[Qgis-user] writing a new renderer in python

[Anita Graser]

Hello Sebastien,

Thank you for the useful source. This atleast explains the return value error. But I'm still facing the problem that attributeMap() doesn't return the attributes of the feature ...


-------- Original-Nachricht --------
> Datum: Fri, 21 Mar 2008 13:29:35 +0100
> Von: "Sebastien Vial" <sebastien.vial at gmail.com>
> An: "Anita Graser" <anitagraser at gmx.at>, qgis-user at lists.osgeo.org
> Betreff: Re: [Qgis-user] writing a new renderer in python

> Hello
> 
> I haven't read all your code
> but IMHO you should have a look to
> http://www.maths.lancs.ac.uk/~rowlings/Software/ratioRenderer/
> which is a python renderer build as a qgis plugin !
> 
> Seb
> 
> 2008/3/21, Anita Graser <anitagraser at gmx.at>:
> >
> > For my project I want to visualise speed on streets with a continuous
> > color renderer. I'd like it to show slow in red then change to yellow
> then
> > to green. Unfortunately QgsContinuousColorRenderer only allows to use
> two
> > colors. So I'm trying to write a new renderer inheriting
> QgsContinuousColor
> > Renderer.
> >
> > Is it possible to write a new renderer in python?
> >
> > I found some problems which I don't understand:
> >
> > 1.
> > I tried to rewirte the renderFeature function:
> > -------------------------------------------------------------
> > def renderFeature(self, painter, feature, image, scalefactor, selected,
> > widthScale=1):
> >      attrs = feature.attributeMap()
> >      fvalue = float(attrs[self.classificationField])
> > -------------------------------------------------------------
> > However, attributeMap() seems to always return a dictionary of length 1
> > allthough there should be 12 attributes. So I can't get a value for
> fvalue.
> >
> > 2.
> > If I catch the exception caused by problem 1 and set a default value the
> > function will continue to it's end. But then, I get a typeError:
> > TypeError: invalid result type from My3ColorRenderer.renderFeature()
> > I'm confused because I thought that this function returns void ...
> >
> > Anyone got an idea what I'm doing wrong?
> >
> > Thank you!
> >
> > My Code:
> >
> > -----------------------------------------------------------------
> >
> > from PyQt4.QtCore import *
> > from PyQt4.QtGui import *
> > from qgis.core import *
> > from qgis.gui import *
> >
> > class My3ColorRenderer(QgsContinuousColorRenderer):
> >     def __init__(self,vectorType):
> >         self.vectorType=vectorType
> >         QgsContinuousColorRenderer.__init__(self,vectorType)
> >
> >     def setMiddleSymbol(self,symbol):
> >         self.mMiddleSymbol=symbol
> >     def middleSymbol(self):
> >         return self.mMiddleSymbol
> >
> >     def name(self):
> >         return "FleetVis3ColorRenderer"
> >
> >     def symbols(self):
> >         list=[]
> >         list.append(self.mMinimumSymbol)
> >         list.append(self.mMiddleSymbol)
> >         list.append(self.mMaximumSymbol)
> >         return list
> >
> >     def setClassificationField(self,id):
> >         self.classificationField=id
> >
> >     def renderFeature(self, painter, feature, image, scalefactor,
> > selected, widthScale=1):
> >         #first find out the value for the classification attribute
> >         # ??? i dont know why it doesnt work ...
> >         attrs = feature.attributeMap()
> >         try:
> >             fvalue = float(attrs[self.classificationField])
> >         except:
> >             fvalue=50.0
> >
> >         minvalue = float(self.minimumSymbol().lowerValue())
> >         maxvalue = float(self.maximumSymbol().lowerValue())
> >         middlevalue = minvalue + maxvalue
> >         middlevalue=middlevalue/2
> >
> >         mincolor=QColor()
> >         maxcolor=QColor()
> >
> >         if self.vectorType == QGis.Line or self.vectorType ==
> QGis.Point:
> >             mincolor = self.minimumSymbol().pen().color()
> >             middlecolor=self.middleSymbol().pen().color()
> >             maxcolor = self.maximumSymbol().pen().color()
> >         else:#if polygon
> >             painter.setPen(self.minimumSymbol().pen())
> >             mincolor = self.minimumSymbol().fillColor()
> >             middlecolor=self.middleSymbol().fillColor()
> >             maxcolor = self.maximumSymbol().fillColor()
> >
> >         if (maxvalue - minvalue)!=0:
> >             if(fvalue<middlevalue):
> >                 red = int (middlecolor.red() * (fvalue - minvalue) /
> > (middlevalue - minvalue) + mincolor.red() * (middlevalue - fvalue) /
> > (middlevalue - minvalue))
> >                 green = int (middlecolor.green() * (fvalue - minvalue) /
> > (middlevalue - minvalue) + mincolor.green() * (middlevalue - fvalue) /
> > (middlevalue - minvalue))
> >                 blue =  int (middlecolor.blue() * (fvalue - minvalue) /
> > (middlevalue - minvalue) + mincolor.blue() * (middlevalue - fvalue) /
> > (middlevalue - minvalue))
> >             elif(fvalue==middlevalue):
> >                 red=int(middlecolor.red())
> >                 green=int(middlecolor.green())
> >                 blue=int(middlecolor.blue())
> >             else:
> >                 red = int (maxcolor.red() * (fvalue - middlevalue) /
> > (maxvalue - middlevalue) + middlecolor.red() * (maxvalue - fvalue) /
> > (maxvalue - middlevalue))
> >                 green = int (maxcolor.green() * (fvalue - middlevalue) /
> > (maxvalue - middlevalue) + middlecolor.green() * (maxvalue - fvalue) /
> > (maxvalue - middlevalue))
> >                 blue =  int (maxcolor.blue() * (fvalue - middlevalue) /
> > (maxvalue - middlevalue) + middlecolor.blue() * (maxvalue - fvalue) /
> > (maxvalue - middlevalue))
> >         else:
> >             red = int (mincolor.red())
> >             green = int (mincolor.green())
> >             blue = int (mincolor.blue())
> >
> >         if self.vectorType == QGis.Point:
> >             pen = self.minimumSymbol().pen()
> >             pen.setColor ( QColor(red, green, blue) )
> >             pen.setWidthF ( widthScale * pen.width() )
> >
> >             brush = self.minimumSymbol().brush()
> >
> >             brush.setColor ( QColor(red, green, blue) )
> >
> >             brush.setStyle ( Qt.SolidPattern )
> >
> >             img = QgsMarkerCatalogue.instance().imageMarker (
> > self.minimumSymbol().pointSymbolName(),
> self.minimumSymbol().pointSize(),pen,
> > brush)
> >
> >             if scalefactor:
> >                  scalefactor = 1
> >
> >         elif self.vectorType == QGis.Line:
> >             painter.setPen( QPen(QColor(red, green,
> blue),int(widthScale*
> > self.minimumSymbol().pen().width()) ))
> >
> >         else:
> >             painter.setBrush(QColor(red, green, blue))
> >             painter.setPen(Qt.NoPen)
> >
> >
> > --
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> > _______________________________________________
> > Qgis-user mailing list
> > Qgis-user at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/qgis-user
> >
> 
> 
> 
> -- 
> Sébastien VIAL
> Prof d'Info - Resp. TIC/Comm - Formateur SIG
> Lycée Agricole du Balcon des Ardennes
> http://www.lebalcon.fr
> tel : 03-24-57-66-71

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