# Re: Point Cloud Info Needed

From: Anshuman Razdan (razdan@taurus.eas.asu.edu)
Date: Tue Jan 13 1998 - 18:05:04 EET

This depends on how much data you want out of the file. The STL file itself
consists of triangles. SO it is an approximation of the original with plane
facets. If you were to use "center of the triangles" you essentially have 1/3
the number of data points. If you save the normal you can recreate the plane of
the triangle (not the triangle itself) since a point and normal is enough to
define a plane. Again depending on what you want to do with it - if you are
going to put it in a program to recreate the "free form surface" of the
original from the point cloud data, you are better of with all three vertices
(although STL file does not take care of redundancy i.e. if a vertex is shared
by 5 triangles that vertex is in the file 5 times), Any more points within the
triangle will be an overkill - three points are sufficient to define a
triangle.

Hoep this answers what your question !! If you describe the goal of your
project we will have better understanding and hopefully can give you better

On Jan 13, 9:50am, Delft Spline Systems wrote:
> Subject: Re: Point Cloud Info Needed
> >When creating a point cloud file from a STL file, are the points the center
of
> >the triangles or the three coordinates ?
> >
> >--
> >Thank you,
> >
> >Ingrid Timmel
> >Fisher Price
> >itimmel@fpp.com
> >
> >
>
> Basically you are of course absolutely free to create any type of point
> cloud file from your STL: it may even contain many points on the
> surface of each separate triangle to have a sufficiently dense point cloud.
>
> In case the density is no problem, than the best apporoximation
> of the original CAD model is given by the three vertices of every
> triangle (of course three coordinates per vertex). These points are
> on the original CAD-surface, while the flat triangle inbetween is just
> an approximation.
>
>
> Best Regards,
>
> Lex Lennings.
>
>
> ----------------------------------------------------------------------------
> ----------------------------
> Delft Spline Systems, The Netherlands.
> We offer DeskProto: affordable Rapid Prototyping using CNC milling
> mailto:info@spline.nl
> website:http://www.spline.nl
>
>-- End of excerpt from Delft Spline Systems

```--
Dr. Anshuman Razdan
Technical Director PRISM
***************************************************************
* Ph: (602) 965 5368 	FAX: (602) 965 2910
* Office: GWC 574       Email: razdan@asu.edu
* Snail Mail: PRISM, MCode 5106 Az St. Univ, Tempe AZ 852815106
* http://surdas.eas.asu.edu/~razdan
***************************************************************
```

This archive was generated by hypermail 2.1.2 : Tue Jun 05 2001 - 22:44:42 EEST