[GIS] Extent problem in PyQgis

pyqgispythonqgis-2.10qgis-2.11

I'm trying to set the extent of a square feature to the canvas, that works in QGIS, but when I print the canvas into a PDF, it always gives me some empty area, below is the screenshot of QGIS canvas having feature extent:

and below is the resulting PDF having empty spaces:

the pyqgis code used to get these results:

from qgis.core import *  

mr=iface.mapCanvas().mapRenderer()  
composition = QgsComposition(mr)
composition.setPaperSize(220, 220)
composerMap=QgsComposerMap(composition,0,0,composition.paperWidth(),composition.paperHeight())
composition.addItem(composerMap)

layer =  QgsVectorLayer('Polygon?crs=EPSG:4326', 'poly' , "memory")
pr = layer.dataProvider() 
poly = QgsFeature()
poly.setGeometry(QgsGeometry.fromWkt("POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))"))
pr.addFeatures([poly])
layer.updateExtents()
QgsMapLayerRegistry.instance().addMapLayers([layer])
bb =  poly.geometry().boundingBox()
iface.mapCanvas().setExtent(bb)
iface.mapCanvas().refresh()
composition.refreshItems()
composition.exportAsPDF('test.pdf')

Best Answer

The following code should work:

from qgis.core import *

# create an in-memory layer and add it to the QGIS project
layer =  QgsVectorLayer('Polygon?crs=EPSG:4326', 'poly' , "memory")
pr = layer.dataProvider() 
poly = QgsFeature()
poly.setGeometry(QgsGeometry.fromWkt("POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))"))
pr.addFeatures([poly])
layer.updateExtents()
QgsMapLayerRegistry.instance().addMapLayers([layer])

# set map canvas extent
bb =  poly.geometry().boundingBox()
iface.mapCanvas().setExtent(bb)

mr = iface.mapCanvas().mapRenderer()
composition = QgsComposition(mr)
composition.setPaperSize(220, 220)
composition.setPlotStyle(QgsComposition.Print)
composerMap = QgsComposerMap(
    composition, 0, 0, 
    composition.paperWidth(), composition.paperHeight()
)
composerMap.zoomToExtent(bb)
composition.addItem(composerMap)
composition.exportAsPDF('test.pdf')

There are 2 main differences:

In your code, the layer was not included in the map composer. One way for solving this is to create the layer before creating the map composer. Obviously you could manage this part somehow otherwise you would not have anything in your PDF.
You need to set the extent of the composer map manually to fit the rectangle with composerMap.zoomToExtent(bb).

The resulting PDF is as follows:

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[GIS] Problem loading vector layer (pyQGIS)

I had similar issue.

Found that the problem could be due to the following possibilities:

When you set up the QgsApplication, the PrefixPath must be done correctly.

My QGIS was installed on /usr/share/qgis.

But somehow I need to set the PrefixPath as "/usr" & not "/usr/share/qgis":
```
QgsApplication.setPrefixPath("/usr", True)
```

The path of the .shp files.

Assuming they are under a sub-directory from current path, "Maps/", you can load the file with:

mapFile = "Maps/world_borders.shp"
layer = QgsVectorLayer(os.path.abspath(mapFileName), mapFileName[mapFileName.rfind("/")+1:-4], "ogr")

Lastly, not all .shp files are created 'equal'. ;P

Some .shp file can be loaded without problem into QGIS & displayed.

Some, probably created in ESRI ArcMap, require the rest of the files (.shp, .shx, .dbf, .prj, .sbn, .sbx)

Hope this info help.

[GIS] QgsMapRenderer to export current extent using PyQGIS

Don't know if this is just a typo in your post, but if not, this could cause a blank image..

# set layer set
layers = qgis.utils.iface.legendInterface.layers()

This should actually be qgis.utils.iface.legendInterface().layers() (note that legendInterface must be the method call, done by adding braces() )

lst = []
for layer in layers:
    lst.append(layer.())

What you want to do, is to add each layers id by appending layer.id()
Hope that helps!

Edit:
Did you try to save a layer with scale-based visibility enabled? Cause the renderer scales the image to full-extend prior to saving - maybe your layer data is invisible at that zoom-level?!

Btw. this is the code that worked for me (or at least with the vector-, shape-, and raster layers I tested it with ;) )

PS. When using rect = QgsRectangle(renderer.extent()) instead of renderer.fullExtent() the image I get is blank, too.

    imageType = "png"
    pathToFile = "/Users/%u/Desktop/"

    # create image
    img = QImage(QSize(800,600), QImage.Format_ARGB32_Premultiplied)

    # set image's background color
    color = QColor(255,255,255)
    img.fill(color.rgb())

    # create painter
    p = QPainter()
    p.begin(img)
    p.setRenderHint(QPainter.Antialiasing)

    renderer = QgsMapRenderer()
    # set layer set
    lst = []


    layers = iface.legendInterface().layers()
    for layer in layers:
        lst.append(layer.id())

    renderer.setLayerSet(lst)
    print "Set rendered"

    # set extent
    rect = QgsRectangle(renderer.fullExtent())
    rect.scale(1.1)
    renderer.setExtent(rect)

    # set output size
    renderer.setOutputSize(img.size(), img.logicalDpiX())

    print "Prepared to render"

    # do the rendering
    renderer.render(p)

    print "rendered"
    p.end()
    print "painter ended"
    # save image
    img.save(pathToFile + self.activeLayer.name() + "." + imageType ,imageType)

Best Answer

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