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Re: Cylindrical map projection screwed up? [message #13518] Fri, 13 November 1998 00:00
Jonathan Joseph is currently offline  Jonathan Joseph
Messages: 69
Registered: September 1998
Member
ISOTROPIC keyword was set, though even if it were not,
I would still expect lines of longitude to be vertical
and lines of latitude to be horizontal, the only
difference without ISOTROPIC set should be that the
number of pixels in X degrees of longitude could then
be different than the number of pixels in X degrees of
latitude.

David Fanning wrote:
>
> Are you missing the ISOTROPIC keyword?
>
Re: Cylindrical map projection screwed up? [message #13519 is a reply to message #13518] Fri, 13 November 1998 00:00 Go to previous message
Jonathan Joseph is currently offline  Jonathan Joseph
Messages: 69
Registered: September 1998
Member
Hmmm.

It looks like this could be it. I had switched from a different
type of map projection and didn't look closely at those
numbers. I had been setting them to be the middle of the
range of latitude/longitude that I was looking at. However,
I'm not sure I understand what meaning they could have in
a cylindrical projection.

Thanks.

-Jonathan

Liam Gumley wrote:
>
> Jonathan Joseph wrote:
>> I've been doing some stuff using cylindrical map
>> projections using set_map. So, darn it, I expect
>> my lines of longitude to be vertical, and my lines
>> of latitude to be horizontal in the image.
>>
>> But, when I set the LIMIT keyword to just look
>> at a small portion of the globe, this is not
>> the case. In fact, I only get a true cylidrical
>> projection if the min and max latitude have the
>> same magnitude, ie. -30 to 30 degrees.
>
> Try this:
>
> map_set, 30, -80, limit=[20,-100,40,-60], $
> /cyl, /isot, /cont, /grid ; Bad result
>
> map_set, 0, -80, limit=[20,-100,40,-60], $
> /cyl, /isot, /cont, /grid ; Good result
>
> Cheers,
> Liam.
>
> ---
> Liam E. Gumley
> Space Science and Engineering Center, UW-Madison
> 1225 W. Dayton St., Madison WI 53706, USA
> Phone (608) 265-5358, Fax (608) 262-5974
> http://cimss.ssec.wisc.edu/~gumley
Re: Cylindrical map projection screwed up? [message #13521 is a reply to message #13518] Fri, 13 November 1998 00:00 Go to previous message
Liam Gumley is currently offline  Liam Gumley
Messages: 473
Registered: November 1994
Senior Member
Jonathan Joseph wrote:
> I've been doing some stuff using cylindrical map
> projections using set_map. So, darn it, I expect
> my lines of longitude to be vertical, and my lines
> of latitude to be horizontal in the image.
>
> But, when I set the LIMIT keyword to just look
> at a small portion of the globe, this is not
> the case. In fact, I only get a true cylidrical
> projection if the min and max latitude have the
> same magnitude, ie. -30 to 30 degrees.

Try this:

map_set, 30, -80, limit=[20,-100,40,-60], $
/cyl, /isot, /cont, /grid ; Bad result

map_set, 0, -80, limit=[20,-100,40,-60], $
/cyl, /isot, /cont, /grid ; Good result

Cheers,
Liam.

---
Liam E. Gumley
Space Science and Engineering Center, UW-Madison
1225 W. Dayton St., Madison WI 53706, USA
Phone (608) 265-5358, Fax (608) 262-5974
http://cimss.ssec.wisc.edu/~gumley
Re: Cylindrical map projection screwed up? [message #13524 is a reply to message #13518] Fri, 13 November 1998 00:00 Go to previous message
davidf is currently offline  davidf
Messages: 2866
Registered: September 1996
Senior Member
Jonathan Joseph (jj@scorpio.tn.cornell.edu) writes:

> I've been doing some stuff using cylindrical map
> projections using set_map. So, darn it, I expect
> my lines of longitude to be vertical, and my lines
> of latitude to be horizontal in the image.
>
> But, when I set the LIMIT keyword to just look
> at a small portion of the globe, this is not
> the case. In fact, I only get a true cylidrical
> projection if the min and max latitude have the
> same magnitude, ie. -30 to 30 degrees.
>
> Is this a bug? or am I missing something obvious.

Are you missing the ISOTROPIC keyword?

Cheers,

David

----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438, Toll-Free Book Orders: 1-888-461-0155
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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