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60 lines
2.9 KiB
60 lines
2.9 KiB
6 years ago
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===============================================================================
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Project: Shape_PoinInPoly
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Purpose: Sample and the function for calculatin a point in a polygon
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(complex,compound - it doesn't matter). Can be used for labeling.
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Author: Copyright (c) 2004, Marko Podgorsek, d-mon@siol.net
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===============================================================================
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Requires: shapelib 1.2 (http://shapelib.maptools.org/)
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Tested and created on platform:
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Windows 2000 Professional
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Visual Studio .NET 7.0
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P4 2.4 GHz
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1GB RAM
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I just found out about the ShapeLib, GDAL and OGR and I must say that they're
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all great projects.
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I belive I'll use some of those libraries in the future. Right now I'm using
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only shapelib.
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The thing that led me to the http://wwww.maptools.org was the need of finding
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the point in poly...but as I found out that even OGR didn't support it. So
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there I was. I was forced to make my own function. Well, it was fun. I learned
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a lot.
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I wrote this function for the Autodesk Autocad 2004 MPolygon, because there was
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no function to do this in the Object Arx SDK (the Acad programming SDK). Well,
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it will be in the 2005 release...but, still. There is a function in the
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Autodesk Map 2004 version...in the menu.
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Not useful when you need the coordinates, not the point on the screen...
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So when the Acad version was done I was thinking of doing it on the Shape files,
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too. A little bit of changing the structures and variable
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types (so they're not using Object Arx) and I was done.
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And here it is....Contribution from me to the ShapeLib world :)...and maybe even
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OGR (a little bit of changing there).
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Some statistics:
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For about 69000 polygons in Autocad picture (.dwg files)
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Autodesk Map 2004 was creating centroids (the menu command) about 45s (1 scan
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line)
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My function, with 3 scan lines took about 5s. And I was drawing the dots on the
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picture...
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-------------------------------------------------------------------------------
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DPoint2d CreatePointInPoly(SHPObject *psShape, int quality)
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The second parameter quality tell the function just how many rays shall it use
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to get the point.
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quality = 3 works very well, but anything below 5 is good.
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This doesn't mean that the execution will slow down, but it just finds a good
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point. That's all.
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The qality shows on the compound objects (multiple poligons with more than one
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exterior loop) - if not enough rays, then there may be no centroid.
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Or the U shaped thin polygon, only the bootom (below the y center line) is fat.
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Autodesk Map with one scan line will create the centroid on one of the thin
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parts, because it only uses the y center line. If you have more rays, one will
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surely pass the fat area and centroid will be created there.
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-------------------------------------------------------------------------------
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Anyone using this function:
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Just send me an e-mail, so I'll see if I did anything good for the public.
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And you can send me e-mail with questions also.
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