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I have collected location point data and wish to display this on a web based map. It was collected using a Garmin Etrex GPS using the WGS84 datum. I wish to display the points using Ushahidi and have done so successfully. The site is here.

http://www.flamingocensus.com/ushahidi/

Unfortunately the points do not correlate to what I know they should be, I believe it is a projection error. The points are supposed to be on the edge of the lake. Any suggestions or pointers on how to translate the points in the current projection to my new one.

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Can you tell us where you expect them to be? If you can also post some snippet of raw data, that would be quite helpful –  Devdatta Tengshe Aug 8 '10 at 16:31
    
how far off of their true locations are the points? meters, or not even in the right general area? –  scw Aug 8 '10 at 17:19
    
The points need to be translated onto the lake edge, roughly 10km North Eastwards –  Mark Iliffe Aug 8 '10 at 17:21
    
I'm not saying that this is your case, but with a device I own, I need to flip the x and y coordinates –  dassouki Aug 9 '10 at 17:54

3 Answers 3

What kinds of projections does Ushahidi support? I would imagine raw GPS data in it's native projections are supported, but you should confirm first with Ushahidi. For projection problems, you will always need to know the projections used in both the source data and the display software. If a re-projection is needed, I think there are freeware tools to do this (maybe GPS babel?) but this is definitely present in COTS GIS software.

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It looks like you are using openstreetmap tiles which are in "Google Mercator" so I suspect that you can reproject your points using proj4 and epsg:900913 as a target.

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You'd do best to take this problem in two steps: first, verify that the data displays in a WGS84 map as expected, then perform the required conversion, if it does line up.

I'd try importing the data into Google Earth (instructions) or QGIS to insure they line up as expected. My guess is there may be an issue of conversion from DMS to decimal degrees or similar that's changing the positions, and would be a good place to start.

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