Re: RotatedMercator map projection

Hi Seth,

I am not sure I can visualize what you are trying to do. Can you send
the script and the data
or at least an image of what you have now?
  -dave

On Sep 16, 2008, at 12:56 AM, Seth McGinnis wrote:

> Ah! I get it now. I didn't realize they were different. Thank you!
>
> So, it turns out my data is actually rotated pole. I have lat2d &
> lon2d arrays, so the data is showing up in the right place on the
> map, but I want to use a map projection that will make it square.
> Any thoughts? In Ezmap terms, I believe it has non-zero PLAT &
> PLON. Is that what mpCenterLatF & mpCenterLonF specify for the
> normal Mercator projection?
>
> --Seth
>
>
>> 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
>>> ----
>>> _______________________________________________
>>> ncl-talk mailing list
>>> ncl-talk_at_ucar.edu
>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>
>

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Received on Tue Sep 16 2008 - 12:35:29 MDT