I am trying to use the point sampling tool plugin from QGIS to get some sea ice data (ranging from 0-1) from a GTiff raster layer (ESPG: 3411) for my sites (ESPG:4326) in the Arctic. But the sea ice values obtained are all 1.0000.

I have set the project CRS as ESPG: 3411 (with OTF), same as the raster layer.

The overlay looks fine as I can actually click individual points on the QGIS to obtain sea ice data value point by point but I have hundreds of points.


Problem is in the CRS. Layers geometry must be in same CRS (like in other overlay analysis). OTF (on the fly) transformation doesn't matter since it not change the gometry in the layer file.

You have to reproject your point layer (Layer --> Save as..) or raster image (Raster --> Projections --> Warp (Reproject)... to same CRS.

In other words you are now probably sampling "empty space" and you have to fit your data in same CRS.

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    OTF DOES matter. Turning it off would show that the layers don't align. And the point sampling tool sees the data in the same way, without OTF. – AndreJ Aug 20 '16 at 9:28
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    @AndreJ Yes you'r right, it's definetly worth mentioning. I meant that OTF doesn't matter for sampling point tool itself (algorithm process) since OTF only visualize data in chosen CRS and not changing the geometry. – Oto Kaláb Aug 20 '16 at 9:45

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