[ferret_users] Changed behaviour in regridding one point axes

[Martin Schmidt <martin.schmidt@xxxxxxxxxxxxxxxxx>]

Hi,
I am trying to regrid a variable defined at a single point with two 
dimensions.
From one file I read a 2d-field "wet" that is 1 at ocean points and 0 
otherwise.
I define a new grid (for short notation)

define grid/like=wet[d=1] rgrid

Read the river data
use "with_coordinates/angola.nc"

rivers data are time series with a single latitude and longitude 
coordinate and a time axis

let runoff= RIVER_BENGO[gx=rgrid@sum,gy=rgrid@sum]

I would expect, that ferret searches, in which grid cell the river is 
and sets runoff to the data value.
Otherwise runoff should be zero.

This does not work, the river appears to be spread over an area. The sum 
over all grid
points is the correct data value.

I was playing around with the examples in the manual. For example:

yes? define axis/x=163e/npoints=1 x1pt
yes? let var_1pt = randu(x[gx=x1pt]) ! a random value at a single coordinate
yes? list var_1pt
            VARIABLE : RANDU(X[GX=X1PT])
            LONGITUDE: 163E
          .4914
yes? define axis/x=161e:165e:1 x5pt
yes? list var_1pt[gx=x5pt@max] ! same value embedded within 5 point axis
            VARIABLE : RANDU(X[GX=X1PT])
                       regrid: 1 deg on X@MAX
            SUBSET   : 5 points (LONGITUDE)
161E   / 1:     ....
162E   / 2:     ....
163E   / 3:  0.04804
164E   / 4:     ....
165E   / 5:     ....

This differes from the example in the manual and is wrong. The number 
should be .4914.
I am using ferret 6.03. An old version (5.41 for AIX gives the correct 
result,
but does not work too for the river example. 5.7 and 5.8 are wrong too.

What I am doing wrong with the river example?
Seems there is a bug in ferret 6. Version 6.01 gives the same result.

Greetings,
Martin