[prev in list] [next in list] [prev in thread] [next in thread]
List: qgis-user
Subject: Re: [Qgis-user] Raster Calculator Expression to determine color
From: Nick Papadonis <npapadonis () gmail ! com>
Date: 2015-07-31 1:56:24
Message-ID: D3B07492-EEB4-47A3-8662-814EA7B0E2F2 () gmail ! com
[Download RAW message or body]
[Attachment #2 (multipart/alternative)]
> On Jul 30, 2015, at 9:29 PM, Nyall Dawson <nyall.dawson@gmail.com> wrote:
> On 31 Jul 2015 11:07 am, "Nick Papadonis" <npapadonis@gmail.com \
> <mailto:npapadonis@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@1" < 238 AND "m@1" > 213 AND "m@2" < 123 AND "m@2" > 98 AND "m@3" < 125 AND \
> > "m@3" < 99) * 1
>
> Should that last check be "m@3" > 99?
>
>
I corrected above to:
("m@1" < 238 AND "m@1" > 213 AND "m@2" < 123 AND "m@2" > 98 AND "m@3" < 125 AND "m@3" \
> 99) * 1
with the same results which is black output tiff.
I then tried individual expressions for each band as separate steps (sanity check):
("m@1" < 238 AND "m@1" > 213) * 1
("m@2" < 123 AND "m@2" > 98) * 1
("m@3" < 125 AND "m@3" > 99) * 1
These all produce a masked image, however masked incorrectly because I'm evaluating \
only a single band in the Raster Calculator.
When I combine evaluation of bands as above or below to pick pixels in color range:
(("m@1" < 238 AND "m@1" > 210) AND ("m@2" < 123 AND "m@2" > 94) AND ("m@3" < 130 AND \
"m@3" > 98)) * 1
I get a black image with no matches. I expected at least one pixel identified using \
this expression because I evaluate a pixel at 224, 108, 115 and there are many other \
pixels in above range.
Does anyone know if my expression needs correction or the Raster Calculator can only \
evaluate a single band in the expression?
Thanks again,
Nick
> 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
> > _______________________________________________
> > Qgis-user mailing list
> > Qgis-user@lists.osgeo.org <mailto:Qgis-user@lists.osgeo.org>
> > http://lists.osgeo.org/mailman/listinfo/qgis-user \
> > <http://lists.osgeo.org/mailman/listinfo/qgis-user>
[Attachment #5 (unknown)]
<html><head><meta http-equiv="Content-Type" content="text/html \
charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; \
-webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote \
type="cite" class=""><div class="">On Jul 30, 2015, at 9:29 PM, Nyall Dawson <<a \
href="mailto:nyall.dawson@gmail.com" class="">nyall.dawson@gmail.com</a>> \
wrote:</div><div class=""><p dir="ltr" class="">On 31 Jul 2015 11:07 am, "Nick \
Papadonis" <<a href="mailto:npapadonis@gmail.com" \
class="">npapadonis@gmail.com</a>> wrote:<br class=""> ><br class="">
> HI Folks,<br class="">
><br class="">
> 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.<br \
class=""> ><br class="">
> ("m@1" < 238 AND "m@1" > 213 AND "m@2" < 123 AND "m@2" > 98 AND \
"m@3" < 125 AND "m@3" < 99) * 1</p><p dir="ltr" class="">Should that last check \
be "m@3" > 99?</p><div class=""><br class=""></div></div></blockquote><div><br \
class=""></div><div>I corrected above to:</div><div>("m@1" < 238 AND "m@1" > \
213 AND "m@2" < 123 AND "m@2" > 98 AND "m@3" < 125 AND "m@3" > 99) * \
1</div><div><br class=""></div><div>with the same results which is black output \
tiff.</div><div><br class=""></div><div>I then tried individual expressions for each \
band as separate steps (sanity check):</div><div>("m@1" < 238 AND "m@1" > 213) \
* 1</div><div>("m@2" < 123 AND "m@2" > 98) * 1</div><div>("m@3" < 125 AND \
"m@3" > 99) * 1</div><div><br class=""></div><div>These all produce a masked \
image, however masked incorrectly because I'm evaluating only a single band in the \
Raster Calculator.</div><div><br class=""></div><div>When I combine evaluation of \
bands as above or below to pick pixels in color range:</div><div><br \
class=""></div> (("m@1" < 238 AND "m@1" > 210) AND ("m@2" < 123 AND \
"m@2" > 94) AND ("m@3" < 130 AND "m@3" > 98)) * 1</div><div><br \
class=""></div><div>I get a black image with no matches. I expected at least \
one pixel identified using this expression because I evaluate a pixel at 224, 108, \
115 and there are many other pixels in above range.</div><div><br \
class=""></div><div>Does anyone know if my expression needs correction or the Raster \
Calculator can only evaluate a single band in the expression?</div><div><br \
class=""></div><div>Thanks again,</div><div>Nick</div><div><br class=""><blockquote \
type="cite" class=""><div class=""><p dir="ltr" class="">Nyall</p><p dir="ltr" \
class="">><br class=""> > Unfortunately, when this expression is used the \
resulting map is black with no other pixels for the detected color.<br class=""> \
><br class=""> > If I break down this expression to a simple "greater than" \
line for single band, then things work.<br class=""> ><br class="">
> Does anyone know where this expression needs to be corrected?<br class="">
><br class="">
> Thanks again,<br class="">
> Nick<br class="">
> _______________________________________________<br class="">
> Qgis-user mailing list<br class="">
> <a href="mailto:Qgis-user@lists.osgeo.org" \
class="">Qgis-user@lists.osgeo.org</a><br class=""> > <a \
href="http://lists.osgeo.org/mailman/listinfo/qgis-user" \
class="">http://lists.osgeo.org/mailman/listinfo/qgis-user</a></p> \
</div></blockquote></div><br class=""></body></html>
_______________________________________________
Qgis-user mailing list
Qgis-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/qgis-user
[prev in list] [next in list] [prev in thread] [next in thread]
Configure |
About |
News |
Add a list |
Sponsored by KoreLogic