UNDERSTANDING GEOMETRY.

There's any place were i can found info about the differents kind of Geometry that RH and GH Manage and the way to manipulated.

Cuz i'm having a headache trying to transform a polysurface FORM made with a few opperations EXTRUDE, TRIM ETC.

Into a proper Mesh to export it to ECOTECT through GECO.

Replies to This Discussion

Permalink Reply by David Rutten on March 12, 2014 at 3:57am

You can plug a Brep into a Mesh parameter and you'll get a mesh. If you want control over the mesh accuracy, then you'll need to use the [Mesh Brep] component, which accepts meshing settings as an input.

David Rutten

david@mcneel.com

Permalink Reply by Toussaint Jimenez Rojas on March 12, 2014 at 7:51am

David, i did what you said, but i don't understand well how to control the Mesh to achieve a Clean Mesh Construction as triangles or quads that will be suitable for further manipulation into GECO

with mesh surface the H value when i set it to true the MESH its smaller than the original surface i dont know why.

Attachments:

BUILDING ALONE.3dm, 3.6 MB
MESH-TROUBLE.gh, 9 KB

Permalink Reply by David Rutten on March 12, 2014 at 7:57am

That is not [Mesh Brep], that is [Mesh Surface]. If you want to take trims and joined surfaces into account you have to use [Mesh Brep]. It works just like the Rhino mesher.

[Mesh Surface] was made to create UV panels that can be equalized as much as possible to reduce the stretching effects underlying surface parameterization might have.

David Rutten

david@mcneel.com

Permalink Reply by Toussaint Jimenez Rojas on March 12, 2014 at 12:35pm

The second model is with Mesh Brep, but have a few mesh faces triangulated, there's any way of clean that to build a clean mesh or in effect force the triangulation to be regular ?

thats why im asking to technical info about meshed to really understand how they works inside RH and GH and how to manipulate it, its a little bit difficul to follow a lot of spare info all over the web and the forum.

Permalink Reply by David Rutten on March 12, 2014 at 1:14pm

Ok, I'm no expert on meshing in general and Rhino's mesher in particular, but here's roughly what I know, in no particular order:

Grasshopper provides 3 built in methods for meshing surfaces and breps: [Mesh Brep] which used the Rhino mesher, [Mesh Surface] which create a rectangular grid of mesh faces on a single surface and [Simple Mesh] which attempts to represent each face in a Brep using a single Tri or Quad and accuracy be damned. Let's focus on the easy ones first...
[Simple Mesh] is a first attempt at providing a completely reductionist meshing engine. It was born out of a skype discussion I had with Brian James one night during the weekly Seattle RMA developer meeting. It only handles very simple cases at the moment so it's probably not all that useful, but it's there anyway just in case. If this mesher cannot handle a certain Brep face because it's too complicated it will use the native Rhino mesher for that face.
The purpose of [Mesh Surface] is to provide a single surface mesh that isn't distorted by the underlying parameterization of a surface. My approach for this actually turned out to be really slow, which is why the [Q] input is set to false by default. This mesher was never designed to take trims into account, however you get a single option [H] to control how trims interact with the mesh.
[Mesh Brep] merely channels the native Rhino mesher. You can supply meshing settings that look a little bit like the meshing settings that Rhino itself exposes. With these settings you can control how seams in breps are handled, how much the mesh is allowed to deviate from the underlying geometry, how many quads you want etc. This is the most customizable option, but even here it's totally possible you can't get what you want. For example, there is no way to enforce a mesh that contains only quads. As soon as seams are stitched or whenever trims are present, you're going to get triangles along the edges of meshes.

David Rutten

david@mcneel.com

Permalink Reply by Toussaint Jimenez Rojas on March 12, 2014 at 1:26pm

David Thank you a lot for your response now i have a clear starting point about meshes inside GH to start to handle it i want you to congratulate you cuz you always try to found a diligent answer in the best way possible about issues, troubles, and curious things among all the users registered in the Forum.

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