<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="">Hi Stefan,<div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jul 31, 2015, at 9:37 AM, Stefan Kiefer <<a href="mailto:st_kiefer@web.de" class="">st_kiefer@web.de</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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Hi Nick,<br class="">
back to office I was eager to try by myself. Actually it seems that
the result of multiple AND or multiple layers - I didn't check this
by now - results in values slightly lower 1 (e.g. 0.9995 in my
case). And therefore maybe rounded to "0". What I have done is the
folowing:<br class="">
<br class=""></div></div></blockquote><div><br class=""></div><div><div>Thanks! I did try your suggestion and it provided me the results I was seeking of only showing the red routes:</div><div><br class=""></div><div>(1/("map@1" < 238 AND "map@1" > 210)) + (1/("map@2" < 123 AND "map@2" > 94)) + (1/("map@3" < 130 AND "map@3" > 98))</div><div><br class=""></div><div>Perhaps my math is fuzzy. Why would the divisor resolve this situation whereas multiplier in following has problems?</div><div><br class=""></div><div>((“m@1" < 238 AND “m@1" > 210) * 1) * ((“m@2" < 123 AND “m@2" > 94) * 1) * ((“m@3" < 130 AND “m@3" > 98) * 1)</div><div><br class=""></div></div>The floating point values is a why I believe we have a rounding bug in Raster Calculator. I suspect that during the calculation a number is converted to floating point, between 0 and 1 (eg 0.9995), and that causes the equation to result in all 0s. Its unusual that the calculator is performing floating point math because these are all integer values being operated on by value comparison operators and other integer numbers without any division which would cause floating point conversion or multiplication by a floating point. The numbers are all whole integers. I was hoping the original author could chime in on the tool and perhaps this is a bug.</div><div><br class=""></div><div>I’m on Mac OSX using 2.10.1 release and see same results on 2.8 release.</div><div><br class=""></div><div>I’m suspecting this may be a bug related to:</div><div><br class=""></div><div>Raster calculator always returns float32 tiffs</div><div><a href="https://hub.qgis.org/issues/10965" class="">https://hub.qgis.org/issues/10965</a></div><div>Raster calculator produces only 0 values with conditional expression</div><div><a href="https://hub.qgis.org/issues/11682" class="">https://hub.qgis.org/issues/11682</a></div><div><br class=""></div><div>There is this suggestion on the mailing list of how to resolve, however am a bit confused on the methods. The workaround may be to reproject the raster layer and I’m unsure why that’s required:</div><div><a href="http://lists.osgeo.org/pipermail/qgis-user/2014-November/029873.html" class="">http://lists.osgeo.org/pipermail/qgis-user/2014-November/029873.html</a></div><div><a href="http://lists.osgeo.org/pipermail/qgis-user/2014-November/029878.html" class="">http://lists.osgeo.org/pipermail/qgis-user/2014-November/029878.html</a></div><div><br class=""></div><div>Thanks again,</div><div>Nick</div><div><br class=""><blockquote type="cite" class=""><div class=""><div bgcolor="#FFFFFF" text="#000000" class="">
<meta name="qrichtext" content="1" class=""><div style="margin: 0px; text-indent: 0px;" class=""><!--StartFragment-->(1/("pm2-5-europe-2001-2010@1">240
AND
"pm2-5-europe-2001-2010@1"<250))*(1/("pm2-5-europe-2001-2010@2">139
AND "pm2-5-europe-2001-2010@2"<145)) *
(1/("pm2-5-europe-2001-2010@3">80 AND
"pm2-5-europe-2001-2010@3"<85))<br class="">
<br class="">
</div><div style="margin: 0px; text-indent: 0px;" class="">which
results in a perfektly fitting mask of my pseudo demand.<br class="">
</div><div style="margin: 0px; text-indent: 0px;" class="">Mayby you
could verfy this with your data<br class="">
</div><div style="margin: 0px; text-indent: 0px;" class=""><br class="">
cheers<br class="">
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Stefan<br class="">
<br class="">
<div class="moz-cite-prefix">Am 31.07.2015 um 08:48 schrieb Stefan
Kiefer:<br class="">
</div>
<blockquote cite="mid:1309030743.598358.1438325334696.JavaMail.open-xchange@omgreatgod.store" type="cite" class="">
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<div class="">
<div class="">Hi Nick,</div>
<div class="">you are absolutely right. My thought was, that you get A
layer with distinct values to identify the road. For a mask
you are on the right way, and I either don't understand the
behaviour except that you operate over three layers, which of
course should work.</div>
<div class="">Have you tryed to generate a composit of the three layers
and mask the single values resulting for road structures?
(it's more or less what I expected from my first approach.)</div>
<div class=""> </div>
<div class="">cheers</div>
<div class=""> </div>
<div class="">Stefan</div>
<br class="">
> Nick Papadonis <a class="moz-txt-link-rfc2396E" href="mailto:npapadonis@gmail.com"><npapadonis@gmail.com></a> hat am 31. Juli
2015 um 08:31 geschrieben:<br class="">
> <br class="">
> <br class="">
> Hi Stefan,<br class="">
> <br class="">
> It’s my understanding black has a value of 0 in the
resulting layer.<br class="">
> <br class="">
> I tried this and it results in similar image to step (a)
and also includes other colors at lower intensities mixed in
with the red. The red has the highest intensity in the
greyscale. I’m looking to create a binary image with just the
colors of red in the palette I choose and using this trace
vectors over the paths.<br class="">
> <br class="">
> Thanks,<br class="">
> Nick<br class="">
> <br class="">
> > On Jul 31, 2015, at 2:04 AM, Stefan Kiefer
<a class="moz-txt-link-rfc2396E" href="mailto:st_kiefer@web.de"><st_kiefer@web.de></a> wrote:<br class="">
> > <br class="">
> > Hi Nick,<br class="">
> > I believe it is black bcause you always get a value of
"1". Unfortunately I can not verify this, because I have no QGis
by this moment. Most propably you wanted to calculate:<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) *
((“m@1" < 238 AND “m@1" > 210) * "m@1") + ((“m@2" < 123
AND “m@2" > 94) * “m@2") + ((“m@3" < 130 AND “m@3" >
98) *“m@3"))<br class="">
> > <br class="">
> > cheers<br class="">
> > <br class="">
> > Stefan<br class="">
> > <br class="">
> > > Nick Papadonis <a class="moz-txt-link-rfc2396E" href="mailto:npapadonis@gmail.com"><npapadonis@gmail.com></a> hat
am 31. Juli 2015 um 07:49 geschrieben:<br class="">
> > > <br class="">
> > > <br class="">
> > > One more comment. The resulting layer histogram
is showing the pixel range spread over frequency in floating
point values. Is the raster calculator performing floating point
math with potential rounding error?<br class="">
> > > <br class="">
> > > I found it also interesting that the following
expression resulted in a layer, which when inspected for band
values, has integer values of 2 and 3. 3 being the value I want
for the red route.<br class="">
> > > <br class="">
> > > a) ((“m@1" < 238 AND “m@1" > 210) * 1) +
((“m@2" < 123 AND “m@2" > 94) * 1) + ((“m@3" < 130 AND
“m@3" > 98) * 1) <br class="">
> > > <br class="">
> > > I then change the expression to only use values 2
and greater and this shows properly:<br class="">
> > > b) ((“m@1" < 238 AND “m@1" > 210) * 1) +
((“m@2" < 123 AND “m@2" > 94) * 1) + ((“m@3" < 130 AND
“m@3" > 98) * 1) > 2<br class="">
> > > <br class="">
> > > I then changed the expression to ensure all three
values are obtained and it results in a black image of 0’s. I
was expecting only the red route to appear as it resulted in
value of 3 in step (a). <br class="">
> > > <br class="">
> > > ((“m@1" < 238 AND “m@1" > 210) * 1) +
((“m@2" < 123 AND “m@2" > 94) * 1) + ((“m@3" < 130 AND
“m@3" > 98) * 1) > 2.1<br class="">
> > > ((“m@1" < 238 AND “m@1" > 210) * 1) +
((“m@2" < 123 AND “m@2" > 94) * 1) + ((“m@3" < 130 AND
“m@3" > 98) * 1) >= 3<br class="">
> > > <br class="">
> > > I’m wondering how much testing the Raster
Calculator has gone through and if there is a possible bug here.
Perhaps something to do with floating point?<br class="">
> > > <br class="">
> > > Thanks again<br class="">
> > > <br class="">
> > > > On Jul 31, 2015, at 12:39 AM, Nick Papadonis
<a class="moz-txt-link-rfc2396E" href="mailto:npapadonis@gmail.com"><npapadonis@gmail.com></a> wrote:<br class="">
> > > > <br class="">
> > > > Folks,<br class="">
> > > > <br class="">
> > > > I’m using QGIS 10.1. The following
expressions result in a black raster of 0’s, when I expected
only red pixels to appears in the binary image indicating routes
on a map:<br class="">
> > > > <br class="">
> > > > a) (“m@1" < 238 AND “m@1" > 213 AND
“m@2" < 123 AND “m@2" > 98 AND “m@3" < 125 AND “m@3”
> 99) * 1<br class="">
> > > > b) ((“m@1" < 238 AND “m@1" > 210) * 1)
* ((“m@2" < 123 AND “m@2" > 94) * 1) * ((“m@3" < 130
AND “m@3" > 98) * 1)<br class="">
> > > > <br class="">
> > > > I then tried the following individual
expressions for each band as separate steps (sanity check) and
they work to cover the pixels in range:<br class="">
> > > > c) (“m@1" < 238 AND “m@1" > 213) * 1<br class="">
> > > > d) (“m@2" < 123 AND “m@2" > 98) * 1<br class="">
> > > > e) (“m@3" < 125 AND “m@3” > 99) * 1<br class="">
> > > > <br class="">
> > > > I then tried the following expression which
appears to create a proper greyscale image focusing on the red
pixels. I replaced the multiplication with addition to see what
was happening:<br class="">
> > > > f) ((“m@1" < 238 AND “m@1" > 210) * 1)
+ ((“m@2" < 123 AND “m@2" > 94) * 1) + ((“m@3" < 130
AND “m@3" > 98) * 1)<br class="">
> > > > <br class="">
> > > > The resulting raster has a Min = 0 and Max =
1.998. I was expecting it to be Min = 0 and Max = 3. The value
of 3 would indicate all 3 bands were positive on color match. I
then go to the layer properties and load calculate min/max again
and it is Min = 0 and Max = 3. I tried to change the min/max
settings on they layer and these settings will not stay set. The
layer goes back to Max = 1.998. What’s even more odd is the max
being a floating point number. I suspect that may be part of the
issue. Anyone know why this is the case for integer band values?
Has anyone successfully used the Raster Calculator to perform
this sort of work before?<br class="">
> > > > <br class="">
> > > > Thanks again,<br class="">
> > > > Nick<br class="">
> > > <br class="">
> > > _______________________________________________<br class="">
> > > Qgis-user mailing list<br class="">
> > > <a class="moz-txt-link-abbreviated" href="mailto:Qgis-user@lists.osgeo.org">Qgis-user@lists.osgeo.org</a><br class="">
> > > <a class="moz-txt-link-freetext" href="http://lists.osgeo.org/mailman/listinfo/qgis-user">http://lists.osgeo.org/mailman/listinfo/qgis-user</a><br class="">
> </div>
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