Choose point on a surface

Hello comunity.

This is very basic because I'm new in grasshopper.

I have a question: How can i choose a point of a geometry in grasshopper.

For example, i have a plane define by 4 points, an a want to choose the third point of that plane, how can i make this.

Thank you

Replies to This Discussion

Permalink Reply by David Rutten on October 23, 2014 at 4:25am

If the surface is untrimmed, you can evaluate it at either of the domain extremes {minU, minV}, {minU, maxV}, {maxU, maxV} and {maxU, minV} to get the four corners.

If the surface has an outer trim, you can convert the surface to a boundary curve, get the discontinuities in that boundary curve and enumerate those.

Without a picture it's difficult to know which solution would work for you.

Permalink Reply by Francisco Varela on October 23, 2014 at 4:45am

thank you for your fast reply.

i have a case and i want to make a pattern on the top surface of the geometry.

in my sense, i have to specify the plane of my box so that i can put a grid on that plane, yes?

after i have to create a pattern and say that pattern have to go to the specific plane taht i choose.

is this correct?

Attachments:

VHS.3dm, 323 KB
VHS.gh, 21 KB

Permalink Reply by David Rutten on October 23, 2014 at 5:18am

There are several ways to approach 'putting a grid on a surface'. The following is not an exhaustive list:

Use one of the Grid components to create the correct grid directly in the correct place+orientation.
Use one of the Grid component to create a grid at WorldXY, then map that grid onto the surface. This allows you to map a grid using a non-orthogonal mapping, for example if your target surface is stretched, tilted or even curved.
Divide the target surface into points or subsurfaces which are then used to construct a grid. This approach allows you to deal with trimmed surfaces as well as untrimmed ones.

As a side-note, I'd recommend against basing your logic on exploding bounding boxes. The order of vertices, edges, and faces is not guaranteed to be the same. It's better to directly access the boundingbox data in order to extract the required points, lines and planes (see attached).

I also attached a file that shows 2 ways of getting surface corners.

Attachments: