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Re: Understanding IDLanROI [message #72990 is a reply to message #72853]

Wed, 20 October 2010 10:01

guillermo.castilla.ca is currently offline

guillermo.castilla.ca
Messages: 27
Registered: September 2008

Junior Member

kBob writes:
> I am attempting to use IDLanROI to determine if Shapefiles overlap
> another Shapefile...
> When I tried to use the US shapefile in IDLanROI (and IDLgrROI) there
> was a line running across the United States from the Northeast to
> Hawaii.

I think what happened is that when you created those ROI objects, you
provided the entire set of vertices that define the shape of the US as
a single part, and then the last vertex of the ring defining the
conterminous US got connected with the 1st vertex in Hawaii, hence the
line you mention. I think the IDLanROIGroup::ContainsPoints method
should work properly if you create the corresponding object by adding
sequentially the parts in the US shapefile entity, providing neither
of the parts are holes (e.g., imagine that Colorado had successfully
opted out of the Union; the ring defining its shape would be a hole,
and its vertices would be listed counterclockwise in the shapefile
entity). Since afaik there are no holes in the US territory, the above
method should work without having to resort to the tessellator or
other graphic object classes.

But in a more general application (i.e., where there are polygons with
holes), I wonder what would be the way to find out whether a point is
inside a polygon that contain holes. The IDLanROIGroup cannot be used
for that, as there is no way to specify that a given ROI within the
groups is actually a hole. The easiest solution would be that the
ITTVIS folks implement the IDLffShape::ContainsPoints method. Now that
there is a larger interest to integrate image analysis with vector
GIS, there is some hope that this will happen in a future release...

Guillermo

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[Message index]

		Understanding IDLanROI By: KRDean on Fri, 08 October 2010 14:13
		Re: Understanding IDLanROI By: KRDean on Tue, 19 October 2010 08:02
		Re: Understanding IDLanROI By: David Fanning on Tue, 19 October 2010 10:38
		Re: Understanding IDLanROI By: guillermo.castilla.ca on Wed, 20 October 2010 10:01
		Re: Understanding IDLanROI By: KRDean on Fri, 22 October 2010 07:16
		Re: Understanding IDLanROI By: Matt[2] on Mon, 25 October 2010 09:17
		Re: Understanding IDLanROI By: guillermo.castilla.ca on Wed, 27 October 2010 08:44
		Re: Understanding IDLanROI By: guillermo.castilla.ca on Mon, 01 November 2010 06:23
		Re: Understanding IDLanROI By: guillermo.castilla.ca on Mon, 01 November 2010 06:24
		Re: Understanding IDLanROI By: David Fanning on Tue, 19 October 2010 14:02
		Re: Understanding IDLanROI By: KRDean on Tue, 19 October 2010 13:19

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