[Qgis-user] Python script to iterate through attributes and then refresh the canvas - doesn't show any map....

[Frank van Baar]

Hi Joris,

 

Thanks for your suggestion - didn't realize atlas worked this way. It
however does not completely do what I want to do - the layer which it
changes the filter for also has specific formatting to highlight the region
etc. AND the OSM layer doesn't always display right. 

 

Any other suggestions anyone?


Frank

 

Van: Joris Hintjens [mailto:jorishin at gmail.com] 
Verzonden: 04 November 2014 11:27
Aan: Frank van Baar
CC: Qgis-user at lists.osgeo.org
Onderwerp: Re: [Qgis-user] Python script to iterate through attributes and
then refresh the canvas - doesn't show any map....

 

Why not use atlas generation in the print composer?

 Seems to me this corresponds with your "what i'm trying to achieve"

grts

Joris

 

 

Op 4-nov.-2014, om 09:14 heeft Frank van Baar <frank at van-baar.com> het
volgende geschreven:





Hi,

 

Am completely stuck with a QGIS project in Python and tried everything but
nothing seems to work. The python script does work as such BUT the canvas
never shows the map and therefor the exported maps are empty.. 

 

What I'm trying to achieve:

.       Create a Python script that iterates through a series of ca. 2500
polygons based on attribute value, zoom to layer extend and save the canvas
for each attribute as an image file.

.       I then use the image files in other documents

 

The issue is that while manually I get the canvas to reload and display the
map, this doesn't happen when running the python script. Have tried couple
of ways: 

1.      Don't load the project each time and just change the filter

2.      Add sleep timers to give the canvas time to refresh etc.

3.      Tried different QGIS versions (2.2, 2.4 & 2.6 on Win 64x)

 

But all to no avail.. Hope somebody's got a great idea how to solve it.

 

Regards,

Frank

 

Python code:

 

# File location & specifications 

PROJECTPATH = 'C:/Users/Frank/Documents /Targetting/Kaarten/'

PROJECTFILE = 'C:/Users/Frank/Documents
/Targetting/TargettingkaartV26qgs.qgs'

EXTSNAPSHOTS = '.jpg'

EXTSNAPSHOTS2 = '.png'

SUFFIX = '65Plus_v1'

last_id = 1

while last_id < 5:

        # Clear map canvas

        QgsMapLayerRegistry.instance().removeAllMapLayers()

        qgis.utils.iface.mapCanvas().refresh()

        

        # Open QGIS project

        QgsProject.instance().setFileName(PROJECTFILE)

        QgsProject.instance().read()

        qgis.utils.iface.mapCanvas().refresh()

        time.sleep(30)  

        canvas = qgis.utils.iface.mapCanvas()

        acl = canvas.layer(0)

        qgis.utils.iface.mapCanvas().layer(0).selectAll()

        selection = 'RijNo = ' + str(last_id) 

        

        acl.setSubsetString( selection )

        acl.triggerRepaint

        canvas.layer(1).triggerRepaint  

        time.sleep(5)   

        qgis.utils.iface.setActiveLayer(acl)

        # Zoom in and out to refresh potential issues with OpenLayer

        canvas.zoomByFactor(3)

        canvas.zoomByFactor(0.5)

        qgis.utils.iface.zoomToActiveLayer()

        qgis.utils.iface.mapCanvas().refresh()

        

        time.sleep(10)

        # Save project

        p=QgsProject.instance()

        p.setFileName(PROJECTFILE)

        p.write()

        # Save content of map canvas as image

        p = str(last_id) + 'kaart_' 

        qgis.utils.iface.mapCanvas().saveAsImage(PROJECTPATH+ p + SUFFIX +
EXTSNAPSHOTS)

        last_id = last_id +1

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