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

[Hamish]

[Back in July!] Volker Wichmann 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