GiD forum

Hi, I have to generate a surface from a cloud of 10,000 data points. The
convex hull (x-y wise) of those points form an irregular shape. I have a
few questions:

1) The surface formed from the points is rectangular, I would like it
better if the surface did not extend beyond the initial given points
i.e. if it would fit exactly the convex hull of the points. How can it
be done?

2) I can see no mean of controlling the degree of approximation of the
surface nor verifying to which extent the surface is a good
approximation to the points. Is there a way to do that?

Thanks

Alexandre Forest
ETS, Montreal, Qc

Hi Alexandre,

I had the same problem as you.
This is what the GiD-Support wrote me:



"To create a surface from a cloud of points gid projects the points to a
plane;
so, if the cloud of points has a strange shape (a sphere, for example) it's
not
possible to create the surface.

The surface created is only an approximation to the selected points/lines,
not
an interpolation.

This function is useful in topography, to create reliefs and terrains.

http://gid.cimne.upc.es/support/gid_8.subst#SEC85
"


It is better to use a geometric modeller for this task. I am using now ACIS
from Spatial, but you can use also a free nurbs library like NURBS++, GUL,
...

The problem is the import to GiD. For the next version there will be a
revised ACIS SAT Import.

If you have a better idea in the meantime, please tell me, you know i have
the same problem!

Best Regards,

Alex



-----Original Message-----
From: gidlist-admin at gatxan.cimne.upc.es
[mailto:gidlist-admin at gatxan.cimne.upc.es]On Behalf Of Alexandre Forest
Sent: Monday, July 29, 2002 10:40 AM
To: gidlist at gatxan.cimne.upc.es
Subject: [GiDlist] NURBS surface from points (gid 7.1)


Hi, I have to generate a surface from a cloud of 10,000 data points. The
convex hull (x-y wise) of those points form an irregular shape. I have a
few questions:

1) The surface formed from the points is rectangular, I would like it
better if the surface did not extend beyond the initial given points
i.e. if it would fit exactly the convex hull of the points. How can it
be done?

2) I can see no mean of controlling the degree of approximation of the
surface nor verifying to which extent the surface is a good
approximation to the points. Is there a way to do that?

Thanks

Alexandre Forest
ETS, Montreal, Qc

_______________________________________________
GiDlist mailing list
GiDlist at gid.cimne.upc.es
http://gid.cimne.upc.es/mailman/listinfo/gidlist

Thanks fr the help!!

I finally generated my surface with the Rhino 2.0 modeler (evaluation
version). Just import the points (readcommandfile), draw manually the limits
for your surface (with polylines) and use the command patch to create and
adapt your surface.

I finally created a volume containing this "point cloud" surface and
exported it to GiD with the ACIS 4.0 format.

----- Original Message -----
From: "Alexander Muthler" muthler at bv.tum.de
To: gidlist at gatxan.cimne.upc.es
Sent: Tuesday, July 30, 2002 1:24 AM
Subject: RE: [GiDlist] NURBS surface from points (gid 7.1)


Hi Alexandre,

I had the same problem as you.
This is what the GiD-Support wrote me:



"To create a surface from a cloud of points gid projects the points to a
plane;
so, if the cloud of points has a strange shape (a sphere, for example)
it's
not
possible to create the surface.

The surface created is only an approximation to the selected points/lines,
not
an interpolation.

This function is useful in topography, to create reliefs and terrains.

http://gid.cimne.upc.es/support/gid_8.subst#SEC85
"


It is better to use a geometric modeller for this task. I am using now
ACIS
from Spatial, but you can use also a free nurbs library like NURBS++, GUL,
...

The problem is the import to GiD. For the next version there will be a
revised ACIS SAT Import.

If you have a better idea in the meantime, please tell me, you know i have
the same problem!

Best Regards,

Alex



-----Original Message-----
From: gidlist-admin at gatxan.cimne.upc.es
[mailto:gidlist-admin at gatxan.cimne.upc.es]On Behalf Of Alexandre Forest
Sent: Monday, July 29, 2002 10:40 AM
To: gidlist at gatxan.cimne.upc.es
Subject: [GiDlist] NURBS surface from points (gid 7.1)


Hi, I have to generate a surface from a cloud of 10,000 data points. The
convex hull (x-y wise) of those points form an irregular shape. I have a
few questions:

1) The surface formed from the points is rectangular, I would like it
better if the surface did not extend beyond the initial given points
i.e. if it would fit exactly the convex hull of the points. How can it
be done?

2) I can see no mean of controlling the degree of approximation of the
surface nor verifying to which extent the surface is a good
approximation to the points. Is there a way to do that?

Thanks

Alexandre Forest
ETS, Montreal, Qc

_______________________________________________
GiDlist mailing list
GiDlist at gid.cimne.upc.es
http://gid.cimne.upc.es/mailman/listinfo/gidlist

_______________________________________________
GiDlist mailing list
GiDlist at gid.cimne.upc.es
http://gid.cimne.upc.es/mailman/listinfo/gidlist