How to get the angles across a 3D surface?

I want to create a colorbar for the angle variations across an STL 3D surface. How can this be done effectively such as in the attached image?

Answer 1

[DGM]

I think this is what was meant.

unzip pringle_top.stl.zip % for the forum

% an STL file
T = stlread('pringle_top.stl');

% get the elevation angle for each face
fn = faceNormal(T);
th = acosd(fn(:,3)./vecnorm(fn,2,2));

% it's easier to set up scaled FVCData for a trisurf()
trisurf(T,'facevertexcdata',th);
axis equal; grid on; view(10,28)
xlabel('X'); ylabel('Y'); zlabel('Z')
colorbar

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