Create in memory polygon with RasterToPolygon

Question

I need to create a number of polygons in a loop from a raster. Essentially, the loop will call a function a number of times which needs to convert it to a polygon:

def myfunc(raster):

    #do some raster processing
    return arcpy.RasterToPolygon_conversion(raster, "in_memory\poly")

But the object it returns seemingly has nothing in it? The end result is I want to create a single shapefile from all the polygon features I will create. It seems silly to call RasterToPolygon, writing out a temporary shapefile for each polygon and then collecting them altogether as they will easily all fit in the RAM available.

Is there any way to output a Polygon geometry from RasterToPolygon ?. I.e, can I not do some thing like this:

poly = arcpy.RasterToPolygon_conversion(raster, arcpy.Polygon)

Answer 1

All Geo-Processing tools return a results object but many code samples don't show this. Your function is returning a results object because your code is assuming that it always executes without error. What your code should be is this:

res = arcpy.RasterToPolygon_conversion(raster,"in_memory/poly","NO_SIMPLIFY")

You can then query the results object to see if your code has executed, so something like:

if res.status == 4:
     arcpy.AddMessage("Conversion executed without error!")
else:
     # Burst into tears
     pass

Also your upload code is flawed as you keep overwriting in_memory/poly, you need to increment the "poly" featureclass name so you stack up all your polygons in memory then do your final merge. You can achieve the increment by having a global counter or you pass in a pre-computed featureclass name.

Answer 2

one thing is to watch out for your "in_memory\poly", that string should be made "raw" by adding an r-prefix, or the back-slash will be interpreted as an escape character:

 return arcpy.RasterToPolygon_conversion(raster, r"in_memory\poly")

or

return arcpy.RasterToPolygon_conversion(raster, "in_memory\\poly")

I usually like to just use a variable so I can easily refer to the in memory file later:

out_polygon = r"in_memory\poly"
arcpy.RasterToPolygon_conversion(raster, out_polygon)

Edit/Update 1: If you are running this logic in a loop, then you should create a list of polygon outputs and then a final append to get all raster-to-polygon outputs in on feature class. Something like:

intermediate_outputs = []
for i in range(0,len(rasters),1):
    out_poly = "in_memory/poly{}".format(i)
    arcpy.RasterToPolygon_conversion(raster, out_poly)
    intermediate_outputs.append(out_poly)

final_output = os.path.join(OUTPUT_WORKSPACE, 'vectorized_rasters')
arcpy.Append_management(intermediate_outputs, final_output, "TEST","","")

Answer 3

An answer to my question: You can create an arcpy.Geometry() object and pass this to RasterToPolygon...