Re: Octaviz help, general question about plotting scattered

[Jonathan Stickel]

Sorry to break the thread... replying to a digest.

Jordi

You can use the function griddata.m (geometry package of octave-forge, I 
think) to do what you want.  First define a regular grid, and then run 
griddata to interpolate your random points onto the grid.  For example,

> [X,Y]=meshgrid(xlo,xspan,xhi,ylo:yspan:yhi);
> Z = griddata(x,y,z,X,Y);
> vtk_surf(X,Y,Z)

where lower case x,y,z are your set of points.  Unfortunately, you will 
need to modify the griddata function at line ~52:

tri=delaunay(x,y,"QJ");

i.e. the "QJ" option must be used, or you will get segfaults since you 
are mapping to a regular grid.  (I tried to have this change checked in 
a couple years ago, and it was not accepted.  I don't know why!)


In your original post, you mention two other things.  About animations, 
I have found this mencoder command to work well for me (all one line):

$ mencoder mf://*.jpg -mf fps=20:type=jpg -ovc lavc -lavcopts 
vcodec=mpeg4:vbitrate=5000 -o output.avi

This can be used to animate a sequence of jpg files generated by 
octave/octaviz.  The frame rate can be set easily with the fps option. 
At some point, I figured out how to convert the mpeg encoding to 
something quicktime could use, but I don't remember how right now.


About colormaps in octaviz, you can set different colormaps using 
vtk_colormap.  The simplest usage is using pre-defined colormaps from 
octave-forge, e.g. jet.  But you can define your own colormap as a 3 
column matrix of r,g,b values.  I haven't done this myself, and so you 
may need to experiment a little bit to get what you want.

Nice to know others are using Octaviz!

Regards,
Jonathan




> Date: Tue, 17 Jul 2007 15:56:58 -0500
> From: " Jordi Guti?rrez Hermoso " <address@hidden>
> Subject: Re: Octaviz help, general question about plotting scattered
>         data
> To: octave-help <address@hidden>
> Message-ID:
>         <address@hidden>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> On 17/07/07, Carlo de Falco <address@hidden> wrote:
> > On 17/lug/07, at 03:33, Jordi Guti?rrez Hermoso wrote:
> >
> >
> > > My second question is no doubt more complex. Suppose I have scattered
> > > data points on some unstructured grid on the plane, and I have a
> > > function value at each point. That is, the only data I have is a bunch
> > > of (x,y,z) triplets that can be given to me in any order. They should
> > > represent samplings from a smooth function, hopefully a solution to a
> > > shallow water equation without shocks, once I get my code working. How
> > > can I form a quasi-smooth surface which interpolates with small
> > > polygons the data points that I give?
> > If I understand what you want to do,
> > you could use the function "delaunay" from the geometry package in  o-f
> > for creating a triangulation and then the functions in the package
> > FPL to plot the data.
>
> Thanks, I do think that's exactly what I want! Except that I really
> want to plot with Octaviz... I really need to dig into its VTK
> internals, I guess.
>
> - Jordi G. H.