Arcview 10.0 Cannot create Polygon with hole in Python. Impossible????

Question

Kim Ollivier a couple of years ago gave example Python code to create a polygon with a hole in it. This involved a null point between the outer and inner rings of data.

His particular example works, but when I try to input my realworld xy coords using the exact same methodology, I get the null point interpreted as a valid point at the x,y origin (0,0), which in UTM zone 31 is on the Equator, not correct.

Cannot use Erase(analysis), you need ArcInfo for that.

Anyone with any constructive advice to get round this particular brick wall, greatly appreciated.

Rob Pearce
Gardline Geosurvey

KimOllivier · Answer

It sounds more like an edge problem than a donut problem. If you are using a projection there is a lot of validation and clipping going on behind the scenes that may be deleting your 0,0 point.

Could you try making a point at (0.001,0.001) to see if that works?

You also have to be careful to add the points in the expected clockwise order for the outer ring and anticlockwise for the donut ring.
Running RepairGeometry afterwards cleans up these issues, so it might be there, but just not drawing.

The help for this tool is useful to browse to see a simple list of topology rules that you need to be aware of when writing a polygon from source coordinates.

curtvprice · Answer

Kim Ollivier a couple of years ago gave example Python code to create a polygon with a hole in it. This involved a null point between the outer and inner rings of data.

The help does not go into detail on this; though there is a deprecated script tool Create Features From Text File, from the Samples Toolbox, which supports creation of donut holes (Inner Rings).

Since this script is such a good short and detailed example for writing geometry, and tricky to locate in the install folder, I just went ahead and pasted it here, so people can find it in the forums when search for how to write polygons with donut holes or other geometry.
'''----------------------------------------------------------------------------------
 Tool Name:     CreateFeaturesFromTextFile
 Source Name:   CreateFeaturesFromTextFile.py
 Version:       ArcGIS 9.1
 Author:        Environmental Systems Research Institute Inc.
 Required Argumuments:  An Input Text File containing feature coordinates
                        An Input Character designating the decimal separator used in the text file.
                        An output feature class
 Optional Arguments:    A spatial reference can be specified.  This will be the
                        spatial reference of the output fc.
 Description:   Reads a text file with feature coordinates and creates a feature class
                 from the coordinates.
----------------------------------------------------------------------------------'''

import string, os, sys, locale, arcgisscripting
gp = arcgisscripting.create()
gp.overwriteoutput = 1

msgErrorTooFewParams = "Not enough parameters provided."
msgUnknownDataType = " is not a valid datatype. Datatype must be point, multipoint, polyline or polygon."
msgErrorCreatingPoint = "Error creating point %s on feature %s"

# sets all the point properties
def createPoint(point, geometry):
    try:
        point.id = geometry[0]
        point.x = geometry[1]
        point.y = geometry[2]
        # When empty values are written out from pyWriteGeomToTextFile, they come as 1.#QNAN
        # Additionally, the user need not supply these values, so if they aren't in the list don't add them
        if len(geometry) > 3:
            if geometry[3].lower().find("nan") == -1: point.z = geometry[3]
        if len(geometry) > 4:
            if geometry[4].lower().find("nan") == -1: point.m = geometry[4]
        return point
    except:
        raise Exception, msgErrorCreatingPoint

try:
    # get the provided parameters
    inputTxtFile = open(gp.getparameterastext(0))
    fileSepChar = gp.getparameterastext(1)
    outputFC = gp.getparameterastext(2)

# spatial reference is optional
    outputSR = gp.getparameterastext(3)

# make sure the text type specified in the text file is valid.
    inDataType = inputTxtFile.readline().strip().lower()
    dataTypes = ["point", "multipoint", "polyline", "polygon"]
    if inDataType.lower() not in dataTypes:
        msgUnknownDataType = "%s%s" % (inDataType, msgUnknownDataType)
        raise Exception, msgUnknownDataType

