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
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