Nudge...

Is there anyone out there with knowledge of RasterLayer, MapLayerRegistry,
layerTreeRoot etc who can shed any light on the issues described below please?
Even just to know that there are no obvious errors or omissions in my approach
would be useful (so that I can direct my investigations elsewhere).

Many thanks,

Dan

-----Original Message-----
From: Qgis-user [mailto:qgis-user-boun...@lists.osgeo.org] On Behalf Of Hollis,
Dan
Sent: 19 October 2016 16:37
To: 'qgis-user@lists.osgeo.org'
Python

Hi,

I'm really hoping someone can help me with this.

I'm trying to write a Python script to batch process the loading of rasters
into QGIS. This script will be run in the Python Console. The rasters are
geotiffs created using some separate software that we have been developing. As
far as I can tell there are no problems with the rasters themselves i.e. I can
load and unload them using the standard buttons in the QGIS interface without
running into problems.

The rasters contain temperature data. There are two rasters for each day - one
containing actual values and one containing anomalies from the long-term
average. The aim is to load all of the data for one month such that there is a
full version of my script each group contains the two rasters for that day,
plus some vector layers overlaid on top (point temperature data, coastline
etc). I don't think the vector data are the cause of the problems I'm
encountering so I'm ignoring these in the rest of this posting.

I'm working on Windows 7. Until recently I was using QGIS 2.4 Chugiak. My
script worked well enough in that it would load all the layers as required and
the user could mostly interact with them without generating any errors i.e.
they could pan, zoom, identify, switch layers on/off, expand/contract groups.
However when the user tried to close down QGIS, or if they tried to remove the
layers prior to loading a different set of data, then the software would always
crash ("qgis-bin.exe has stopped working", "Crash dumped - minidump written to
C:" etc). This only happened when the layers had been loaded using my script.

The obvious conclusion was that there was something wrong / incomplete about
how my script loaded the layers. I've recently had QGIS 2.14 Essen installed so
I thought I'd take another look and see if I could work out what was wrong but
so far I've not had much success. The full version of my script now crashes
QGIS as the layers are loaded (a step backwards!). The strangest thing is that
it doesn't always fail in the same place - often it's while loading the layers
for the first group, but occasionally it loads up 2 or 3 groups before
crashing. There are no useful error messages or trace back to go on, only
"stopped working" and "minidump" messages. If I load only the vector layers
then it works, but as soon as I include the raster layers then things start
failing. I've added numerous print statements and done all sorts of refactoring
but to no avail.

I've now tried to come at this from a different angle - starting with the
simplest possible script and building it up until it fails. The code pasted
below shows where I've got to. The various functions reflect the structure of
my full script. I _think_ the problem must be something to do with the
functions - objects are possibly getting destroyed or corrupted as a result of
passing them around - but I just cannot work it out.

NB I started out with the simplest possible code i.e. no functions or loops of
any kind - just a sequential series of instructions. This works! I then
it also still worked. Finally I introduced add_groups() - it still loaded the
layers without crashing, but then I was back to the situation where QGIS would
crash when I remove the layers added by the script. This is different to my
full script (which crashes as the layers are loaded) despite one being a
simplified version of the other. I then reverted the last change (getting rid
of add_groups()) and it's crashing again i.e. what was working is no longer
working! Aaaaggghhh!!

If anyone can shed any light at all on this I would be very grateful. I have
spent many hours trying to unpick this without success. The most frustrating
thing is the lack of any useful error messages and the fact that the crashes
seem somewhat random (clearly connected with my script, but not entirely
reproducible).

Thanks,

Dan

import os

rlayer = QgsRasterLayer(layer_path, layer_name)

type = 'anomaly'

fn = '_'.join((date, short_name, type)) + '.tiff'
layer_path = os.path.join(data_folder, fn)
layer_name = ' '.join((short_name, type))

type = 'actual'

fn = '_'.join((date, short_name, type)) + '.tiff'
layer_path = os.path.join(data_folder, fn)
layer_name = ' '.join((short_name, type))

root = QgsProject.instance().layerTreeRoot()
for date in dates:
group_name = date + ' ' + short_name

data_folder = r'C:\path\to\my\data'
short_name = 'daily_mintemp'
dates = ['2016-08-01', '2016-08-02']

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