Re: [Matplotlib-users] Basemap projection issue

[Jeff W. <js...@fa...>]

Adam Mercer wrote:
> On 11/10/2007, Jeff Whitaker <js...@fa...> wrote:
>
>   
>> Adam:  I assume your data is on a latitude-longitude grid?  You've asked
>> for a mollweide projection centered on the Greenwich meridian.  Your
>> data is not centered on Greenwich - but the error message is trying to
>> say that you can shift your grid (with the shiftgrid function) so that
>> is has the same orientation as the map projection region.  This only
>> comes into play with global projections that 'wrap-around' at the edges,
>> like the mollweide and mercator projections.  The orthographic
>> projection does not 'wrap around' - hence you don't get the error message.
>>     
>
> Looking at the shiftmap function it looks like I should shift the
> co-ordinate grid so that my longitude runs from -180 to 180 instead of
> 0 to 360, therefore the following shiftgrid call should do this
>
> values, lon = basemap.shiftgrid(180, values, lon)
>
> However I still get the same error and the corruption in the resulting
> plot.  I feel like I'm missing something obvious here but can't find
> it.
>
> Cheers
>
> Adam
>   
Adam:

 From the basemap docs;

shiftgrid(lon0, datain, lonsin, start=True)
    shift global lat/lon grid east or west.
    assumes wraparound (or cyclic point) is included.
     
    lon0:  starting longitude for shifted grid
           (ending longitude if start=False). lon0 must be on
           input grid (within the range of lonsin).
    datain:  original data.
    lonsin:  original longitudes.
    start[True]: if True, lon0 represents the starting longitude
    of the new grid. if False, lon0 is the ending longitude.
     
    returns dataout,lonsout (data and longitudes on shifted grid).


You did

values, lon = basemap.shiftgrid(180, values, lon)

but I think you want

values, lon = basemap.shiftgrid(180, values, lon, start=False)

HTH,

-Jeff

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