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Re: Longitude weirdness

Hi Joe,

On Fri, 27 Jun 2003, Joe McLean wrote:

> Is the longitude axis a regular or irregular axis (equal or unequal steps)?  In
> Ferret you can tell by opening the data set and using the command "show grid
> varname"
> ie
> name             axis                        # pts    start                  end
> xaxis name    LONGITUDE          180mr   21E                  19E(379)
> next to # pts 180, 'm' means modulo and 'r' means regular (i means
> irregular).  The fact that your XML file does not have the arange tag,
> but rather the <v>20.140625</v> format, tells me LAS thinks it is
> irregular, but this may be a precision issue within addXml.pl.  The
> first two steps are each 0.2812, it may be regular.

Ferret shows LONGITUDE as mi so it is modulo irregular.  However, it does
appear to actually be a regular grid with points every .28125 degrees

> Since the axis in the NetCDF file is modulo, it wouldn't matter which start point
> you use in the XML axis definition.
> if the axis is irregular, subtract 20 from all of the <v>.....</v> entries.
> If the axis is regular, you can define your axis in the XML file like this:
>    <mf1_11b_19990515_nc_longitude units="degrees" type="x">
>        <arange start="0.0" step = "0.2812" size="1280"/>
>    </mf1_11b_19990515_nc_longitude>
> In fact, try it this way first (less editing) and see if you like the way LAS
> responds.

That works!  I used a step of 0.28125 and it works very well. Should I
just count on hand editing this? It isn't a big deal.  I don't think there
will be that many data sets.  I will be creating the netCDF files so if
there was something I could put in there to help trigger the make file to
do this then that would be ideal but either way I'm just glad something

> By the way, starting the the longitude values at 20 E is for drawing the world by
> bisecting Africa at the left and right sides of a plot window, keeping ocean basins
> contiguous.

Makes perfect sense now.

Thanks very much for your help with this.


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