# create the new featureclass
    gp.toolbox = "management"
    gp.CreateFeatureclass(os.path.split(outputFC)[0], os.path.split(outputFC)[1], inDataType, "#", "ENABLED", "ENABLED", outputSR)
    # create a new field to assure the id of each feature is preserved.
    idfield = "File_ID"
    gp.addfield(outputFC, idfield, "LONG")
    # get some information about the new featureclass for later use.
    outDesc = gp.describe(outputFC)
    shapefield = outDesc.ShapeFieldName
    # create the cursor and objects necessary for the geometry creation
    rows = gp.insertcursor(outputFC)
    pnt = gp.createobject("point")
    pntarray = gp.createobject("Array")
    partarray = gp.createobject("Array")
    
    locale.setlocale(locale.LC_ALL, '')
    sepchar = locale.localeconv()['decimal_point']
    
    # loop through the text file.
    featid = 0
    lineno = 1
    for line in inputTxtFile.readlines():
        lineno += 1
        # create an array from each line in the input text file
        values = line.replace("
", "").replace("", "").replace(fileSepChar, sepchar).split(" ")

# for a point feature class simply populate a point object and insert it. 
        if inDataType == "point" and values[0].lower() != "end":
            row = rows.newrow()
            pnt = createPoint(pnt, values)
            row.SetValue(shapefield, pnt)
            row.SetValue(idfield, int(values[0]))
            rows.insertrow(row)

# for a multipoint the text file is organized a bit differently.  Groups of points must be inserted at the same time.
        elif inDataType == "multipoint":
            if len(values) > 2:
                pnt = createPoint(pnt, values)
                pntarray.add(pnt)
            elif (len(values) == 2 and lineno != 2) or values[0].lower() == "end":
                row = rows.newrow()
                row.SetValue(shapefield, pntarray)
                # store the feature id just in case there is an error. helps track down the offending line in the input text file.
                if values[0].lower() != "end":
                    row.SetValue(idfield, featid)
                    featid = int(values[0])
                else:
                    row.SetValue(idfield, featid)
                rows.insertrow(row)
                pntarray.removeall()
            elif (len(values) == 2 and lineno == 2):
                featid = int(values[0])

# for polygons and lines.  polygons have a bit of logic for interior rings (donuts).
        # lines use the same logic as polygons (except for the interior rings)
        elif inDataType == "polygon" or inDataType == "polyline":
            #takes care of 
            #adds the point array to the part array and then part array to the feature
            if (len(values) == 2 and float(values[1]) == 0 and lineno != 2) or values[0].lower() == "end":
                partarray.add(pntarray)
                row = rows.newrow()
                row.SetValue(shapefield, partarray)
                # store the feature id just in case there is an error. helps track down the offending line in the input text file.
                if values[0].lower() != "end":
                    row.SetValue(idfield, featid)
                    featid = int(values[0])
                else:
                    row.SetValue(idfield, featid)
                rows.insertrow(row)
                partarray.removeall()
                pntarray.removeall()
            #adds parts and/or interior rings to the part array
            elif (len(values) == 2 and float(values[1]) > 0) or values[0].lower() == "interiorring":
                partarray.add(pntarray)
                pntarray.removeall()
            #add points to the point array
            elif len(values) > 2:
                pnt = createPoint(pnt, values)
                pntarray.add(pnt)
            elif (len(values) == 2 and lineno == 2):
                featid = int(values[0])

inputTxtFile.close()
    del rows
    del row
    
except Exception, ErrorDesc:
    # handle the errors here. if the point creation fails, want to keep track of which point failed (easier to fix the
    # text file if we do)
    if ErrorDesc[0] == msgErrorCreatingPoint:
        if inDataType.lower() == "point":
            msgErrorCreatingPoint = msgErrorCreatingPoint % (values[0], values[0])
        else:
            msgErrorCreatingPoint = msgErrorCreatingPoint % (values[0], featid)
        gp.AddError(msgErrorCreatingPoint)
    elif ErrorDesc[0] != "":
        gp.AddError(str(ErrorDesc))

gp.AddError(gp.getmessages(2))

# make sure to close up the fileinput no matter what.
    if inputTxtFile: inputTxtFile.close()

Additional search keys: doughnut, polygon rings, writing polygon geometry