I am classifying an .adf wind resource map which I vectorised using the Polygonise tool (which worked very well). I have classified the data using the Graduated symbol renderer using Natural Breaks (Jenks) mode. Unfortunately although the Range column will take decimals, only columns with whole numbers will render. Does anyone know if there is a way to do this. Am using QGIS 1.7.3.
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Interesting. This looks like a bug. I can replicate your problem using the
Area column and manually adding classes which use decimal ranges. However if I use the [Classify] button to auto-populate the ranges it all works.
Investigating a bit further reveals the automatic ranges are floating point numbers with exponents, e.g.
2.29803e+10. If edit the class and strip
e+10 those polygons will no longer draw. At the same time the legend range changes from 22 trillion something to 2.2 something. So I venture to get your splits working right you'll need to figure out what the exponential equivalent to your desired decimal is.
On windows 7 this can be done with the built in Calculator program. Just fire it up, set View to Scientific, enter a decimal and than tap the [Exp] button.
To convert in python, try this:
>>> '%e' % 55.23 '5.523000e+01'
My error, I used the Classify button all along. The problem seems to be that the converted column, DN, has a precision level of 1 whereas I need something like ±0.2.