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I thought I followed the QGIS geo-reference tutorial in precisely.

The following raster (with our overlay) was snapped from GoogleEarthPro (I believe that Google Earth is using EPSG 4326, not WebMercator as is GoogleMaps).

I created 5 place marks, and got the decimal lat/long.

I put them into QGIS 2.10 Georeferencer Picture below.

Tried all variants of settings (Linear, Thin Plate) as well as EPSG 4326, and 3857 output), as well as Linear and Nearest Neighbor Resample.

output is to a GeoTiff.

But the issue still is that you can see that the image is stretched in the X axis.

Now, maybe I should not be viewing in an image viewer (IRFan). And that is my problem.

For when I have (Thin Plate Spline, Linear resample, GeoTiff in EPSG 4326) and view the data in FME Data Inspector, it does look ok!!

All I really want is to read the data out from FME Data Inspector for the Corners points in Lat/Long. So Tell me if I am actually doing things correctly, and the only stupid thing is viewing with IRFAN.

Also given that this is a very small area, what are the best georeference settings for maximum precision?

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Yeah... a georeferenced TIFF is NOT going to look right in a normal image editor. EPSG:4326 noticeably distorts horizontally if it is not actually projected to its coordinate system.

For emphasis: Don't view raster GIS/spatial data in a normal image editor!!

As far as highest precision georeferencing, since it is such a tiny area, precision is not really a big deal. You could do it in a projected coordinate system if you wanted (UTM zone etc.) but at this scale the errors are going to be miniscule anyways, your strategy as outlined above should be fine.

  • And is it true that Google Earth uses EPSG 4326, and Google Maps Imagery is in 3857. What is odd is they look the same to my eyes, which is why I ask. – Dr.YSG Oct 20 '15 at 17:38
  • That's because those projections are almost exactly the same. 4326 uses lat/lon and an ellipsoid earth model. 3857 uses x,y (meters) and a spherical model. At small scales the difference will be unnoticeable. – Thomas Oct 20 '15 at 17:57

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