4 replies to this topic

[eruheru]

Hello,
I am a new GIS user working on a project on Lake Turkana in Kenya. Right now the DEMs I am working with are unprojected (WGS 1984). I would like to project them to make reliable Hillshades, however I am unsure of which projection to use. The original plan was to use UTM Zone 37. Today I noticed that part of the lake and watershed fall into the next zone. I would prefer, from a data management perspective, to keep everything in the same projection. Any suggestions would be incredibly appreciated.

Thanks!

[Martin Gamache]

Use a Tranverse Mercator, centered on your AOI. Or if you are using alot of Landsat Imagery, pick one of the UTM zones (the larger one in your coverage area and reproject everything else to it. This will save you from having to reproject two sets of imagery datasets.

MG

[frax]

Why wouldn't you be able to create accurate hillshades in WGS84? You just have to remember that your GIS software might think that the z-values are in decimal degrees, and calculate based on that (for the vertical exaggeration).

[eruheru]

Using a single UTM zone wouldn't cause problems?

@frax - I was able to use the conversion factors on the z-values to get a good result but I would like to be as accurate as possible. I figured a projection would give the best result.

Thanks for the help

[frax]

eruheru - projecting the data won't necessary make the result more accurate. Keep in mind that a reprojection also means resampling the data. The most accurate (as in true to the original dataset) would be to create the hillshade in the original projection, and then reproject the resulting gray scale image.

Since Kenya is on the equator, WGS84 does not present any distortion, as it would on higher latitudes.