[Qgis-user] Raster Calculator Expression to determine color

[Nick Papadonis]

> On Jul 30, 2015, at 9:29 PM, Nyall Dawson <nyall.dawson at gmail.com> wrote:
> 
> 
> On 31 Jul 2015 11:07 am, "Nick Papadonis" <npapadonis at gmail.com <mailto:npapadonis at gmail.com>> wrote:
> >
> > HI Folks,
> >
> > I’m trying to use the following expression to pick up the red colored routes on a map in which I used the info pointer tool to get the band values for the color.
> >
> > (“m at 1" < 238 AND “m at 1" > 213 AND “m at 2" < 123 AND “m at 2" > 98 AND “m at 3" < 125 AND “m at 3" < 99) * 1
> 
> Should that last check be "m at 3" > 99?
> 
> 
Yeah, I changed that and still same results.  If I specify on > and remove the < expressions, then everything works.  Very odd considering the color is within the range above (with the line you referenced fixed).

Thanks
> Nyall
> 
> >
> > Unfortunately, when this expression is used the resulting map is black with no other pixels for the detected color.
> >
> > If I break down this expression to a simple “greater than” line for single band, then things work.
> >
> > Does anyone know where this expression needs to be corrected?
> >
> > Thanks again,
> > Nick
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