Ok, I figured this out. It was as simple as:
*resultsLayer.setContrastEnhancementAlgorithm(QgsContrastEnhancement.StretchToMinimumMaximum)*
That computes the min and max, and stretches the grayscale (to black
and white for boolean rasters).
In the mean time I was futzing around with:
* band = resultsLayer.bandNumber(resultsLayer.grayBandName()) *
* minVal = resultsLayer.minimumValue(band)*
* maxVal = resultsLayer.maximumValue(band)*
and
* resultsLayer.setMinimumValue(band, minVal, generateLookupTableFlag)*
* resultsLayer.setMaximumValue(band, maxVal,
generateLookupTableFlag)*
but it turns out that *resultsLayer.**setMaximumValue(band) *returns
the theoretical maximum (255) rather than the real maximum (1), which
is not what I wanted. You can get the correct value with
* maxVal = resultsLayer.bandStatistics(band).maximumValue*
However, it says that calling bandStatistics is very CPU intensive,
since it also calculates a lot of other stuff. As it turns out, the
StretchToMinimumMaximum algorithm seems to calculate the minmax
anyway, so none of that is needed.
My big mistake, as I was rushing through this, was to confuse extent
and values, as I was trying to copy from a tutorial and wasn't paying
close attention. Once I figured that out, it was easy.
On the other hand,
*resultsLayer.setColorShadingAlgorithm("PseudoColorShader")*
Doesn't seem to do anything at all. Strange.
Cheers,
JP
On Sat, Sep 4, 2010 at 6:35 PM, Benoit de Cabissole
<[email protected] <mailto:[email protected]>> wrote:
Hi JP,
I would suggest asking your question on the Qgis-developer list
instead of this one.
Below is what I've done to display a custom colormap on a raster.
Could it be adapted to your problem?
# Display the raster with the selected colour table:
#
# - tell the layer to use a QgsColorRampShader function
theLayer.setColorShadingAlgorithm(
QgsRasterLayer.ColorRampShader )
# - get a pointer to the raster shader function (QgsColorRampShader)
myColorRampShader =
theLayer.rasterShader().rasterShaderFunction()
# - set parameters for the QgsColorRampShader function
myColorRampShader.setColorRampType( QgsColorRampShader.DISCRETE )
myColorRampShader.setColorRampItemList( theTBL )
theLayer.setDrawingStyle( QgsRasterLayer.SingleBandPseudoColor )
# - refresh map & legend
if hasattr(theLayer, "setCacheImage"):
theLayer.setCacheImage( None )
theLayer.triggerRepaint()
self.iface.legendInterface().refreshLayerSymbology( theLayer )
# - tell QGIS that it needs to ask user to save changes
self.iface.mapCanvas().setDirty( True )
Cheers,
Benoit
-----Original Message-----
*From:* [email protected]
<mailto:[email protected]>
[mailto:[email protected]
<mailto:[email protected]>]*On Behalf Of *JP
Glutting
*Sent:* Saturday, 04 September 2010 17:47
*To:* [email protected] <mailto:[email protected]>
*Subject:* [Qgis-user] Re: Raster layer display control from
Plugin
No takers? No hints? I have been looking all over the place,
and I am stuck. If it is something absurdly simple, just point
me in the right direction.
Any ideas?
Thanks,
JP
On Fri, Sep 3, 2010 at 7:50 AM, JP Glutting
<[email protected] <mailto:[email protected]>> wrote:
Although here (http://blog.qgis.org/node/94) it seems to
indicate that SingleBandPseudoColor is a constant:
mypLayer->setColorRampingType(QgsRasterLayer::BLUE_GREEN_RED);
mypLayer->setDrawingStyle(QgsRasterLayer::SINGLE_BAND_PSEUDO_COLOR);
std::deque myLayerSet;
which is what I was thinking in the first place, and here
(
http://doc.qgis.org/stable/classQgsRasterLayer.html#36796f1a303dac9848ba3dce3e5527dc7b7c9814c053986846b579119d2e5be9
)
DrawingStyle is described as an enumerator, which seems
coherent. I am not sure how to do this from Python.
