In a highway Project, I have to design a road connecting to roads together. The map I have on AutoCAD is a elevation gridlines map and I have x, y and z coordinates but I don't know how to get an elevation for a point that is not exactly on a clear grid point, as the points where the grid lines intersect, the elevation is given.

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If you use ACad civil engineering, C3D, it automatically creates contour lines and surfaces from the grid data.

One way would be to draw circles from the point, P to the 4 grid points surrounding it and measure their radius, say r1,r2...

then a good estimate is $ Z_P= \frac{Z1r1+Z2r2+Z3r3+Z4r4}{r1+r2+r3+r4} $


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