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

[JP Glutting]

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<classQgsRasterLayer.html#3a923f732bedd87d0b920c5552215434>
(QgsRasterLayer::SingleBandPseudoColor<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 <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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