# Meshing Technique question

New to Rhino.

Currently, the options available for a mesh generation are related to estimated number of quadrilaterals, mesh size, etc., but there is no control over the amount of nodes (or spacing) created along the boundary of a poly surface.

Say I have a surface defined by 4 boundary polylines (L1, L2, L3, L4). Is there a way I can subdivide each boundary line by a certain amount of segments and then generate a mesh that will be constructed in such a way to only connect to the boundaries by the segment nodes?.

For each perimeter line (yellow) that make up the polysurfaces, assign spaced tick marks (shown in black). These marks are forced locations where the mesh meets at adjacent plates. Then when the program generates the mesh, the program would create a mesh shown above (in red).

Can this be done in Rhino? Any guidance would be greatly appreciated. Thanks everyone.

Hi Robert - there is not… if surfaces are untrimmed, you can specify ‘minimum initial grid quads’ in the detailed controls and turn off (zero out) all the other controls to get a somewhat predictable grid, but not with any real control - you can’t tell the thing where to place the vertices.

-Pascal

Well, that’s unfortunate.

Is there a way to create those redlines manually? In particular, how do I select edges, subdivide them at discrete points, select two points on either side of the surface and have it draw a red line with curvature through the surface, adjust the generated red lines, and when I have all my redlines, do some command that will separate the redlines at intersections to create the mesh I want?

Hi Robert - it sounds like a job for a script or, more likely, Grasshopper.

-Pascal

Well, that’s unfortunate.

Is there a way to create those redlines manually? In particular, how do I select edges, subdivide them at discrete points, select two points on either side of the surface and have it draw a red line with curvature through the surface, adjust the generated red lines, and when I have all my redlines, do some command that will separate the redlines at intersections to create the mesh I want?

Quad Remesh is not working properly shown above. 2 quadrilateral polysurfaces… why does it not come out like this…

@Robert A few years ago I manual created a mesh terrain. Your case looks similar.

I didn’t mesh modelling like this in the last time and so I’m not sure what is possible at the moment. I think it’s a question which mesh tools can be used. Weaver Bird is a great tool and I would look at the Rhino 7 SubD section.
https://discourse.mcneel.com/c/serengeti/sub-d

Maybe something like this could be helpful? (Just an idea to develop)

Hi Robert,

You can rebuild NURBS surfaces and control the number of points in u- and v-direction. Set the u/v-degree to 1 then you can extract a mesh by the _ExtractControlPolygon command.
But you cannot control the spacing. In V7 there is a _Stitch command which helps to match the vertices along the seams. In V6 you could join the meshes and try the _AlignMeshVertices command.

Hi Everyone. Thank you for all your helpful ideas. I just saw this and I will try and tinker with your ideas. Thank you Mr. Golay for your help last Friday. Have a great week everyone. I will reply soon with an update on progress towards my solution…

Awesome! Thank you very much Helvetosaur!! Grasshopper is really cool!

This method will work but I need a workaround for this particular situation. The image above shows 3 surfaces adjacent to each other (ignore red line). If I use the UV meshing, the mesh lines will not match up correctly. I will have to split up the large surface into 2 smaller surfaces.

What is the best way in grasshopper to use this surface as input and to split this surface into two surfaces? The new point that defines the end of the red line can be the midpoint of the long edge as shown.

I’m going to tinker with Grasshopper some more and see if I can come up with something but any guidance would be very helpful. Thanks everyone!

Hi everyone. I learned the trim function so I got the answer to my previous question. One thing remains though.

I have two sliders hooked up to the UV mesh generator of this surface object. It is currently set to U = 9, V = 3 but this shape is only displaying 4 of the 9 in the U direction and is not conforming to the edge of the plate as shown. Most of my plates are behaving nicely but not this one. Files are attached. Does anyone have insight as to why this particular plate is misbehaving? Do I have to adjust it first in Rhino? Any guidance would be appreciated.

Happy Thanksgiving everyone!

Mesher - Practice Plate.3dm (488.3 KB)

Mesher- Practice Plate.gh (7.6 KB)

Found it. It is misbehaving because it is not a “surface”. It is a “trimmed surface”.

Command: ShrinkTrimmedSrfToEdge

Thanks everyone for your guidance and support. Have a great Thanksgiving everyone!