Vjylku

I have used QGIS to batch import and visualise tiled elevation data. This is illuminated greyscale, with identical parameters used each time, so I would have expected the result to be seamless and the tile boundaries to be essentially invisible.

However, the result is a 'patchwork quilt' effect. The shading is not consistent from one tile to the next. I do not understand why not. This is the code used to apply the hillshading:

  def ShadeRaster(raster, pth):



    import processing   



    parameters = {'INPUT': "", 

      'BAND': 1, 

      'COMPUTE_EDGES': False,

      'ZEVENBERGEN': False,

      'Z_FACTOR': 1.0,

      'SCALE': 1.0,

      'AZIMUTH': 315,

      'COMBINED': False,

      'ALTITUDE': 45,

      'MULTIDIRECTIONAL': False,

      'OUTPUT': ""}



    parameters['INPUT'] =raster.name()

    parameters['OUTPUT'] = pth + '/' + raster.name() + '.tif'



    processing.runAndLoadResults('gdal:hillshade',parameters,feedback=feedback)

    return QgsProject.instance().mapLayersByName('Hillshade')[0]

As you can see, the elevation and azimuth of the light source are always the same. But this is how it looks:

Why?

OK... Got it. I changed approach a little bit, having realised that I don't have to run the Hillshade algorithm and generate a TIFF. I can just apply hillshade rendering to the memory raster layer.

I have now got a three stage process (repeated for each grid tile):

1. Create raster layer from xyz ASCII file


2. Set contrast enhancement to 'none'


3. Set render to 'hillshade'

Stages 2 and 3 can actually be done via the QGIS GUI quite easily and applied to multiple layers, but I have done it programmatically.

def ImportRaster(self, raster):



  from PyQt5.QtCore import QFileInfo



  fileInfo = QFileInfo(raster)

  path = fileInfo.filePath()

  baseName = fileInfo.baseName()



  layer = QgsRasterLayer(path, baseName)

  QgsProject.instance().addMapLayer(layer)



  return layer if layer.isValid() else None



def setNoEnhancement(self, layer): # set contrast enhancement to 'no enhancement'

  ContrastEnhancement = QgsContrastEnhancement.NoEnhancement

  myBand = layer.renderer().grayBand()

  myType = layer.renderer().dataType(myBand)

  myEnhancement = QgsContrastEnhancement(myType)

  myEnhancement.setContrastEnhancementAlgorithm(ContrastEnhancement, True)

  layer.renderer().setContrastEnhancement(myEnhancement)



def setRenderHillshade(self, layer): # set render type to 'hillshade'

  r = QgsHillshadeRenderer(layer.dataProvider(), 1, 315, 45)

  layer.setRenderer(r)



def XYZToShadedTIFF(self, fname):



  l = self.ImportRaster(fname) # import file, return layer 'l'



  if not l is None:

    self.setNoEnhancement(l) # ContrastEnhancement to 'none'

    self.setRenderHillshade(l) # hillshade

This works.

Thanks Michael for the assistance.