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    Guild Journeyer Facebook Connected EricPoehlsen's Avatar
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    Mar 2011
    Regensburg, Germany

    Question Image to GIS - what the hell

    Hi together, I am experiencing a strange phenomenon while trying to create a real-GIS map for some fantasy project.

    I do have multiple raster and vector sourcemaps - my main working map is currently an inkscape svg. which is at 7 units per kilometer - yeah that is a little strange but it is what happened in tracing the original old rasterfile.

    It is an island which is roughly 400km north to south and 270 km east to west. measuring in inkscape i get 418kms and 266kms between significant points. The area calculation returns roughly 70.000 km². The Island is situated at the northern hemisphere between 46°N and 50°N.

    So I created an image overlay in googleearth and resized it that i measure the significant points at +- 2km of my inkscape measurements. I wrote down the corner coordinates and used them to create an geocoded tiff. I tried tons of tools - the QGIS geocoding returned anything but useful results, the MapWindowGIS geocoder didn't work at all but I finally managed to create a working geocoded tiff with QLandkarteGT

    Next step, I imported the geocoded tiff into QGIS and measured the two distances. The distance was nearly what it should be 418 kms and 266kms respective. So I created a new shapefilelayer and did a fast tracing of the outline - went to the measurement-tool and got an area of 154.000 km²

    Anyone here an idea what the hell went wrong there?! I did the tiff geocoding again, I did the tracing again and ended up with another shape which has the same east-west north-south dimension but returns more than double the expected area!
    Last edited by EricPoehlsen; 07-28-2012 at 07:11 AM.

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