# Creating Anaglyphs from Nadir Images

Has anyone made an anaglyph photo from Nadir geospatial data? I have found some excellent examples of making anaglyphs in GIMP from digital photography. I would like to do a similar process with Nadir geospatial data. I have a 11km x 11km Nadir image of a TIN that I would like to convert into an anaglyph. I was wondering if I could apply a shift to one of the images (ie: shift one image X metres west and X metres north) to create the "left" image of the anaglyph. My question is related to the amount or percentage of the shift needed. Is there a mathematical way to calculate this, if I know my resolution, extent and scale?

My other thought was to simulate overlap by creating two images that have 60% or 80% overlap between the images. Has anyone successfully tried this?

Any help would be appreciated.

Thanks...

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The simplest way I have found is to render the TIN in a 3D package, drape the image over it, and display two overhead views from points slightly displaced in the horizontal direction. Render these in grayscale and combine them, dedicating one to the red band and the other to the other two bands (reduced slightly in intensity to balance the two pieces), producing a red-cyan anaglyph.

For instance, starting with a 7.5 minute USGS DEM (Albemarle South quarter quad in Virginia) I created a relief plot to serve as the image. Here are the left and right renderings:

Now in grayscale:

And finally combined into an anaglyph:

No calculations were needed: I just manipulated the 3D viewpoint to obtain the side-by-side views of the same 3D model.

NB You can check out the effect by shrinking this page a little and, with your head held vertically, staring at the first or second row of images. Relax your eyes until they cross. Soon there will seem to be three images in a row: left, center, and right, but they will be out of focus. The trick is to concentrate on the center without uncrossing your eyes. With patience--this takes only a few seconds when you have practiced before--the center image pops into focus and the 3D effect is apparent.

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I was able to create a simulated anaglyph within GIMP. I was able to complete this by increasing the canvas size by 5 pixels in the X and Y direction. Doing this twice makes two scences. The second scene (right image) you need to shift the image in the X and Y the number of pixels you increased the canvas by (5 pixels). With the two images you can make an anaglyph image within GIMP. This may not be the best approach, but it seems to work. If anyone has any other workflows that seem to work please share, as I would be very interested in seeing the difference.

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