Test points for Brep inclusion fails

Replies to This Discussion

Permalink Reply by Stencil on January 21, 2010 at 10:10am

I still can't figure out what the problem is, though it seems so simple. Here's another screenshot of the whole definition.

What is the S-input on the Inside component? I can't find any information on the net, the Wiki or here about this component. I've played around with different settings, but without results.

Permalink Reply by David Rutten on January 21, 2010 at 10:21am

Is the point actually comfortably inside the box, or is it touching one of the box faces? Points are officially supposed to be coincident with surfaces tend to randomly fall towards the inside or the outside when evaluated. After all, the difference between 0.2e-68 and -0.2e-68 is very very small, much smaller than the accuracy you're working with. However, one of the numbers is positive (inside) and one of them is negative (outside).

--
David Rutten
david@mcneel.com
Poprad, Slovakia

Permalink Reply by Stencil on January 21, 2010 at 11:32am

Hi David, thanks for having a look.

I've tried placing the point in the middle of the box, but that doesn't change anything. The point is definately inside the box, but the Inside component doesn't identify it as a point on the inside.

Permalink Reply by David Rutten on January 21, 2010 at 12:02pm

Ok, sorry, I see now what's wrong.

The problem is this; you have a grid of points (many points) and you have two boxes. When you operate on these structures with the Inside component, it will match them up in the following way:

first point | first box
second point | second box
third point | second box
fourth point | second box
.....................................
hundreth point | second box


You need to compare ALL points with ALL boxes, then combine the inside/outside results until you eventually go back to a single boolean value. If you have a limited (fixed) number of boxes, say two or three, you can duplicate the operation and then combine the result:

If however you need to cater for a flexible number of boxes, it becomes a lot more complex. You need to have a good grasp of data layout and data matching if you want to make sure that the points and boxes are matched up correctly:

--
David Rutten
david@mcneel.com
Poprad, Slovakia

Permalink Reply by Juan_P on May 21, 2010 at 10:22am

Hello David,

I found this discussion very interesting, so i went on to try your screen shot (top)..
for some reason, the definition isnt working, I think this is the problem...
both "Inside" components are spitting back "false" statements. therefore feeding the "false" into the Gate Or component...making the output of the Cull Pattern component say.. "empty generic data list.. how can i fix this??

thank you
Juan_P

Permalink Reply by to] on January 21, 2010 at 12:03pm

Hi stencil

first of all just for visual information turn on the fency wires (you find it in the fly out view) then the transmitted information is easier to read for you and us ;)
tested your file and you are right the brep inclusion is not testing every brep it only gives you the points for the last connected object

see attached image if you need a fast workaround until it is fixed
(you have to flatten the tree for the pointgrid both for inclusion test and dispatch)

Permalink Reply by Gustavo Reis on May 16, 2018 at 7:41am

Hi David, I have been playing aroung with the Point in Brep component and some points that are actually outside of a closed Brep are been shown as if they were inside of it. Is it related to the tolerance you mentioned or am I doing something wrong with my definition? Thanks a lot!

Attachments:

• PointInBrep_tolerance.gh, 14 KB

Permalink Reply by Stencil on January 21, 2010 at 2:00pm

Thanks David and to], I'm still pretty new at GH so I appreciate your help!

Problem solved for now, but what kind of component is the one with the blue arrow in Davids definition?

Permalink Reply by to] on January 21, 2010 at 2:05pm

it is called pathmapper : logic/path mapper(red cube)
with that component you can work on the data layout (pathlogic...very important for working with grasshopper...thats why i recommended you to turn on fency wires)

Permalink Reply by Stencil on January 21, 2010 at 2:21pm

Oh! Path mapper has an extensive Help-file - I'll check it out immediately. Thanks!