4

I'm trying to update a single band pseudo color renderer with new min/max values from the python console. All the code samples i have been able to find deal with constructing a renderer from scratch, but in this case I have a color ramp setup for an existing layer and I want to be able to stretch to color ramp with new min/max values.

I can set the new min/max values for the renderer, I just haven't figured out how to reclassify the color ramp (I'm looking for the equivalent of hitting the "classify" button in the style properties dialog).

This is what I have so far:

l = iface.activeLayer()

provider = l.dataProvider()
extent = canvas.extent()
stats = provider.bandStatistics(1, QgsRasterBandStats.All, extent)

min = stats.minimumValue
max = stats.maximumValue

l.renderer().setClassificationMin(min)
l.renderer().setClassificationMax(max)
4

With the next code you can get a ramp color red-yellow-blue . The min/max values for the renderer are got from raster stats.

from PyQt4.QtCore import *
from PyQt4.QtGui import *

layer = iface.activeLayer()

renderer = layer.renderer()
provider = layer.dataProvider()
extent = layer.extent()

ver = provider.hasStatistics(1, QgsRasterBandStats.All)

stats = provider.bandStatistics(1, QgsRasterBandStats.All,extent, 0)

if ver is not False:
    print "minimumValue = ", stats.minimumValue

    print "maximumValue = ", stats.maximumValue

if (stats.minimumValue < 0):
    min = 0  

else: 
    min= stats.minimumValue

max = stats.maximumValue
range = max - min
add = range//2
interval = min + add

colDic = {'red':'#ff0000', 'yellow':'#ffff00','blue':'#0000ff'}

valueList =[min, interval, max]

lst = [ QgsColorRampShader.ColorRampItem(valueList[0], QColor(colDic['red'])), 
        QgsColorRampShader.ColorRampItem(valueList[1], QColor(colDic['yellow'])), 
        QgsColorRampShader.ColorRampItem(valueList[2], QColor(colDic['blue']))]

myRasterShader = QgsRasterShader()
myColorRamp = QgsColorRampShader()

myColorRamp.setColorRampItemList(lst)
myColorRamp.setColorRampType(QgsColorRampShader.INTERPOLATED)
myRasterShader.setRasterShaderFunction(myColorRamp)

myPseudoRenderer = QgsSingleBandPseudoColorRenderer(layer.dataProvider(), 
                                                    layer.type(),  
                                                    myRasterShader)

layer.setRenderer(myPseudoRenderer)

layer.triggerRepaint()

Before running the code (raster in Map Canvas must be the active layer):

enter image description here

After running the code at the Python Console of QGIS:

enter image description here

  • Thanks for the reply but this doesn't help me. As I tried to explain in the question I already have a raster layer loaded and symbolized. I don't want to define the color ramp because I want to be able to use this to stretch any raster layer I have loaded with whatever color ramp I already have set. I just want to reclassify the existing color ramp to the new min/max values. – amcaninch May 28 '15 at 22:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.