[STATSGRASS] unfilled matrices with R and gstat in grass 6.2.0beta3

[roger at spinn.net]

Folks, 

This is a user's question, rather than a developer's question. 

I have R with the gstat library working with grass6.2.0beta3.  On Linux 
2.6.13 x86_64 (SuSE 10.0).  The software generally works and I can confirm 
its results at least approximately against other software.  The problem I'm 
having is that the resulting map is sometimes not completely filled.  I get 
calculated values on diagonal lines in the map and the intervening areas are 
left unfilled -- they have null values.  The same pattern is visible whether 
I look at the result from within R or export the result to a grass raster 
file. 

The pattern is not so simple as a limit to the size of the resulting map.  I 
have a small set of data (about 60 locations) and need to construct a map of 
an area of about 20x30 km, using a grid with spacing of 30mX30m.  The 
resulting map should have 686736 values, but the the result only contains 
171684 non-null values.  That is exactly 1/4 of the cells.  If I increase 
the cell area to 60mX60m so that the grid only contains 171684 cells, then 
the result contains 85842 non-null values.  That is 1/2 of the cells. 

I can construct a map using 16 tiles across the same area and patch them 
together to get a completely filled map, but for most purposes that is an 
excessive amount of work. 

With a different data set with about 250 points and trying to construct a 
map over a larger area using a grid with 169576 cells, each 120mX120m I do 
get a filled raster map in the result, though the result looks a little odd. 

I don't understand what is happening and I've found no mention of this 
problem elsewhere.  Any ideas? 


Roger Miller