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Re: [ferret_users] Modulo axis question

Hi Roman,
It's not an error, but just a minor warning. Anytime Ferret gives you something starting with *** NOTE, it is letting you know that you (or the dataset you've opened) has done something that could lead to unexpected results. That shouldn't really be a problem in this case.

Here, an x axis with units of degrees is assumed to have a modulo length of 360 degrees, unless the file tells us otherwise with the modulo attribute. The coordinates on the X axis in this file have bounds according to what you show, which define the edges of the grid cells. If there aren't bounds in the file Ferret compute bounds between the coordinate points. Ferret is telling you that the axis length, which is the distance from the lower bound of the first grid cell to the upper bound of the last grid cell, is slightly less than 360 degrees. Perhaps on creating a file, it wasn't take into account that the edges of the grid cells are what should match across the branch cut, not the coordinates. Or it can be just a precision error in the file.

Roman Tonkonojenkov wrote:
Dear Ferreters,

I have a question about modulo axis and hope that somebody competent can comment on this.
When I load up a NetCDF file, I get the following error:
 *** NOTE: Ignored modulo length exceeding axis length: XT
Would anyone be able to explain to me what this means and if this is an error?

Any comments would be very appreciated,
Many thanks,

I am using  NOAA/PMEL TMAP
FERRET v6.07 Linux(g77) 2.4.21-32 - 08/29/07 And here is axis info:
 name       axis              # pts   start                end
 XT        LONGITUDE          100mi   1.799E(1.8)          1.8W
   Axis span (to cell edges) = 360 (modulo length = axis span)

double XT(XT) ;
        XT:missing_value = 9.96920996838687e+36 ;
        XT:axis = "X" ;
        XT:long_name = "longitude of the t grid" ;
        XT:units = "degrees_east" ;
        XT:modulo = " " ;
        XT:point_spacing = "uneven" ;
        XT:bounds = "XT_bn! ds" ;

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