Well, I’ve been on a bit of a hiatus from this blog, thanks in large part to switching jobs and cities. But, I’ll try to fit posts in here and there as time allows.
Since ArcGIS licenses come at a premium (i.e. not everyone gets one), I am often tasked with performing file conversions that are difficult to perform outside the ArcGIS environment (and without the help of arcpy). So, in my quest for efficency (or laziness, whichever you choose), I am attempting to write a script that will take polygon shapefiles, convert to one line shapefile, and output the lines to a GPX file for upload to a GPS unit. The ultimate goal is to use py2exe to make a standalone application in which users can upload their own polygon shapefile and output a GPX file, and leave me out of it (not that I mind, but I’d rather focus on analysis).
Here’s what I’ve got so far. It deconstructs a polygon shapefile to individual vertices and outputs a line shapefile, using the pyshp library. Next steps involve installing GDAL, figuring out how to convert the shapefile to GPX, and packaging it all up with py2exe for distribution.
# import the shapefile library import shapefile # path to input polygon shapefile infc = shapefile.Reader(r"C:\users\dwiens\GIS_Data\testpoly") # create a shapefile writer outfc = shapefile.Writer(shapefile.POLYLINE) # turn geometry/attribute autoBalanace on outfc.autoBalance = 1 # add a field, any field outfc.field('FIELD','C','1') # get the input geometries shapes = infc.shapes() # create empty arrays to hold line parts and vertices linePoints =  lineParts =  # loop through shapes for shape in shapes: # loop through each vertex for point in shape.points: # add each vertex to array linePoints.append(point) # add vertex array to shape array lineParts.append(linePoints) #empty the vertex array, move to next shape linePoints =  # encode coordinates as a line outfc.line(parts=lineParts) # add blank value as a record outfc.record('') # save the shapefile outfc.save(r"C:\users\dwiens\GIS_Data\testline")