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Re: read lambert projected image [message #88800 is a reply to message #88799]

Sat, 21 June 2014 11:30

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

audrey.schaufelberger@gmail.com writes:

> I am afraid I don't quite understand what you mean... I have an image showing the farside of the moon. The complete farside, so I know that the map ranges from 90...270 deg in longitude and from -90...90 deg in latitude. I also know that the projection used is a lambert equal area projection. In addition, the map fills the image, i.e., (90/0) deg touches the left center, (180/90) deg the top center, (270/0) deg the right center and (180/-90) deg the bottom
center of the image. So in theory I guess, since everything seems well defined, I should be able to determine the lon/lat pair corresponding to a x/y image coordinate. I was hoping there was a procedure where I can tell what projection a map is plotted with, and the procedure would read the .jpg while assigning each x/y image coordinate the right lon/lat coordinate.
> but that might be a bit much I ask for..

With a JPEG image, you are asking for too much. Can you find the same
image in a GeoTiff image format? That will have the map projection
information you need built into it. Failing that, NASA (or whoever
created the original image) usually have information about the map
projection used, etc. Since this is the moon, you will need to know its
radius, and what kind of Geoid (sphere, ellipsoid, etc) was used to
determine the latitude and longitude points. It wouldn't surprise me if
the organization that captured the image has already created latitude
and longitude arrays for every image pixel. Have you looked for these?

Cheers,

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

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[Message index]

		read lambert projected image By: audrey.schaufelberger on Fri, 20 June 2014 10:56
		Re: read lambert projected image By: David Fanning on Fri, 20 June 2014 14:09
		Re: read lambert projected image By: audrey.schaufelberger on Sat, 21 June 2014 09:56
		Re: read lambert projected image By: David Fanning on Sat, 21 June 2014 11:30
		Re: read lambert projected image By: audrey.schaufelberger on Sat, 21 June 2014 15:15
		Re: read lambert projected image By: David Fanning on Sat, 21 June 2014 20:56

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