Say that I have a mesh and a curve. Then I can shrink-wrap the curve so it follows the mesh. Is it possible to flatten the mesh in the perpendicular direction to the curve to make space for a road along the curve.
Original cross-section:
New cross-section:
The road is supposed to go on the shelf.
Notice that this is a cross-section. The cross-section has a flat segment, but it may still have a gradient into the screen plane. This "Bulldozer" may use surface average, surface min, or surface max, computed along each cross-section the road passes, as reference for where to build the road.
In mathematical terms:
Let the initial elevation be z(x, y), and assume that z is differentiable. Then its gradient is
$$ \nabla z = \frac{\partial z}{\partial x}\hat{\boldsymbol{x}} + \frac{\partial z}{\partial y}\hat{\boldsymbol{y}} $$
Without loss of generality, assume that the road is going in the $x$ direction. With this choice of coordinates, the figures shows the $yz$-plane. After the modifier, I want
$$ \nabla z = \frac{\partial z}{\partial x}\hat{\boldsymbol{x}} $$
because there should be no slope orthogonal to the road. While the original solution fulfils this criterion (in fact, it sets $\nabla z = 0$ along the road), I do want to keep a non-zero $x$-derivative. You wouldn't push away an entire mountain to keep the road flat in all directions, would you?
Here is a picture: https://www.epikdrives.com/grossglockner-high-alpine-road, notice that the road keeps flat in one direction, but still has a non-zero derivative in the other direction. The "bulldozer" is required because any road as a non-zero thickness.
