GeomAPI_ProjectPointOnSurf gives wrong UV for a plane

Michael Li
Wed, 10/10/2018 - 02:21

Forums:

Hi,

I was trying to obtain the UV coordinate of the nearest point (in the sense of orthogonal projection) on a surface for a given point. I tried a simple case with a point near a plane using GeomAPI_ProjectPointOnSurf. The NearestPoint function gives the correct result, but the UV seems wrong (and so is the point computed by UV). The UV coordinates are obtained by calling LowerDistanceParameters.

I created a nominalistic example in the attachment that reproduces this error. The plane has x-axis (0,-1,0), y-axis (0,0,1), z-axis (-1, 0, 0), location (-63.5, 4.30893, 0). When I tried to project a point (-64.5, 2.88691, -3.00001) onto the plane, the UV I got is (1.42202, -66.5). The U coordinate looks correct, but V coordinate is clearly off by a far margin. The same issue appears when I tried ShapeAnalysis_Surface. Perhaps I'm misunderstanding something, but it feels the projection shouldn't fail in such a simple case.

Thanks,

Michael

Attachments:

test_0.cpp

Forum supervisor
Wed, 10/10/2018 - 10:47

Dear Michael,

We have performed the simple test with your data and didn't find any issue. You can see our test result below.

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Best Regards,

Forum supervisor

gp_Ax3 ax3(gp_Pnt(-63.5, 4.30893, 0), gp_Dir(-1, 4.35e-15, 0), gp_Dir(-4.35e-15, -1, 0));

Handle(Geom_Surface) surface = new Geom_Plane(gp_Pln(ax3));

gp_Pnt p(-64.5, 2.88691, -3.00001);

GeomAPI_ProjectPointOnSurf proj(p, surface, -100, 100, -100, 100, 1e-7);

double u, v;

proj.LowerDistanceParameters(u, v);

gp_Pnt p_surf = surface->Value(u, v);

gp_Pnt p_near = proj.NearestPoint();

printf("p:(%f, %f, %f),\np_near:(%f, %f, %f),\nuv: (%f, %f),\ndist: %f,\np_surf:(%f, %f, %f)\n", p.X(), p.Y(), p.Z(), p_near.X(), p_near.Y(), p_near.Z(), u, v, proj.LowerDistance(), p_surf.X(), p_surf.Y(), p_surf.Z());

Output:

p:(-64.500000, 2.886910, -3.000010),

p_near:(-63.500000, 2.886910, -3.000010),

uv: (1.422020, -3.000010),

dist: 1.000000,

p_surf:(-63.500000, 2.886910, -3.000010)

Michael Li
Wed, 10/10/2018 - 20:51

Thanks for the reply! Which OS are you running the test on? I tried this program on another Mac OS and the UV coordinate I got is still (1.42202, -66.5), which has the wrong V coordinate.

Forum supervisor
Thu, 10/11/2018 - 12:55

Dear Michael,

The next Draw script of OCCT 7.3.0 works properly on macOS 10.13 High Sierra

pload ALL

plane pl -63.5 4.30893 0 -1 4.35e-15 0 -4.35e-15 -1 0

proj pl -64.5 2.88691 -3.00001

#ext_1 Parameters: 1.4220200000000047 -3.0000100000000001

Best Regards,

Forum supervisor