Wednesday, April 30, 2014

10.2.x - Getting Data Extents as Feature Classes (4 Methods)

Over the past couple of years, I have posted many posts on creating polygon extents from data.  Today, I am going to provide 4 ways to get the extent of a polygon.
  1. Use the 'Minimum Bounding Geometry' tool to create 'ENVELOPE' geometry types with or without the 'Group Option'.  This tool is available at the 'Advanced' level, so if you don't know how to/want to use python, this is your go to option to use.  The output is a feature class.
  2. For whole feature class extent use the arcpy.Describe(), and write it out to disk
    import arcpy
    from arcpy import env
    env.overwriteOutput = True
    fc = r"c:\States.shp"desc = arcpy.Describe(fc)
    extent = desc.extent
    pts = [arcpy.Point(extent.XMin, extent.YMin),
           arcpy.Point(extent.XMax, extent.YMin),
           arcpy.Point(extent.XMax, extent.YMax),
           arcpy.Point(extent.XMin, extent.YMax)]
    array = arcpy.Array(items=pts)
    poly = arcpy.Polygon(array)
    
    arcpy.CopyFeatures_management(poly, r"%scratchgdb%\way1")
    
  3. Method 1 for individual features: Use a cursor with extent XMin, YMin, XMax, and YMax, and arcpy.CreateFeatureClass()
    import arcpy
    from arcpy import env
    env.overwriteOutput = True
    fc = r"c:\States.shp"
    out_fc = r"%scratchgdb%\way2"
    if not arcpy.Exists(out_fc):
        arcpy.CreateFeatureclass_management(out_path="%scratchgdb%",
                                            out_name="way2", geometry_type="POLYGON",
                                            spatial_reference=arcpy.SpatialReference(4326))
    icur = arcpy.da.InsertCursor(out_fc, "SHAPE@")
    with arcpy.da.SearchCursor(fc, "SHAPE@") as rows:
        for row in rows:
            extent = row[0].extent
            pts = [arcpy.Point(extent.XMin, extent.YMin),
                   arcpy.Point(extent.XMax, extent.YMin),
                   arcpy.Point(extent.XMax, extent.YMax),
                   arcpy.Point(extent.XMin, extent.YMax)]
            array = arcpy.Array(items=pts)
            poly = arcpy.Polygon(array)
            icur.insertRow([poly])
            del array
            del poly
            del pts
            del extent
            del row
    
  4. Method 2 for individual features: Use a cursor objects and arcpy.CopyFeatures()
    import arcpy
    from arcpy import env
    env.overwriteOutput = True
    fc = r"c:\States.shp"
    out_fc = r"%scratchgdb%\way3"
    with arcpy.da.SearchCursor(fc, "SHAPE@") as rows:
        polys = []
        array = arcpy.Array()    
        for row in rows:
            extent = row[0].extent
            array.add(extent.lowerLeft)
            array.add(extent.lowerRight)
            array.add(extent.upperRight)
            array.add(extent.upperLeft)
            array.add(extent.lowerLeft)
            polys.append(arcpy.Polygon(array))
            array.removeAll()
            del row
        del array
        arcpy.CopyFeatures_management(polys, out_fc)
        del polys
    
Here are 4 examples on how to create extents using python or the built in system tools in ArcToolbox.
 Enjoy

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