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[其他] API可以识别拓扑中的孤岛吗?

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ID    31245
Applies to:    AutoCAD Map 3

Date    12/10/2001

This document is part of   Visual Lisp   Autodesk MAP DevNotes   MAP Topology   Topology Lisp   


问题:Can API identify islands in topology?

I have a problem in managing the links of a polygon topology returned by the
LISP function, tpm_elemadj. Is there any way (without performing geometric
calculus) to understand if a specific link in the list is part of an island,
assuming there is one?

解答:
Answer
There is no function that does this exactly as AutoCAD Map does not specifically
identify islands within a topology. However, you could use the tpm_elemadj
function and the tpm_elemget function to trace the polygon elements. The link
ID's returned by tpm_elemadj are those actually adjacent to the indicated
element. So for example, there could be many links meeting at a given node. If
the argument to tpm_elemadj is a centroid ID, then all the relevant links are
returned.

Thus if you have links left over after your trace, you know they are part of an
island. In other words; if the total number of links you have traced, from link
to link, is less than the total number of links returned by tpm_elemget, then
the result is that you have at least one island.

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