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I am evaluating QGIS with a view to visualize and manage geological exploration data. The information is currently stored in different local coordinate systems that I am looking to overlay with satellite imagery from Google and Bing. I figured out how to load the data I want into QGIS, but I am struggling to find a way to convert them into a common coordinate system?

I presume I should use geographical coordinate system like WGS84. Is anyone can explain what tools are available for conversion from a local projected coordinate system (I believe it is a Mercator based projection) to latitude/longitude using few reference points where I have coordinates in both systems?

I tried to follow suggestion from here: How to georeference a vector layer with control points? and downloaded Affine Transformation Plugin. But I cannot figure out how to get the input parameters (scale, translation and rotation) without mastering coordinate projections theory. I have not tried v.transform that was also suggested as I could not see how to make it work for geographical coordinates.

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user20763
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I would suggest to split up the data into as many files as you have local CRS.

Then you can assign the CRS to the layers, and reproject the data in QGIS with Rightclick -> Save as into a common CRS.

Or simply create a new layer in WGS84, and copy and paste the other data into it on the screen.

If you can supply sample coordinate pairs in local CRS and lat/lon, we could figure out the local CRS used.

AndreJ
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  • The ultimate goal is to have the raw data in an mysql database. I have a few exploration sites that all use their own local CRSs. Thank you for the offering to work out the conversion parameters for me but unfortunately it will not be practical. I need to automate conversions whether in a query in the database before loading them or setting up a conversion in QGIS. I thought there will be several available tools in QGIS to automate these conversions. I should be able to get conversions parameters from local CRS to UTM if this will help. – user20763 Aug 06 '13 at 11:14
  • Usually, CRS are defined by their EPSG codes, and QGIS can do the reprojection between known EPSG codes. If you want one table with different CRS, you might end up doing it programatically. – AndreJ Aug 06 '13 at 11:27
  • It seems I will need to convert my local CRSs into one that QGIS can recognize within the database and then do "on-fly" re-projection to WGS84. It should be doable. Thank you for your help. – user20763 Aug 06 '13 at 11:42