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How to you compare two layers in QGIS to get the positional accuracy?

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Is that a homework question? –  underdark Jun 6 '12 at 17:34
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I have done this when comparing collected GPS points to known positions. You want to use the distance formula Sqrt((x2 – x1)² + (y2 – y1)²).

What I did was to add two new columns (X2 and Y2) to my GPS points and populate those columns with the known X and Y coordinates. In my dataset I had the X and Y coordinates of my GPS data in columns X1 and Y1. Using the distance formula I was able to calculate the positional accuracy of my GPS points relative to the known reference locations.

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