71 lines
1.9 KiB
Lua
71 lines
1.9 KiB
Lua
local M = {}
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-- Source with pseudocode: https://de.wikipedia.org/wiki/Punkt-in-Polygon-Test_nach_Jordan
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-- see also https://en.wikipedia.org/wiki/Point_in_polygon
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-- parameters: points A = (x_a,y_a), B = (x_b,y_b), C = (x_c,y_c)
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-- return value: −1 if the ray from A to the right bisects the edge [BC] (the lower vortex of [BC]
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-- is not seen as part of [BC]);
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-- 0 if A is on [BC];
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-- +1 else
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function M.cross_prod_test(x_a,y_a,x_b,y_b,x_c,y_c)
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if y_a == y_b and y_b == y_c then
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if (x_b <= x_a and x_a <= x_c) or (x_c <= x_a and x_a <= x_b) then
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return 0
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end
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return 1
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end
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if not ((y_a == y_b) and (x_a == x_b)) then
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if y_b > y_c then
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-- swap b and c
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local h = x_b
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x_b = x_c
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x_c = h
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h = y_b
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y_b = y_c
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y_c = h
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end
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if (y_a <= y_b) or (y_a > y_c) then
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return 1
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end
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local delta = (x_b-x_a) * (y_c-y_a) - (y_b-y_a) * (x_c-x_a)
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if delta > 0 then
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return 1
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end
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if delta < 0 then
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return -1
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end
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end
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return 0
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end
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-- Source with pseudocode: https://de.wikipedia.org/wiki/Punkt-in-Polygon-Test_nach_Jordan
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-- see also: https://en.wikipedia.org/wiki/Point_in_polygon
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-- let P be a 2D Polygon and Q a 2D Point
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-- return value: +1 if Q within P;
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-- −1 if Q outside of P;
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-- 0 if Q on an edge of P
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function M.point_in_polygon(poly, point)
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local t = -1
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for i=1,#poly-1 do
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t = t * M.cross_prod_test(point.lon,point.lat,poly[i].lon,poly[i].lat,poly[i+1].lon,poly[i+1].lat)
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if t == 0 then break end
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end
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return t
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end
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-- Convert rectangular defined by two point into polygon
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function M.two_point_rec_to_poly(rec)
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local poly = {};
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poly[1]["lon"] = rec[1].lon
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poly[1]["lat"] = rec[1].lat
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poly[2]["lon"] = rec[2].lon
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poly[2]["lat"] = rec[1].lat
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poly[3]["lon"] = rec[2].lon
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poly[3]["lat"] = rec[2].lat
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poly[4]["lon"] = rec[1].lon
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poly[4]["lat"] = rec[2].lat
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return poly
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end
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return M
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