[GRASS-dev] wxNviz volumes

[Helena Mitasova]

On Jul 1, 2011, at 11:59 PM, Hamish wrote:

> Helena wrote:
>> It is crossections - we called them slices because you are
>> "slicing" through the volume 
>> but I guess that cross-sections is a more appropriate term
>> - I have a few examples here:
>> http://skagit.meas.ncsu.edu/~helena/publwork/MitSTCfigs2.ppt
>> It is pretty important part of volume visualization.
> 
> 
> Hi,
> 
> slightly off-topic, but something I've been wondering about-
> 
> do you have any good strategies for semi-automatically choosing
> isosurface levels? or do you just pick them by eye?
> 
> for isosurfaces and volume in general you really need to display them interactively
> so that you can see them from all sides and switch isosurfaces on and off
> basedon which level you are interested in and slice thruogh the volume.
> 
> For presentations, we have been using animations like these
> browsing through isosurface levels:
> http://skagit.meas.ncsu.edu/~helena/measwork/nc_coast/NHiso.gif
> http://skagit.meas.ncsu.edu/~helena/measwork/nc_coast/oi_iso.gif
> http://skagit.meas.ncsu.edu/~helena/measwork/nc_coast/oi_isoS.gif
> (I use gifs here because they are so easy to generate, but movie formats
> such as quicktime or mpg that have viewer that allows you to browse through
> the frames and stop where you want to show something interesting is better),
> decorations such as legend with pointer will also help

> If movie is not an option, for one of our publications,
> I included a set of images - each isosurface value in a separate image:
> http://skagit.meas.ncsu.edu/~helena/publwork/jcrbhi/JCRfig6_isosurfacesF.tif
> 
> These are some older volume movies by Bill Brown
> (they play little too fast on todays machines but you can browse through them)
> http://skagit.meas.ncsu.edu/~helena/gmslab/gsoils/movie/phb.mpg
> http://skagit.meas.ncsu.edu/~helena/gmslab/gsoils/movie/codbox.mpg
> http://skagit.meas.ncsu.edu/~helena/gmslab/gsoils/movie/phslice2.mpg
> they are explained here (still a draft document, after more than 12 years)
> http://skagit.meas.ncsu.edu/~helena/gmslab/gsoils/ccsoil2.html
> 
> Depending on your data generating the isosurfaces using -e or ln may help,
> at least for static figures.

> Browsing through the volumes should be much easier with wxnviz that saves settings
> into nviz_cmd command, so one can just loop the the isosurface values
> or crossection coordinates to generate the frames for the movie.

Helena
> 
> perhaps 9 slices by histogram of values?
> r3.univar precentile=`seq -s"," 5 10 95`
> ?
> 
> or is a linear split like for standard 2D contour lines less
> confusing for the viewer to understand?
> 
> (I'm working with heavily vertically stratified data and the
> linear approach isn't working very well)
> 
> 
> thanks,
> Hamish
>