# Digital Elevation Maps (DEM) are Warped yet ReliefPlot renders as a rectangle - how do i join?

I downloaded several USGS Digital Elevation Maps (DEM files) corresponding to 12 adjacent areas. Each file Imports[] into Mathematica and I can render the individual ReliefPlots easily. The intent was, however, to create a mosaic by joining the individual images. Unfortunately, each DEM is warped and when I render using ImageAssemble there are triangular gaps between each ReliefPlot.

Does anyone know if there is a simple way of using Mathematica to orthogonalise the tiles so they can be assembled without gaps? It seems like Import pads the gaps using a number corresponding to a corner thereby creating an array that can be processed by ReliefPlot.

I gather the issue stems from fact each tile is a quadrangle defined using UMT coordinates so I'm hoping the Geodesy package will help effect the transformation. However, having looked at the Geodesy functions I can't see the wood for the trees! Is there a simple fix. And is there a tutorial or book for the package?

-
It would be helpful if you linked some data and actual code you used together with an image to show how the triangular gaps look. In the meantime, there is quite a lot of how-to's in this blog that might help you. –  gpap Mar 20 '13 at 10:01

There is a Wolfram Blog post that explains this as a subproblem:

Mapping GPS Data, by Robert Raguet-Schofield.

That was published in 2009 and I think is pretty nifty. But I'd recommend looking into out new URLFetchAsynchronous and perhaps updating the code. Below you see parts in the blog where he seamlessly goes from patches to a single map:

-