Generate points on 3d section with vectors

Replies to This Discussion

Permalink Reply by Danny Boyes on May 21, 2012 at 7:50am

Do you mean something like this:

There is a Spreadsheet writer in gHowl which you will have to install separately to GH

Attachments:

• Sectioning.gh, 6 KB

Permalink Reply by Sam Gitelman on May 21, 2012 at 11:08am

Thank you Danny,

The only thing missing is vectors. It should look like 

{.3456, -1.0235, .5698, .71, .71, 0}

Permalink Reply by Danny Boyes on May 21, 2012 at 11:12am

Forgive my ignorance, but from where to where?

what are the components in {a, b, c, d, e, f} 

Permalink Reply by Sam Gitelman on May 21, 2012 at 11:22am

Each point has X,Y,Z coordinates. If you create a line through a point normal to the surface with length of 1 the projection of this line to the coordinate planes will give you the vectors.

Below is what I just found in Rhino help.

u- and v-directions

Every surface is roughly rectangular. Surfaces have three directions, u, v, and normal. You can display the u- and v-directions and the normal direction with the Dir command.

The u- and v-directions are like the weave of cloth or screen. The u-direction is indicated by the red arrow, and the v-direction is indicated by the green arrow. The normal direction is indicated by the white arrow. You can think of u-, v-, and normal-directions as corresponding to the x, y, and z of the surface.

These directions are used when mapping textures and inserting knots . 

 

Permalink Reply by Danny Boyes on May 21, 2012 at 2:57pm

I'm with you now. These are referred to as Frames in GH. A Vector is only direction and magnitude there is no location.

You need to evaluate a surface at a given UV to get these Frames but before you can do that you need to know the 2D co-ordinate on the Surface (U,V) of the given 3D point (X,Y,Z) for which you need the Closest Point on a Surface Component.

Attachments:

• Sectioning_Frames.gh, 7 KB