Hello,
I am trying to fill missing data in daily temperatures via v.surf.idw interpolation. I have imported daily temperatures via v.in.ascii to a latlong location, with missing values indicated by "", as suggested by Hamish:
http://www.intevation.de/rt/webrt?serial_num=2763&display=History
Then I have v.surf.idw interpolated the vector point values, both in the latlong import location and in a Lambert Conformal Conic (LCC) location, uploading raster values at positions of vector points to the attribute table via v.db.addcol & v.what.rast.
Following is an excerpt of the attribute table I have obtained, where TEMP is the daily temperature at a particular LON and LAT, while SURF1 and SURF2 are values uploaded from interpolated raster in the latlong and LCC locations, respectively (I have added the MISSING flag to indicate a missing temperature value, which is a "" in the real table, for clarity):
CAT | LON | LAT | TEMP | SURF1 | SURF2
1 | 8.283300 | 40.633300 | 14.600000 | 6.585142 | 7.339586
2 | 16.314700 | 40.283100 | MISSING | 11.720935 | 11.169486
3 | 11.850000 | 43.466700 | 12.000000 | 8.832849 | 9.011710
In the help, I read that v.surf.idw generates the interpolated surface from the data points.
Would this mean that the interpolated raster pass exactly through the vector input points (i.e., uploaded values should equal original input values), contrary to v.surf.rst where the smooth paramenter controls the deviation between the given points and the resulting surface?
Thanks and regards,
Luigi