Re: [ferret_users] curious Ambiguous coordinates on Z axis

[David Wang <climater@xxxxxxxxx>]

Hi Peter,

Thanks for your response. I understand that. But how does it have anything to do with the vertical coordinate? If I get rid of the vertical coordinate, Ferret won't complain about whatever y I choose. For example,

yes? use "$FER_DSETS/data/levitus_climatology.cdf"
yes? use "./levitus_climatology.cdf"   ! two files are identical
yes? let/d=1 sst = reshape(temp[k=1],x[gx=temp]+y[gy=temp])
yes? let/d=2 sst = reshape(temp[k=1],x[gx=temp]+y[gy=temp])
yes? plot/y=0.5 sst[d=2]-sst[d=1]
yes? plot/y=0 sst[d=2]-sst[d=1]

Regards,
D.

On Fri, Oct 3, 2008 at 3:02 AM, Peter Szabo <szabpet83@xxxxxxxxx> wrote:

Hey David,

ferret warns you, because you didnt put in the exact coordinate, so it chooses the closest point:

yes? shade/y=0 temp[d=2]-temp[d=1]
 *** NOTE: Ambiguous coordinates on Z axis: TEMP[D=2]-TEMP[D=1]

yes? shade/y=0.5 temp[d=2]-temp[d=1]
yes? shade/y=-0.5 temp[d=2]-temp[d=1]

Ferret doesnt say a note, when you put command y=0.5 or y=-0.5 as these are valid points:
yes? show grid temp[d=1]
    GRID GMS1
 name       axis              # pts   start                end
 XAXLEVITR LONGITUDE          360mr   20.5E                19.5E(379.5)
 YAXLEVITR LATITUDE           180 r   89.5S                89.5N
 ZAXLEVITR DEPTH (m)           20 i-  0                    5000
 normal    T

For command y=0, ferret somehow chooses the y=-0.5 (0.5S). i dont know why not the y=0.5 (0.5N). But thats an other topic.

Peter

On Thu, Oct 2, 2008 at 5:41 PM, David Wang <climater@xxxxxxxxx> wrote:

Hi Ferreters,

It seems to me that if I load two netcdf files whose variables have the identical vertical axis, Ferret will still render them as different ones, and issue a warning message ("*** NOTE: Ambiguous coordinates on Z axis") when calculations are done among variables. I guess calculations are correctly done, but the message is somewhat misleading. Here is an illustrative example:

$ ln -s $FER_DSETS/data/levitus_climatology.cdf .
$ ferret
        NOAA/PMEL TMAP
        FERRET v6.1
        Linux(g77) 2.4.21-32 - 03/25/08
         2-Oct-08 11:10

yes? use "$FER_DSETS/data/levitus_climatology.cdf"
yes? use "./levitus_climatology.cdf"
yes? say `temp[d=1],return=zaxis`
 !-> MESSAGE/CONTINUE ZAXLEVITR
ZAXLEVITR
yes? say `temp[d=2],return=zaxis`
 !-> MESSAGE/CONTINUE ZAXLEVITR1
ZAXLEVITR1
yes? shade/y=0 temp[d=2]-temp[d=1]
 *** NOTE: Ambiguous coordinates on Z axis: TEMP[D=2]-TEMP[D=1]

Thanks,
David