Re: RotatedMercator map projection

Hi Seth,
The RotatedMercator projection is not actually the same as a rotated
pole projection. It ignores the 'mpCenterLatF' value,
and the 'mpCenterRotF' value behaves in a different manner from the
normal Mercator projection.
You will see the difference if you give 'mpCenterRotF' a non-zero value.

For an explanation of the difference between these projections from
the perspective of the underlying software, see:

http://www.ncarg.ucar.edu/supplements/ezmap/#PROJECTIONS

Scroll down to 'Cylindrical Projections'

If the grid is plotted in its native projection then you must either
have the tfDoNDCOverlay flag set True, or you are not communicating
the 2d coordinates correctly to the plotting routine.

  -dave

On Sep 15, 2008, at 4:17 PM, Seth McGinnis wrote:

> Does anyone have any examples of how to plot data that's in a
> rotated Mercator (aka rotated pole or rotated lat-lon) coordinate
> system?
>
> I've been making plots using the following map projection resources:
>
> res_at_mpProjection = "RotatedMercator"
> res_at_mpCenterLonF = 83
> res_at_mpCenterLatF = 42.5
>
> and as far as I can tell, it doesn't look any different than
> leaving the projection unspecified. (The data has lat2d and lon2d
> arrays. Using the same attributes with the corresponding values
> for data in a polar stereographic or transverse mercator projection
> results in the native grid being plotted square on the page.)
> Maybe I have the wrong values there, but I tried it with
> mpCenterLatF = 0, 45, and 90, and it made no difference to the
> resulting plot. Should I be specifying the projection parameters
> in a different way?
>
> The only examples I can find of the RotatedMercator projection on
> the NCL website are in the "Map Only" application examples 12 & 13,
> and it looks to me like the RotatedMercator example is identical to
> the Mercator example.
>
> Thanks,
>
> --Seth
>
> ----
> Seth McGinnis
> Associate Scientist
> ISSE / NCAR
> ----
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Received on Mon Sep 15 2008 - 17:37:40 MDT