Re^2: Contour mapping? (Thank Dog for anonymonk.)

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.

Comment on Re^2: Contour mapping? (Thank Dog for anonymonk.)

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Re^3: Contour mapping? (Thank Dog for anonymonk.) by Anonymous Monk on Apr 28, 2016 at 22:00 UTC
Thank me by not banning Anonymous Monk. Seriously, thanks for the feedback. I do all these short clear solutions, like Re^2: Comparing Lines within a Word List, Re: Comparing Lines within a Word List, and Re^2: Perl program to generate a descending order of 9-unique digit numbers, and nobody says a peep. BTW, the vector for constant height comes from `(P1 - P0) crossproduct (P2 - P0) crossproduct (0, 0, 1) Where P0 P1 P2 are points of the triangle, and (0, 0, 1) is the vertical vector` [download]	[reply] [d/l]
Re^4: Contour mapping? (Thank Dog for anonymonk.) by Anonymous Monk on Apr 28, 2016 at 23:09 UTC
Another BTW. Take that first crossproduct. It gives you a vector normal to the plane of the triangle. Cross it with a northern (y axis) vector and normalize the result. Then draw that triangle using a color proportional to the x component. Do for all triangles and you should get a pretty sun shaded picture of your data.	[reply]
Re^5: Contour mapping? (Thank Dog for anonymonk.) by BrowserUk (Patriarch) on Apr 28, 2016 at 23:30 UTC
One interesting, but awkward possibility -- that may never occur, but has to be dealt with in case it does -- is if all three points of a triangle are equal. Then the plane is flat and 'my angle' could cross it with any orientation. I'd have to look to the triangles adjoining the other two sides of the triangles that adjoin at my boundary to see how the potential flows through this boundary segment. Does your vector math cater to that? Thinking about it more, if a triangle is flat, then it is either a local peak or trough and the potential will flow around, but not through it. And that leads to the fact that if any segment on my boundary is formed by a pairs of points with equal height, then the potential will not cross the boundary through that segment at all, but rather will flow through the adjoining triangles, parallel to it; or not at all in the flat triangle case. 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.	[reply]
Re^6: Contour mapping? (Thank Dog for anonymonk.) by pryrt (Abbot) on May 02, 2016 at 23:57 UTC
Re^7: Contour mapping? (Thank Dog for anonymonk.) by BrowserUk (Patriarch) on May 03, 2016 at 04:05 UTC
Re^6: Contour mapping? (Thank Dog for anonymonk.) by Anonymous Monk on Apr 28, 2016 at 23:39 UTC
Re^7: Contour mapping? (Thank Dog for anonymonk.) by BrowserUk (Patriarch) on Apr 28, 2016 at 23:48 UTC
Some notes below your chosen depth have not been shown here
Re^4: Contour mapping? (Thank Dog for anonymonk.) by Anonymous Monk on Apr 28, 2016 at 22:41 UTC
all these short clear solutions... and nobody says a peep #JeSuisAnonymousMonk	[reply]
Re^3: Contour mapping? (Thank Dog for anonymonk.) by Anonymous Monk on Apr 29, 2016 at 00:54 UTC
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 You wanted angles, I gave you angles :)	[reply]