You have triangles. Each triangle determines a plane in three space. Find the intersection of that plane with a horizontal (constant height) plane, this will be a line. The direction of that line is the angle you seek.

Hm. If that is true; and I can't honestly dismiss it on first (nor second) reading, it is a brilliant observation and would save huge amounts of work. I would only need to consider those triangle that border the boundaries I'm interested in.

What's puzzling me is that I wasn't aware that I had described the angles I'm seeking in sufficient detail for anyone else to understand; but despite that, you've hit the nail on the head and saved me a huge amount of processing in the bargain.

Any pair of points of equal height, on any two of the three sides will define the angle of all pairs of equal height points across the triangle. so if I follow my boundary polylines, I only need consider those triangles on either side of them, and finding the angles is simple geometry.

I simply do not know how to thank you enough.

(And there are people who want to ban Anonymonk....)

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority". I knew I was on the right track :)
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re^2: Contour mapping? (Thank Dog for anonymonk.) by BrowserUk
in thread Contour mapping? by BrowserUk

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