pyqgis: change transparency for cells with value 0

Question

I have a Raster file in which some cells have the value 0 and I would like to use pyqgis make them 100% transparent. I guess I have to use the QgsRasterTransparency class but I have no idea how.

I have a QgsRasterLayer object called rlayer and I can make a QgsRasterTransparency obejct, but I don't know how to apply the transparency on the rlayer object and how to define that the transparency only applies to those cells with value 0.

Answer 1

You can use following code for a single value as in your case.

rlayer = iface.activeLayer()

transparency  = rlayer.renderer().rasterTransparency()

pixel = QgsRasterTransparency.TransparentSingleValuePixel()

#setting value
pixel.min = 0
#setting transparency level
pixel.percentTransparent = 100

transparency.setTransparentSingleValuePixelList( [pixel] )

layer.triggerRepaint() 

However, for an interval of values it is preferable to use following code instead.

rlayer = iface.activeLayer()

transparency  = rlayer.renderer().rasterTransparency()

n = 2

pixels = [ QgsRasterTransparency.TransparentSingleValuePixel()
           for i in range(n) ]

min = [ min1, min2 ] # change min1, min2 for a numeric value
max = [ max1, max2 ] # change max1, max2 for a numeric value

trpcy = 100

for i, item in enumerate(pixels):
    item.min = min[i]
    item.max = max[i]
    item.percentTransparent = trpcy

transparency.setTransparentSingleValuePixelList( pixels )

layer.triggerRepaint()