Cheers,
JP
On Fri, Sep 3, 2010 at 7:43 AM, JP Glutting
<[email protected] <mailto:[email protected]>> wrote:
Actually, I am not even sure that first part is the
way to do it. I tried this:
resultsLayer.setDrawingStyle(QtCore.QString('SingleBandPseudoColor'))
resultsLayer.setCacheImage(None)
resultsLayer.triggerRepaint()
(passing the 'SingleBandPseudoColor' style as a
string) and it makes the raster invisible. It still
shows up black in the Layers Panel, but it doesn't
show in the main window until you change the
properties manually (and it is Grayscale when you do).
It feels like I am pretty close, but I am not sure how
to interpret this code from the QGIS documentation:
myRasterLayer->setDrawingStyle
<http://classQgsRasterLayer.html#3a923f732bedd87d0b920c5552215434>(QgsRasterLayer::SingleBandPseudoColor
<http://classQgsRasterLayer.html#36796f1a303dac9848ba3dce3e5527dc7b7c9814c053986846b579119d2e5be9>);
(I never learned more than the basics of C++, and that
was a long time ago). The source code seems to
indicate that the format needs to be passed as a
string (of course, when the layer is generated):
00204QgsRasterLayer <http://classQgsRasterLayer.html>(int
dummy,
00205const QString& baseName = QString(),
00206const QString& path = QString(),
00207const QString& providerLib = QString(),
00208const QStringList& layers = QStringList(),
00209const QStringList& styles = QStringList(),
00210const QString& format = QString(),
00211 const QString & crs = QString() );
Thanks,
JP
On Fri, Sep 3, 2010 at 3:04 AM, JP Glutting
<[email protected] <mailto:[email protected]>>
wrote:
Hello,
I am working on a plugin (I mentioned it on the
list earlier, but it isn't relevant to the
question I have now). I have the results written
to a raster file, and I need to display it. I am
using this code:
resultsLayer =
qgis.core.QgsRasterLayer(self.query.results_file,
QtCore.QFileInfo(self.query.results_file).baseName())
qgis.core.QgsMapLayerRegistry.instance().addMapLayer(resultsLayer)
which works fine for opening the file, but I would
like to fine-tune the display so the user doesn't
have to reset the properties (in my test exaple
the values are 0 and 1 and the display is
essentially all black). I would like to either
display the results in pseudocolor directly, or in
grayscale with the scale stretched to the min and
max extent of the raster.
I tried the psuedocolor with this code:
resultsLayer.setDrawingStyle(qgis.core.QgsRasterLayer.SingleBandPseudoColor)
resultsLayer.setCacheImage(None)
resultsLayer.triggerRepaint()
which doesn't seem to do anything at all, and I am
just guessing, really.
I found a nice tutorial about how to calculate the
min and max extent of a raster and adjust the
display here:
http://linfiniti.com/2010/08/a-simple-qgis-python-tutorial/
and I tried the following code:
band =
resultsLayer.bandNumber(resultsLayer.grayBandName())
extentMin = 0.0
extentMax = 0.0
generateLookupTableFlag = False
extentMin, extentMax =
resultsLayer.computeMinimumMaximumFromLastExtent(band)
resultsLayer.setMinimumValue(band,
extentMin, generateLookupTableFlag)
resultsLayer.setMaximumValue(band,
extentMax, generateLookupTableFlag)
resultsLayer.setStandardDeviations(0.0)
resultsLayer.setUserDefinedGrayMinimumMaximum( True )
resultsLayer.setCacheImage(None)
resultsLayer.triggerRepaint()
but that fails with the following error:
Traceback (most recent call last):
File
"/Users//.qgis/python/plugins/mcelite/MCELiteDialog.py",
line 361, in accept
extentMin, extentMax =
resultsLayer.computeMinimumMaximumFromLastExtent(band)
TypeError: 'float' object is not iterable
and I don't understand what the float object is,
exactly.
Any help or suggestions much appreciated.
Cheers,
JP
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