pt_props, outlayer)

#Save feature layer to feature class on disk
arcpy.CopyFeatures_management(outlayer, outfclass)

Edit - One thing to think about with this tool, and likely any operation to locate points based on the distance from the end of a line, is which end of the line you will start from. The linear referencing tool, for instance, works based on the digitized direction of a line. It will be important to ensure that you have some way of identifying which endpoint your measurements are based upon.

Answer 3

Solving a linear reference problem like this without importing any modules is beyond my range..

I have used Shapely(python package for manipulation and analysis of 2D geospatial geometries. And it is BSD licenced :-) )

download it from here . The 2.6 version which is the only one that supports arcgis 10 arcpy..It is a simple installation(1.5 MB size)

and now here is the arcpy script to achieve the purpose.. forgive my python..only today i learned about the loops, tuples etc :)

import arcpy
import math
from arcpy import env

env.workspace = r"C:\testshape"

desc = arcpy.Describe("Rivers.shp")
shapefieldname = desc.ShapeFieldName

rows = arcpy.SearchCursor("Rivers.shp")

temptup = ()

# get ESRI geometries out of their cage..
for row in rows:

    feat = row.getValue(shapefieldname)
    partnum = 0
    for part in feat:
        for pnt in feat.getPart(partnum):
            if pnt:
                temptup += ((pnt.X, pnt.Y),)
            else:
                print "Interior Ring:"
        partnum += 1    

# and now the shapely magic :)

import shapely
from shapely.geometry import LineString
lnstr = LineString(temptup)
rsltPoint = lnstr.interpolate(0.5)
print(rsltPoint.x,rsltPoint.y)

note : this will not work if the feature has curve segments

Answer 4

Might be an overkill, but if you have access to Network Analysis extension you could create network from your polylines and then create service areas around your input points, specifying SA size as the distance of interest. Here is a cursory example with 111 meters SA from the point:

Then you would have to find points where SA crosses the line.

Answer 5

i think you can get it with Feature Vertices To Points (Data Management) method. you can get more info here.

or you can check out Split Line At Point (Data Management) here.

they are not enough entirely but you can write your own code...

i hope it helps you...