hi！
I want by side edges to select primitive,like Slio ,Such as select all four sides face, or any sides face, how can i do?

Hi, there. Access to edge information is pretty limited except maybe through the HDK so I don't know of a way of selecting based on number of edges. However, if you are using polygons, you can achieve a similar result by selecting based on number of vertices. For example, in a Group SOP, Change it to “Group by Expression”, and use an expression like “$NVTX == 3” to select primitives with 3 vertices.

Oh! ophiuchus, that's marvelous! thanks！

ophiuchus42
Hi, there. Access to edge information is pretty limited except maybe through the HDK so I don't know of a way of selecting based on number of edges. However, if you are using polygons, you can achieve a similar result by selecting based on number of vertices. For example, in a Group SOP, Change it to “Group by Expression”, and use an expression like “$NVTX == 3” to select primitives with 3 vertices.

Why not work on the sphere？

Hey donghonzi is you sphere polygons? By default, spheres in Houdini are primitives

grayOlorin
Hey donghonzi is you sphere polygons? By default, spheres in Houdini are primitives

Of course I know，but use group “$NVTX == 3”，poly sphere of the triangles is not selected，I do not know why……

Could you post a screenshot of your parameter editor for the group node or your hip file? Your expression seems correct

:shock:

Ha ha, oops. I guess it doesn't always work. In this case it looks like all the polygons in the sphere are generated with four vertices, but for the primitives on the top and bottom, two of the vertices share the same point, so they have 4 vertices, and 3 edges. If you drop down a fuse SOP (use the default consolidate mode) after the sphere, the extra vertices are removed and it should work as advertised…

Thanks ophiuchus，but I do not fully understand，three point can have four vertex？

donghongzi
I do not fully understand，three point can have four vertex？

Picture a quad with one of the edges with 0 length, where two of points have the same position.

edward

donghongzi
I do not fully understand，three point can have four vertex？

Picture a quad with one of the edges with 0 length, where two of points have the same position.

thanks edward， yes..I get…but this way there are two points is not it? sphere only a single point，my point is sphere above and below the point of whether the four sides face?but they appear to be triangles，and ophiuchus42 said they have four vertices, triangles have four vertices it? Or that they are the four sides face?

Those “triangles” you see in the picture (ie. default Polygon Mesh Sphere) are not actually triangles. They are quads with a 0 length edge.

if you move point 0, you can clearly see that there is no other point there so the polygons should be triangles
but if you look at the spreadsheet, you can see that polygons are defined like quads using 2 times the same point
for example for face 0
vtx 0 is using point 0
vtx 1 is using point 0
vtx 2 is using point 3
vtx 3 is using point 2

so by number of vertices they can be called quads

so answer to your question is Yes, 3-point polygon can have 4 vertices

thanks tamte！I finally understand the！