Challenge #161: Triangles, Triangles, Triangles

[TonyA]

Here's my solution. Had a lot of fun playing with various sorts on the final data set, trying to figure out how to match the image (area, min X, min Y in ascending and descending order). Came up with some interesting patterns, especially the last two which are sorted on area in ascending and descending order. But I couldn't find the sort order that matched the image.

Also learned a few interesting things looking at the solution:

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I didn't realize you could do comparisons on polygons. I thought that Alteryx was comparing the underlying GeoJSON so the order of the points would matter. Apparently it's smarter than that, which makes the problem a lot simpler. Another thing that makes my workflow longer is that I tried to stick to what I thought was the spirit of the exercise and use spatial tools instead of formulas whenever possible.

[Martyn]

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[rougeau14]

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My associate @CharlieS came up with this one!

[bnelly1987]

[hanykowska]

Definitely not an optimal solution, but, hey, it works!

Spoiler

[garthn555]

The extra 21 objects (537-516) seem to be true triangles - the nulls are lines. (I added collinear test records to check). So does that mean if 3 collinear points are used in st_createpolygon that it won't produce a spatial object?

[CharlieS]

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@garthn555 wrote:

The extra 21 objects (537-516) seem to be true triangles - the nulls are lines. (I added collinear test records to check). So does that mean if 3 collinear points are used in st_createpolygon that it won't produce a spatial object?

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Yes, 3 perfectly collinear spatial points will yield "ST_CreatePolygon: Failed to form valid polygon."

That being said, the issue with this scenario is introduced by the Make Grid tool and the issues of plotting a flat plane to a curved surface. The grid points are not technically collinear, but practically they are, and therein lies the issue. 

[ddiesel]

I was stuck for the longest time at 540 triangles before I peeked at the solution to see that the area tolerance was set to > .1 sq miles.

My solution:

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