How to get UV from edge of planar

When I get the UV values on the plane, there are only max and min values. But I want to get all the values on the face, is this possible?

when I use BRepTools::UVBounds on the plane. Why is the UV value on the plane not 0 to 1, but a specific value?

How can I cut the trapezoid to get the plane normal vectors, and both are inside the plane(as shown in the picture)