[processing]added new example script (contributed by Michael Douchin)

python/plugins/processing/script/scripts/Create_rasters_from_canvas_for_each_vector_layer_feature_extent.py

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+##[Example scripts]=group
+##Create rasters from canvas for each vector feature extent=name
+##vector_layer=vector
+##scale=number 250000.0
+##dpi=number 96
+##image_width_mm=number 0
+##image_height_mm=number 0
+##output_directory=folder
+##outputDir=output string
+
+from qgis.core import *
+from qgis.gui import *
+from qgis.utils import iface
+from PyQt4.QtCore import *
+from PyQt4.QtGui import *
+import os
+
+# Loop though grid layerfeatures
+layer = processing.getObject(vector_layer)
+provider = layer.dataProvider()
+
+# Get map renderer
+mapRenderer = iface.mapCanvas().mapRenderer()
+
+# Create a new composition
+c = QgsComposition(mapRenderer)
+c.setPrintResolution(dpi)
+
+# Add a composer map object
+x, y = 0, 0
+composerMap = QgsComposerMap(c, x, y, image_width_mm, image_height_mm)
+c.addComposerMap(composerMap)
+composerMap.setBackgroundEnabled(False)
+
+# World file
+c.setWorldFileMap(composerMap)
+c.setGenerateWorldFile( True )
+
+# Get vector layer features
+feats = processing.features(layer)
+nFeat = len(feats)
+i = 0
+progress.setText(u'%s tiles to be generated' % nFeat)
+
+# Iterate over the features
+for feat in feats:
+    # Log progression
+    progress.setPercentage(int(100 * i / nFeat))
+    i+=1
+
+    # Get the feature bouding box
+    geom = feat.geometry()
+    rect = geom.boundingBox()
+
+    # Recalculate paper width and heigh if not given
+    if not image_width_mm and scale > 0:
+        image_width_mm = rect.width() * 1000 / scale
+    if not image_height_mm and scale > 0:
+        image_height_mm = rect.height() * 1000 / scale
+
+    # Calculate image size in Pixel
+    inch2mm = 25.4
+    image_width_pixel = int(image_width_mm * dpi / inch2mm)
+    image_height_pixel = int(image_height_mm * dpi / inch2mm)
+    progress.setText(u'Feature %s - Image width : %s * %s mm / %s * %s pixels' % (
+            i,
+            image_width_mm,
+            image_height_mm,
+            image_width_pixel,
+            image_height_pixel
+        )
+    )
+
+    # Set paper and composerMap width and height
+    c.setPaperSize(image_width_mm, image_height_mm)
+    composerMap.setItemPosition(x, y, image_width_mm, image_height_mm)
+
+    # Set the map extent and scale
+    composerMap.setNewExtent(rect)
+    if scale > 0:
+        composerMap.setNewScale(scale)
+
+    # Image destination path
+    outputPath= "tile_%s_%s" % (scale, i)
+    outputImagePath = os.path.join(output_directory, outputPath + '.png')
+
+    # Generate image from composition
+    myImage = c.printPageAsRaster(0)
+    myImage.save(outputImagePath)
+
+    # Generate World file
+    wf = c.computeWorldFileParameters()
+    outputWorldPath = os.path.join(output_directory, outputPath + '.pgw')
+    with open(outputWorldPath, 'w') as f:
+        f.write('%s\n' % wf[0])
+        f.write('%s\n' % wf[1])
+        f.write('%s\n' % wf[3])
+        f.write('%s\n' % wf[4])
+        f.write('%s\n' % wf[2])
+        f.write('%s\n' % wf[5])
+
+# export chosen output directory as a output variable
+outputDir = output_directory

python/plugins/processing/script/scripts/Create_rasters_from_canvas_for_each_vector_layer_feature_extent.py.help

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+(dp0
+S'outputDir'
+p1
+VThe directory where the rasters will be saved. This output can be used as a parameter for another script or algorithm (for example upcoming gdalbuildvrt )
+p2
+sS'ALG_DESC'
+p3
+VBuilding a good looking map often implies to create a QGIS project with many layers : roads, styled dem, contour lines, rivers, etc.\u000aFor large areas, QGIS can suffer to render each layers every time the user pan or zoom in or out. \u000a\u000aThis algorithm allows to create a georeferenced raster which mimics the image rendered by QGIS for all displayed layers. This way you can use the exported raster instead of all the layers as a base layer for your projects.\u000a\u000aThe user chooses the input vector layer, a scale and optionnaly the size of the raster in mm. The script iterate over the vector features. \u000a\u000aFor each feature:\u000a\u000a* the extent of the feature is calculated\u000a* the size of the output raster is calculated in mm "paper size", unless width and height are given\u000a* the canvas is rendered for the feature extent, at the given scale, and the result is saved as a png\u000a* a world file containing the georeferencement parameters is also saved ( *.pgw  )
+p4
+sS'image_height_mm'
+p5
+V(optionnal) The height in mm of the output raster. If left to 0, the script will calculate it automatically to render the whole feature extent.
+p6
+sS'ALG_CREATOR'
+p7
+VMicha�l DOUCHIN ( 3liz.com ) 
+p8
+sS'vector_layer'
+p9
+VThe vector layer containing the features to use to calculate each raster extent. You can use an existing layer, or a layer created with other algorithm (for example a regular grid of 250km by 250km)
+p10
+sS'output_directory'
+p11
+VThe directory where the rasters will be saved.
+p12
+sS'scale'
+p13
+VThe scale at which the canvas will be rendered
+p14
+sS'ALG_HELP_CREATOR'
+p15
+VMicha�l DOUCHIN ( 3liz.com ) 
+p16
+sS'image_width_mm'
+p17
+V(optionnal) The width in mm of the output raster. If left to 0, the script will calculate it automatically to render the whole feature extent.
+p18
+sS'dpi'
+p19
+VThe resolution of the output rasters. "dpi" means "dot per inch"
+p20
+s.