[GRASS-user] Re: [GRASS-dev] r.in.xyz upgrade

[Glynn Clements]

Hamish wrote:

> > I have upgraded r.in.xyz to allow for the following aggregate functions:
> > - skewness
> > - median
> > - percentile
> > - trimmed mean
> > 
> > To make this possible, I created singly linked lists for all points 
> > falling into a cell. I followed a suggestion of Glynn and used arrays 
> > instead of pointers and stored the head of each list in a raster map 
> > ([GRASS-dev] storing pointers in CELL_TYPE maps? (from April 2007)).
> > The linked lists are then used to calculate the corresponding
> > statistics before binning the values.
> > So far we encountered no problems with this approach in our working 
> > group, but I'm not sure about some details. Maybe there should be some 
> > more checks, e.g. to prevent the index to overflow because of too many 
> > cells.
> 
> [Gf patch #450]
> 
> After a long delay I have finally applied the patch in GRASS
> 6.3-CVS/HEAD.
> 
> I apologize to Volker for taking so long to deal with this, and
> congratulate him and his team on a job well done. It's a nice little
> bit of code.
> 
> The memory footprint seems to be about the same as for a stddev map.
> 
> 
> Question for the LFS folks: if the region size is >2/4billion cells*
> will the num_nodes, max_nodes, and node.next variables want to be
> something larger than int? nb I expect there will be other memory
> issues in this case anyway, and multi-pass via the percent= option
> should be used. * regions bigger than 45000x45000 / 63245x63245
> 
> 
> aside:
> I am finding the r.colors "-e" flag and the 'r.colors.stddev -z'
> add-on script very very useful these days. ('r.colors -e' for
> ignoring outliers and 'r.colors.stddev -z' for a proper differences
> map [method=skewness])
> 
> 
> go forth and test it,
> Hamish
> 
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