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Question about projection for Google Earth [message #85453]

Thu, 08 August 2013 19:11

timothyja123
Messages: 57
Registered: February 2013

Member

Hi Guys,

I'm trying to finish off some unfinished code that wasnt written by me. I'm fairly new to using projections, mapping, etc in IDL but from what I understand to map an image to Google Earth I need to use something like:

mapStruct = MAP_PROJ_INIT( 117 , /GCTP, limit=limit) ; Equirectangular projection
xy = Map_Proj_Forward(lon, lat, MAP_STRUCTURE=mapStruct)
lon = Reform(xy[0, *])
lat = Reform(xy[1, *])

The problem is that my lon/lat values contain a different number of values and Map_Proj_Forward() is complaining about this. Whay do they need to be the same? My overlay is a rectangular shape rather than a square why can this no be handled?

The code that I was left with does something like this but the image doesnt overlay correctly on Google Earth I assume this is because it uses the incorrect projection.

limit = dblarr(4)
limit[0] = min(lat)
limit[1] = min(lon)
limit[2] = max(lat)
limit[3] = max(lon)

polon = limit[1]+0.5*(limit[3]-limit[1])
map_set, 0,polon,0,/cyl,limit=limit, /noborder, xmargin=0,ymargin=0

contour, values*mask,lon,lat, levels=levels,C_color=c_levels,/overplot,c_labels = 0,/cell_fill, min_value = 2

hamax = 0 & bathy_mask = 0 & lat = 0 & lon = 0

most_image = tvrd()
Device, close = 1

; output image to a PNG file with transparency
name = 'test.png'
outputOverlayFile = filepath(name, root_dir=sourcepath(), subdir=['output'])

; set transparency
idx = where(most_image LT 240, trans_count)
if trans_count GT 0 then begin
write_png,outputOverlayFile ,most_image, r2,g2,b2, transparent=idx
endif

Anyhelp or tips on this would be greatly appreciated. I have looked at some of David Fanning's guides on creating images for Google Earth but could find anything on this exact issue.

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[Message index]

		Question about projection for Google Earth By: timothyja123 on Thu, 08 August 2013 19:11
		Re: Question about projection for Google Earth By: David Fanning on Thu, 08 August 2013 19:26
		Re: Question about projection for Google Earth By: timothyja123 on Thu, 08 August 2013 21:50
		Re: Question about projection for Google Earth By: David Fanning on Fri, 09 August 2013 03:51
		Re: Question about projection for Google Earth By: timothyja123 on Sun, 18 August 2013 22:04
		Re: Question about projection for Google Earth By: Fabzi on Mon, 19 August 2013 00:27
		Re: Question about projection for Google Earth By: David Fanning on Mon, 19 August 2013 05:26
		Re: Question about projection for Google Earth By: timothyja123 on Sun, 01 September 2013 22:15
		Re: Question about projection for Google Earth By: David Fanning on Tue, 03 September 2013 06:03

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