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I have a polygon that represent a basin. The top of the basin is at 119 ft in elevation and the bottom of the basin is at 93 feet in elevation. I have created a TIN that represents this. I have segmented the polygon into multiple polygons, and I would like to find the surface area and volume of each of the polygons.

When I use Calculate Geometry to calculate the surface area of each of the polygons, I get values that seem reasonable. When I use the Polygon Volume tool to calculate the surface area/volumes of the polygons the numbers values do not match what was calculated with the Calculate Geometry tool. The values are off by ~200 ft. I cannot seem to figure out why the surface areas do not match up.

Attached is my attribute table for reference. The highlighted columns are the results of the Polygon Volume tool. The column named "SA_ft2" is the result of Calculate Geometry.

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Both the TIN and the polygon are projected in State Plane Texas South Central FIPS 4204 feet.

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    Polygon Volume calculates the surface area of the TIN that intersects the polygon layer, not the polygon boundary itself. Since a TIN is made up of triangles, it is not going to match the polygon boundaries perfectly. In this case, it calculates high, probably because there are numerous triangles that go beyond the polygon boundary, but the algorithm catches and calculates them because they touch the boundary. Just a guess. – Baltok Apr 29 at 21:08

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