Ah, now I get it. In the example, the angle is taken from the normal vector of the closest face on the mesh.
Basically a Cartesian movement is defined via a coordinate system, in Grasshopper referred to as a "Plane". In the Vector tab, there are multiple ways of defining a plane, such as via an origin point and two vectors (X, Y) or via an origin and a normal vector. Or you choose the "preset" orientations, like Plane XY, YZ, XZ.
Best,
Johannes
Basically a Cartesian movement is defined via a coordinate system, in Grasshopper referred to as a "Plane". In the Vector tab, there are multiple ways of defining a plane, such as via an origin point and two vectors (X, Y) or via an origin and a normal vector. Or you choose the "preset" orientations, like Plane XY, YZ, XZ.
Best,
Johannes