Fastest Way to Parse Points in Polygon Feature Class?

Question

Hello everyone,

What is the fastest way to parse the points of a polygon feature class?  I have been using the IPolygon4 InteriorRingBag and ExteriorRingBag properties, and then looping through the point collections for interior/exterior rings.  It is ridiculously slow.

Any other suggestions?

JosephArmbruster · Answer

Using the IPointCollection for a polygon only makes sense if you do not have multipart geometry, since you can not tell where a part begins and ends.  If I do not care about the part-to-part relationships, I find the easiest way is to use the IGeometryCollection interface.  All you need to do is iterate from 0 to GeometryCount, get the geometry and then use the IPointCollection interface to obtain the individual points.  Like this:

IGeometryCollection geometries = polygon_feature.Shape as IGeometryCollection;
for(int i=0; i<geometries.GeometryCount; ++i)
{
  IPointCollection point_collection = geometries.Geometry as IPointCollection;
  // do something
}

IanMcCrorie · Answer

Hi,

Doing something very similar, looping exterior and interior rings. Only doing one feature at a time on finishing an edit and using this to create an SDOGeometry. Speed is not really an issue, using C# in ArcMap 9.1 (I know - ancient - but too much code to upgrade easily)

I have a problem though where the user has edited the shape using the Arc tool. At the end of the edit the only recorded vertices for the arc section of the polygon are the first and last points. Does anyone know an easy way to get the arc as a series of vertices? If edits are saved the arc section becomes a series of vertices but I don't want to have to save edits before accessing them.

Ian

EricPaitz · Answer

As far as I understand it using ArcObjects with .NET (VB.NET or C#.NET) there is a lot of interop between the COM world (ArcObjects) and the .NET world. This interop can have a negative effect on performance. One simple thing to try with your code example would be to not allocate any new memory or objects in the loops. I see several objects being declared in the loops, maybe try declaring everything outside the main loop and just reuse the variables inside the loop. This is a long shot but its something to try and at least rule out. I am not sure if there is much you can do to speed up the .NET code.

There is also a new Interface called IGeometryBridge and a structure called WKSPoint that might help. This link might help understand these new objects.
http://help.arcgis.com/en/sdk/10.0/arcobjects_net/conceptualhelp/index.html#//000100000363000000

This page titled "Performance of ArcObjects" is a must read for your issue. It looks like its now part of the ArcGIS 10 documentation but its the same basic document its been for several versions.
http://help.arcgis.com/en/sdk/10.0/arcobjects_net/conceptualhelp/index.html#//0001000000wm000000

They talk about how it takes a long time to dig into a Geometry Object using ArcObjects from .NET and compare it to the Visual C++ ArcObjects API which has no interop to deal with if I understand it correctly.

Here is the help link for the Visual C++ version of the ArcObjects API.
http://resources.esri.com/help/9.3/arcgisengine/com_cpp/vcpp_start.htm

I know this means learning a new API and new syntax but if performance is what you are looking for while trying to support different kinds of Feature Classes (everything from a Shapefile to an SDE Feature Class) then I think this is the way to go.