Hi Andrada,
There are two ways which come to my mind for that right now, perhaps there are more.
The first one takes the topographical “plane” and with an Extrude, while “Create Caps” is enable, the first step can be done. Extrude here only a tiny little bit down, just so you can see the thickness of the object. While the new polygons are selected, use the Y-axis and move the new polygons much more down, enough for the targeted cube volume. Then call up a cube and increase the amount of segment, and Boole it with the “A intersect B” setting.
The second method follows the idea to place a Spline guide over the landscape mesh. This needs to be placed in the top view. Four straight lines creating a square, but the lines have longer ends, so the edges outside the square will be guided/cut as well. It helps to use the knife tool with “snapping” on points. Four cuts and then select you can select that new defined square.
The Extrude part works as above, just a tiny little bit down, really tiny, nearly invisible!, and then drag it way down. Keep the selection and got go to Coordinate Manager (not the one in the Attribute Manager) and set the Y.size to zero—this will flatten the “floor” of your landscape cube.
It might be very helpful, if the new cube is rotated on the landscape, to first rotated the landscape, so the resulting square is parallel to the top-view sides. Selections are much faster than. To rotate the view might be an alternative.
You might “Break Phong Shading” for the resulting edges along the “topo/cube” or try to introduce some more edges…
In both cases, check the Normal direction and fix it, so all polygons have teh same direction.
All the best
Sassi
