Calculating X and Y of line start and line end using ArcPy?

Question

I have a series of polyline shapefiles and I am trying to automate the process of calculating the X and Y coordinates of the line start and line end using Python.

I have added the 4 fields (startx, starty, endx, endy) in Python with the following code:

Arcpy.addfield_management ("Polyline","startx","DOUBLE")

I can perform this task by right-clicking the attribute and calculating geometry, but I want to automate this process for about 30 polylines.

I have the following code I've found that might be able to perform the desired task with some modification:

xExpression = "float(!SHAPE.CENTROID!.split()[0])"
yExpression = "float(!SHAPE.CENTROID!.split()[1])"

arcpy.CalculateField_management("Polyline", "startx", xExpression, "PYTHON")
arcpy.CalculateField_management("Polyline", "starty", yExpression, "PYTHON")

This code only calculates the coordinate at the centre of the shape I believe. Are their any expressions I can add to this code to calculate the X and Y coordinates of the start and end points of the polyline?

I am using ArcGIS 10.1 with ArcInfo license.

Answer 1

I agree with Barbarossa that accessing the power of the da module would be beneficial. Here is very clean scripting approach:

import arcpy

fc = r'C:\Users\OWNER\Documents\ArcGIS\Default.gdb\samplePolyline'

fields = ['x1','x2','y1','y2']

# Add fields to your FC
for field in fields:
    arcpy.AddField_management(fc,str(field),"DOUBLE")

with arcpy.da.UpdateCursor(fc, ('x1','x2','y1','y2', "SHAPE@")) as cursor:
    for row in cursor:
        row[0] = row[4].firstPoint.X
        row[1] = row[4].lastPoint.X
        row[2] = row[4].firstPoint.Y
        row[3] = row[4].lastPoint.Y
        cursor.updateRow(row)

Answer 2

The field calcuation expression to do this is:

Start of line:

"!Shape!.positionAlongLine(0.0,True).firstPoint.X"
"!Shape!.positionAlongLine(0.0,True).firstPoint.Y"

End of line:

"!Shape!.positionAlongLine(1.0,True).firstPoint.X"
"!Shape!.positionAlongLine(1.0,True).firstPoint.Y"

Answer 3

I would loop through each polyline with arcpy.da.SearchCursor, reading the "SHAPE@" field. Then read the firstPoint and lastPoint from the polyline geometry.

Answer 4

I don't have experience coding but i modified one of the esri resources examples and it worked for me...

# Name: CalculateField_COORDINATES.py
# Description: Use CalculateField to calculate start and end points of a line

# Import system modules
import arcpy

try:
  # Set environment settings
  arcpy.env.workspace = "D:\SIG_MPIOS\MPIOS14.mdb"

  # Set local variables
  inFeatures = "RED_DISTRIBUCION"
  fieldName1 = "X_INI"
  fieldName2 = "X_FIN"
  fieldName3 = "Y_INI"
  fieldName4 = "Y_FIN"
  fieldPrecision = 18
  fieldScale = 11

  # Add fields
  arcpy.AddField_management(inFeatures, fieldName1, "DOUBLE",
                          fieldPrecision, fieldScale)
  arcpy.AddField_management(inFeatures, fieldName2, "DOUBLE",
                          fieldPrecision, fieldScale)
  arcpy.AddField_management(inFeatures, fieldName3, "DOUBLE",
                          fieldPrecision, fieldScale)
  arcpy.AddField_management(inFeatures, fieldName4, "DOUBLE",
                          fieldPrecision, fieldScale)

  # Calculate centroid
  arcpy.CalculateField_management(inFeatures, fieldName1,
                                "!shape.firstpoint.x!",
                                "PYTHON_9.3")
  arcpy.CalculateField_management(inFeatures, fieldName2,
                                "!shape.firstpoint.y!",
                                "PYTHON_9.3")
  arcpy.CalculateField_management(inFeatures, fieldName3,
                                "!shape.lastpoint.x!",
                                "PYTHON_9.3")
  arcpy.CalculateField_management(inFeatures, fieldName4,
                                "!shape.lastpoint.y!",
                                "PYTHON_9.3")
except Exception as e:
  # If an error occurred, print line number and error message
  import traceback
  import sys
  tb = sys.exc_info()[2]
  print("Line {0}".format(tb.tb_lineno))
  print(e.message)