2D AND 3D Software problem

[irving2008]

Bill,

Thanks for that. There are lots of STL tookits available, not all are freeware. I have one for C# as that is my preferred programming language (VTK is for C++). There is also an import for HPGL, but thats a plotter output not the solid model for the building plots so only gives lines not the polygons - another format would be better.

[edit]A little explanation as to why the problem isnt as straightforward as it may seem: STL files model the suface by using triangles, therefore there are 3 X,Y,Z tuples for each triangle. Knowing the X,Y of a point on the building plot doesnt help unless it happens to coincide exactly with a X,Y of a vertex on a triangle... and in the building plot data we only have the ends of the lines - 2 X,Y tuples. So the problem is one of how do we decide if a given line on a building plot intersects with a given triangle in the landscape.... [/edit]

Reading the STL and HPG files is easy, its calculating the intersections thats tricky - not technically hard to do, but when you have, as in Ed's case maybe 50000 triangles in the landscape and 100 or so building plot polygons that could be around 5 million intersects to be checked. A polygon to polygon intersect requires around 20 or so floating point calculations to get to the decision whether there is an intersect or not so we are looking at something like 100m calculations, maybe several minutes processing on a 'normal' PC, assuming it can all fit in memory at once (not a problem on a reasonable spec PC).

Still thats quicker than doing it by hand eh?