[GIS] Updating polygon geometry: deleting inner rings with python

geometryogrpython

I've searched, but can't find clear explanations how can I simply delete inner rings from existing polygons with python or extract outter rings and overwrite the geometry. Seems GDAL/OGR should be the simplest, but still I need some help…

Simple vision of mine would be:

dataSrc=driver.Open(shp)
layer=dataSrc.GetLayer()
for i in xrange(layer.GetFeatureCount()):
    feature = layer.GetFeature(i)
    geometry = feature.GetGeometryRef()
    if geometry.GetArea()<200:
        layer.DeleteFeature(i)
    if geometry.GetGeometryCount()>1:
        geometry=geometry.GetGeometryRef(0) #overwrite geom, getting the first ring outer
        feature.SetGeometry(geometry)
        layer.SetFeature(feature)

geometry.Destroy()

This doesn't loop through, it's just how I would like to see.

As I know the first ring or the first part of the geometry should be the outer ring, so I assumed I can just ask for it like that.Suppose that's not a problem.

So, probably the question is just about Updating Geometry. I open dataset withouth specific- Reading or Writing, so I assume it should let me write in it not just read. But if I do not want to have a new dataset, can I just update write like that or i should anywhays better create a new dataset?

Or maybe there is even more simple way to solve this with python?

Best Answer

I've found the solution with arcgisscripting, if anyone gona need to automate it.

It's really simple,.. just required some time to catch those holes :)

rows=gp.UpdateCursor(shp) #everything is done with one Cursor, but couple of arrays
row=rows.Next()
try:
    while row:
        if row.shape.area < 200:  #it's just deleting small polygons
            rows.DeleteRow(row)
        else:                     #part of cleaning from inner rings (donuts)
            geom=row.shape
            array=geom.GetPart(0)
            pnt=array.Next()
            newarray = gp.CreateObject("Array") #writing geometry to newArray       
            while pnt:
                newarray.add(pnt)
                pnt=array.Next()
                newpnt=newarray.Next()
                if not pnt:                     #this is the HOLE! 
                    break                       #when detect - break the loop!
            row.shape=newarray
            rows.UpdateRow(row)
        row=rows.Next()

    del row
    del rows
except:
    gp.GetMessages()
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