Thanks for the reply On 8 May 2012 12:11, Rainer M Krug <[email protected]> wrote:
> > > > I do EMPA ( Electron probe micro-analyzer ) of microscope slides. When > it is in the device I > > can note down x,y,z co-ordinates when taking a photo or doing a sample > analysis. The problem is > > when you remove the slide and put it back in again these previous x,y > and z components are now > > meaningless because the device that holds the slide is not accurate > enough to achieve the same > > positioning again. I was thinking that if I had known reference points > on the slide I could > > "geo-reference" all pictures and scans I did for a specific session and > then when I have follow > > up photos and point analysis data, taken in a separate session, I could > "geo-reference these > > and use QGIS to map out all the photos and pin point analysis as > different layers making it > > very easy to correlate data. As long as I have the co-ordinates I should > then be able to add > > any other microscope ( eg. petrographic images ) data as a separate > layer and match it up. > > > Sure - you can "geo-reference" whatever image you have against whatever > system. In your case, yo > should be choosing the right co-ordinate system and the right projection. > This is something I > can't help you with at the moment, but it should be easy enough to find > out. If in doubt, ask > specifically for this again, as it is of uttermost importance for > measuring distances, areas, > calculations and so on. > All true, but at least it sounds possible. The images I am mapping is square so another thing to consider in my co-ordinate and projection system. > > One definitely has to be aware, that the space of the GIS, which is > usually the surface of the > earth (or a section of it) can be anything. It can simply be a piece of > paper or, in your case, > the area *flat* area which is seen in the EMPA. And you want to reference > your slide to the area, > so that a specific point of the slide is always at the same location - > look at it as satellite > pictures: the earth is your slide, and the satellite is your EMPA (OK - > the earth is not flat, but > this is where the projection comes in). > > > > > If I could get it working I could also write a plugin that could tell me > co-ordinates of a > > point on the "map" based on the new x,y co-ordinates when I re-insert > the microscope slide. > > Just in case it is not clear let me explain: When I insert a slide into > the EMPA machine a > > certain spot will have co-ordinates of 255,234,40. When I re-insert the > slide it might now have > > co-ordinates of 100,2000,80. However it is still the same point but > because I am measuring in > > nano meters small changes can make big differences. > > Just to be sure - you have three co-ordintes here? then it might be a > problem - but if you only > want to geo-reference the *picture* of the slide into a two dimensional > flat surface, that should > work easily. > I do have 3 co-ordinates but for the work that we do at least for now the y-co-ordinate is not really important so should not be a problem. > > > > > My question is thus, does this sound possible and have anyone else done > something similar? The > > area being mapped is actually flat and I am not sure if that would make > a difference. > > 1) The area being mapped is flat > 2) are all areas parallel? > > Yes the area being mapped is flat for practical intents and purposes. and everything should be parallel. Although some images might need rotation since it is not possible on a micron meter scale to align up a microscope slide exactly parallel. I am planning on doing a lot more work on this later in the summer and will report back to the list of results and any more questions which I might have. Regards -- Gerhardus Geldenhuis
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