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Author Topic: What is the meaning of "indexed polygon"?  (Read 2212 times)
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« on: October 25, 2007, 07:20:25 am »

    Hi,I am very new in CS.
    In the user manual of Polygons( in chapter 4.6.1 geometry library), it mentions that "The most important type for the engine is the indexed polygon, which does not store its vertices as 3D vectors but only as indices in a table." I can't understand the sentence.    And it also mentions that " First, there are the basic 2D and 3D polygons that store their vertices as 3D vectors. The clippers are similar to this but they are specialized on clipping other polygons (you lay the clipper somewhere on a polygon and cut everything away of the polygon that is outside the clipper, resulting in a new, smaller polygon. Then there is a 2D polygon that stores its sides as line segments, not its vertices as vectors", why after using clippers, we store its sides as line segments, not its vertices as vectors?
     Thank you very much for your help!
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jorrit
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« Reply #1 on: October 25, 2007, 07:24:18 am »

Quote from:  link=topic=1452.msg6617#msg6617 date=1193293225
    Hi,I am very new in CS.
    In the user manual of Polygons( in chapter 4.6.1 geometry library), it mentions that "The most important type for the engine is the indexed polygon, which does not store its vertices as 3D vectors but only as indices in a table." I can't understand the sentence.    And it also mentions that " First, there are the basic 2D and 3D polygons that store their vertices as 3D vectors. The clippers are similar to this but they are specialized on clipping other polygons (you lay the clipper somewhere on a polygon and cut everything away of the polygon that is outside the clipper, resulting in a new, smaller polygon. Then there is a 2D polygon that stores its sides as line segments, not its vertices as vectors", why after using clippers, we store its sides as line segments, not its vertices as vectors?
     Thank you very much for your help!

Well an indexed polygon is just a number of numbers (indices). For example, an indexed polygon could be 3, 4, 8, 12. This means that it is a polygon made out of the vertices with index 3, 4, 8, and 12. To get the position of each vertex you would then use that index in a table of vertices that is kept separatelly from the polygon.

You misunderstood the line segment statement. Between. 'resulting in a new, smaller polygon' and 'Then there is a 2D polygon ...' it is a different sentence. The clipper returns normal polygons with normal vertices. The line segment sentence is not related to that clipper at all.

Greetings,
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