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.