[Qgis-user] Re: Raster layer display control from Plugin

[JP Glutting]

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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