The USDA classifies soils into twelve types (called "textures"), based on their relative percentages of sand, silt, and clay; since these three percentages total 100, any soil sample can be plotted on a ternary graph: an equilateral triangle whose apexes represent pure sand, pure silt, and pure clay. I represent each texture by an instance of PolygonMorph; since a PolygonMorph can tell whether any specified point is within its boundry, I can classify any soil sample by asking each texture in turn "does this soil sample belong to you?"
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