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Point in Polygon
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02-12-2006 18:31

Posted by:

San Francisco, CA

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Does TNT Basic have a point in polygon feature?
If not, how would I do this?

And how do I test if an oval or circle is touching a polygon?

And one more thing, how about testing if a polygon is touching another polygon?

02-12-2006 23:36

Posted by:

hertfordshire (England)

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There is 'In Map Polygon'...

...but if you are talking about a general polygon, drawn to a screen, then no TNT doesn't support a test of this type.

How to implement it? It's a relatively simple algorithm to explain, but a bum to implement. Your best bet is to post this as a feature request, it would fit nicely with your request for loading polys from an array. There is a call in the underlying QT API that would solve the problem, and this could be implemented fairly easily. If you want this sort of call now then it can be done but you are talking about scan conversion algorithms, and it's a lot of math...

An Oval touching a poly? Forget it... Again it can be done, but it's a far too specific thing to be worrying about, and this is SERIOUS math!

Two overlapping polys? There is an underlying call which tells you if two regions overlap, anything more than that and you are back to the above question. If you are looking for points of intersection then it is really not going to happen, at least for a long time.

If you would like to know how to do the point in poly test then drop me a line and I'll mail over some theory, I've done this sort of thing before (in C) and it's not pretty.

Danny (nods)

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