Module 8 - Working with Geometries

This week's lab used Python scripting to copy specific data variables from an existing polyline shapefile to a text file.

Screenshot of a portion of the printed text file.

The screenshot above shows the following variables extracted from a polyline shapefile (called "rivers.shp"): OID number, Vertex ID number, X coordinates, Y coordinates, and the part name. There are multiple values with the same OID and part name - that is because the polyline file contains an array of points that are connected together to form the polyline. So each part/OID number represents a vertex along each grouped polyline.

The script was short, but the syntax was a bit tricky to get the necessary variables to print correctly. In the end it was a matter of how many parenthesis were being used and recalling which variable was associated with each row called. A quick run down of the pseudocode used is as follows:

Start

    Import arcpy

    Set workspace environments

           Define workspace file path

           Enable overwriteOutput

           Define "fc" as "rivers.shp"

     Define "rivers.shp" variables to extract using SearchCursor

     Cursor in SearchCursor will look for data in the OID, SHAPE, and NAME fields

     Create text file

            Populate text file with rivers.shp data

            Define a vertex id variable

            For Search Cursor results, define the row:

                  For the Search Cursor row results.getPart():

                  print the OID, vertexid, (x, y coordinates), and NAME fields

                  write the OID, vertexid, (x, y coordinates), and NAME fields to the text file

      Close the text file

      Close the Search Cursor row

      Close the Search Cursor

END