[GRASS-dev] v.univar question: Why not lines and areas?

[Moritz Lennert]

On 27/01/08 20:30, Michael Barton wrote:
> v.univar only works with points. But since it is calculating stats on a 
> field in the attributes table, it should work the same for all vector 
> objects. Can we get rid of the limitation that it only works with points?

There was some debate [1] about the statistical validity of working with 
the other types, as the way it was programmed, the statistics were 
calculated with weights which corresponded to line length / area surface .

I guess we might want to distinguish between a v.univar which works on 
the actual vector objects from a v.db.univar which works on any 
arbitrary attribute (or combination of attributes). We could write a 
C-replacement of the current v.db.univar script on the base of the code 
I have for the classification algorithms used in v.class.

As mentioned earlier, it might be better that I move the code from 
v.class into a library which can then be accessed by different modules...

Currently, I have defined the following statistics:

typedef struct
{
     double count;
     double min;
     double max;
     double sum;
     double sumsq;
     double mean;
     double var;
     double stdev;
} STATS;


But this could easily be extended according to needs and v.db.univar 
could also use the quantile classification algorithm to extract percentiles.

What are the statistics most people need ?

Moritz

[1] http://lists.osgeo.org/pipermail/grass-dev/2004-July/014976.html