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Re: Plot curved line on a globe projection [message #85347 is a reply to message #85346]

Sun, 28 July 2013 12:16

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

ljs15@fsmail.net writes:

> I want to plot some straight line sections on a gridded globe plot (i.e. a line joining two points with different lat/lon coordinates), but want these lines to follow the curve of the globe.
>
> I did a test (which I thought would work!) using the following code, but it just plots a straight line:
>
> ;Coordinates etc
> latcentre = 30
> loncentre = 0
> angle = 0
>
> ;Plot globe
> set_plot, 'ps'
> !p.font=0
> device, /encap, xsize=6, ysize=6, /inches
> loadct, 0
> map_set, latcentre, loncentre, angle, $
> /orthographic, /isotropic, /grid, /horizon, /noborder
> map_grid, latdel=5, londel=5, glinestyle=0, glinethick=0.5, color=cgcolor('black')
> oplot, [10,30], [30,50], color=cgcolor('black')
> device, /close
>
> Can anyone offer any help? Is there anything simple I'm missing? I've searched online, but only seem to be able to find posts related to contouring on globe plots.

You can use Map_2Points to get the points making up a great circle
route, but there won't be much difference. Here is an example. The green
line is a straight line, the red is equally spaced in distance, and the
blue is equally spaced in longitude.

;Coordinates etc
latcentre = 30
loncentre = 0
angle = 0

;Plot globe
;set_plot, 'ps'
;!p.font=0
;device, /encap, xsize=6, ysize=6, /inches
cgdisplay, 600, 600
loadct, 0
cgmap_set, latcentre, loncentre, angle, limit=[30, 0, 50, 40], $
/orthographic, /isotropic, /horizon, /noborder
cgmap_grid, latdel=5, londel=5, glinestyle=0, glinethick=0.5
cgPlotS, [10,30], [30,50], Color='grn7'; Straight line.
cgPlotS, Map_2Points(10, 30, 30, 50, DPath=1, NPath=50), $
Color='red' ; Evenly spaced in distance
cgPlotS, Map_2Points(10, 30, 30, 50, /RHUMB, NPath=50), $
Color='blue' ; Evenly spaced in longitude.
;device, /close
END

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")

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[Message index]

		Plot curved line on a globe projection By: Sir Loin Steak on Sun, 28 July 2013 11:19
		Re: Plot curved line on a globe projection By: David Fanning on Sun, 28 July 2013 12:16
		Re: Plot curved line on a globe projection By: Sir Loin Steak on Sun, 28 July 2013 13:00
		Re: Plot curved line on a globe projection By: David Fanning on Sun, 28 July 2013 13:36
		Re: Plot curved line on a globe projection By: Sir Loin Steak on Sun, 28 July 2013 13:45

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