I am building a QGIS plugin that connects to a MySQL database in the local network, and then adds a subset of one of the tables to an in-memory layer; the subset is based on data currency (only taking the most recent observation for each location where measurements are made). This memory layer is successfully created.
However I then want to run some geoprocessing algorithms, and I'm having trouble using the in-memory layer in any of them.
self.stationuri = "point?crs=epsg:4326&field=id:integer&field={}:double&index=yes".format(self.cb_field.currentText())
self.vlayer = QgsVectorLayer(self.stationuri,"scratch","memory")
if not self.vlayer.isValid():
raise Exception("Failed to create in-memory layer")
self.vlayer.startEditing()
for i,r in enumerate(result): # Result is row-by-row result of SQL query
# Add features
...
self.vlayer.commitChanges()
self.vlayer.updateExtents()
# Add layer to map
QgsMapLayerRegistry.instance().addMapLayer(self.vlayer)
# Layer is successfully added to map with all features and geometry
# BELOW IS WHERE IT FALLS APART
try:
processing.runandload("gdalogr:gridinvdist",self.vlayer,self.cb_field.currentText(),2,0,0,0,0,0,0,0,'Float32',None) # None = in-memory output; I get the same error if I specify a string path and filename.
except Exception, e:
raise e
No exception is raised, but no output is produced or added to the TOC, but the following log is made in processing.log:
INFO|Mon May 04 2015 11:28:23|GDAL execution console output|/bin/sh: 1: /tmp/processing/bbebe7599c83446d9c2b03a251879657/OUTPUT.tif: not found|/bin/sh: 1: -zfield: not found||FAILURE: Source datasource is not specified.|Usage: gdal_grid [--help-general] [--formats]| [-ot {Byte/Int16/UInt16/UInt32/Int32/Float32/Float64/| CInt16/CInt32/CFloat32/CFloat64}]| [-of format] [-co "NAME=VALUE"]| [-zfield field_name] [-z_increase increase_value] [-z_multiply multiply_value]| [-a_srs srs_def] [-spat xmin ymin xmax ymax]| [-clipsrc <xmin ymin xmax ymax>|WKT|datasource|spat_extent]| [-clipsrcsql sql_statement] [-clipsrclayer layer]| [-clipsrcwhere expression]| [-l layername]* [-where expression] [-sql select_statement]| [-txe xmin xmax] [-tye ymin ymax] [-outsize xsize ysize]| [-a algorithm[:parameter1=value1]*] [-q]| <src_datasource> <dst_filename>||Available algorithms and parameters with their's defaults:| Inverse distance to a power (default)| invdist:power=2.0:smoothing=0.0:radius1=0.0:radius2=0.0:angle=0.0:max_points=0:min_points=0:nodata=0.0| Moving average| average:radius1=0.0:radius2=0.0:angle=0.0:min_points=0:nodata=0.0| Nearest neighbor| nearest:radius1=0.0:radius2=0.0:angle=0.0:nodata=0.0| Various data metrics| <metric name>:radius1=0.0:radius2=0.0:angle=0.0:min_points=0:nodata=0.0| possible metrics are:| minimum| maximum| range| count| average_distance| average_distance_pts|
The important part seems to be FAILURE: Source datasource is not specified. However self.vlayer.isValid() == True, so I don't see what is wrong with my input. I have tried substituting self.vlayer with 'memory:scratch' in the call to processing.runandload, but then I get the following error printed to the console (but not raised): Error: Wrong parameter value: memory:scratch.
I get the same issue when running this through the QGIS GUI, and using the dropdown menu to select my scratch layer which is in the TOC. This occurs whether I specify the output raster as in-memory or specify a location on disk.
This question seems similar, but their solution was to add the memory layer to the TOC before using it. I am already doing that and yet the error persists.
I thought that this was a general issue with memory layers and the QGIS geoprocessing algorithms, but the following works without issue:
processing.runandload("qgis:fixeddistancebuffer",self.vlayer, 500, 5, True, "output_buffer.shp")
What am I doing wrong? Why can't my memory source dataset "be specified" in some of the processing algorithms?
EDIT: here's the source code of gdalogr:gridinvdist if that's useful.
