[GIS] Auto-Update Color-Ramp to Current Display Extent

color rampdisplayqgis

When displaying raster files in Qgis with the color-ramp stretched to the min/max values of the current display extent, the min/max values don't update automatically when zooming or panning to a new area.

The only way i know around it is to manually recalculate the values each time, which can be quite a pain.

I know this functionality to be a basic feature in ArcMap, so maybe I'm just missing something in the display options. So if anyone knows how to get the min/max extent to auto-update, please let me know how to do it.
Thanks!

BTW: I'm currently using Qgis 2.4.0, but I encountered the same issue in all earlier versions I worked with.

Best Answer

Yes what you say is correct, but a plugin called "Raster" can help you a little bit. But this works only on grey scale.

Related Solutions

[GIS] How to update raster color ramp with new min/max values using PyQGIS

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

Best Answer

Related Solutions

[GIS] How to update raster color ramp with new min/max values using PyQGIS

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