# Thread: How to draw the boundary(or maximum outline) of a point set?

1. Registered forum members do not see this ad.

I can 'connect the dots' in the 2nd picture of the OP with several more complex concave hulls...

2. Yes BIGAL, but you must remove additional triangles and then recreate boundary and that's all fine if points are random... Triangulation works well only if TIN (Triangular Irregular Network), and OP's picture is grid like... For that I suppose he/she could use routine for orthogonal connections... I remember I did exactly that here on cadtutor, only difference was that instead of points there were circles... And for boundary creation from 3dFACES I also did routine (not shrinkwrap from Civil) on autodesk/customization forum for OP Carlos Gil from Venezuela - only thing was the output was 3dpolyline...

3. That with circles was actually dimensioning - not boundary, but you can use my code with some mods. for boundary creation...

For 3dpoly around 3dfaces (after modified triangulation), try something like this... (not shrinkwrap from Civil)
https://forums.autodesk.com/t5/visua...t/true#M365245

HTH., M.R.

4. Originally Posted by marko_ribar
As far as I can tell, correctly implemented triangulation to random set of points should return convex hull boundary - not concave...
I think you are right,If these points are equidistant，The problem is easy to solve，And the random point sets seem to have many situations

5. Originally Posted by BIGAL
You are correct Marko the issue is to do with what we call long triangles have a look at this image, left is as built right is after edits and has the correct boundary.

Looking now 3 mistakes ? Need to fix and redo, these were little tiny slivers so the correct answer is both concave and convex, then LINEWORKSHRINKWRAP. We use delete long triangles via a length factor reducing till we start erasing ones we need then it becomes maual edits. I have been told we may have a 3rd party solution from our surveyors.

left after create triangles, middle is correct answer, right is convexhull.lsp
it is a good solution For equidistant point sets or approximate equidistant point set

6. Registered forum members do not see this ad.

It's for grid set of points with different dx and dy spacings...

Regards, M.R.