[Qgis-developer] Re: Raster layer display control from Plugin
JP Glutting
jpglutting at gmail.com
Sun Sep 5 10:52:25 EDT 2010
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 <benoit at exigesa.com>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:* qgis-user-bounces at lists.osgeo.org [mailto:
> qgis-user-bounces at lists.osgeo.org]*On Behalf Of *JP Glutting
> *Sent:* Saturday, 04 September 2010 17:47
> *To:* Qgis-user at lists.osgeo.org
> *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 <jpglutting at gmail.com> 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 <jpglutting at gmail.com> 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):
>>>
>>>
>>> 00204 QgsRasterLayer <http://classQgsRasterLayer.html>( int dummy,00205 const QString & baseName = QString(),00206 const QString & path = QString(),00207 const QString & providerLib = QString(),00208 const QStringList & layers = QStringList(),00209 const QStringList & styles = QStringList(),00210 const QString & format = QString(),
>>>
>>> 00211 const QString & crs = QString() );
>>>
>>> Thanks,
>>> JP
>>>
>>> On Fri, Sep 3, 2010 at 3:04 AM, JP Glutting <jpglutting at gmail.com>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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