Re: [Qgis-developer] Cleanly create memory layer in Python?
Hi Chris On Mon, Jan 17, 2011 at 10:00 PM, Chris Crook ccr...@linz.govt.nz wrote: I've added submitted a patch to implement this change at http://trac.osgeo.org/qgis/ticket/3414. Changes made are: * QgsCoordinateReferenceSystem? string constructor has been generalised to allow string formats epsg:1234 postgis:1234 internal:1234 proj4:proj_4_string wkt:wkt_string wkt_string This is implemented by a createFromString function, similar to the createFromId function Looks good! * Changed QgsMemoryProvider URI format to: memory?geometry=Pointindex=yescrs=epsg:1234field=id:integerfield=name:string(25) I would probably prefer to have uri point? instead of memory?geometry=point... since the fact that we are using memory provider is given as another parameter to the vector layer constructor, so in future we would save some typing ;-) The URI can contain the following items: geometry=Point|LineString|Polygon|MultiPoint|MultiLineString|MultiPolygon index=yes - creates a spatial index crs=... - defines the CRS in one of the formats above field=definition - defines an attribute field. The field definition is a field name, optionally followed by :type(length,precision), where type is one of integer, int, real, double, and string (int/integer are synonyms, as are real/double). Eg field=magnitude:real(16,2) field=owner:string(64) field=owner This uses Qurl for encoding and decoding the strings. To provide backwards compatibility, if there is no geometry query string field, then the path is taken as the geometry type. For example point point?crs=epsg:1234 Good. * Added an option crs= to the QgsDelimitedTextProvider URI, so that plugin code can specify the CRS when creating a delimited text layer. The crs can be any of the formats listed above. Also updated the provider to use Qurl for encoding and decoding the URI, to ensure consistent handling of special characters. * Made a couple of small fixes to the QgsMemoryProviderPlugin UI component to ensure that it correctly remembers the last choice of delimiter type (and to encode the data source URI using Qurl) Then it would be also great to have the possibility to set CRS in the GUI... One thing I haven't done is to modify the handling of datasourceUri in QgsVectorLayer to ensure that it always uses the datasourceUri from the provider, rather than storing its own version when the layer is created (or the provider is reset). I'm not sure how safe this would be - that is whether all the data providers correctly handle the datasourceUri() function. I think this would be the right thing to do though - I think that the provider should be responsible for its own URI. Any comments on the wisdom of changing this would be welcome! Currently I don't really like this idea. It's not usual that data source URI would change inside the provider, so I would be happy to keep the current situation. Developers can be advised to use the new syntax (after all it's less verbose) and we have no problems. Regards Martin ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
RE: [Qgis-developer] Cleanly create memory layer in Python?
Hi Martin On the choice of memory?geometry=point... Vs point?.., at the moment both are supported. I guess I lean towards the memory?geometry=... because I think it better follows the natural understanding of a url, in that the path defines the location, and the query string defines attributes. That said, memory is perhaps more properly the authority part of a URL (ie memory://?geometry=point)! One other point in favour of encoding the geometry type in the query string is that (in principle) the path component of the Url could be tampered with by the code for handling absolute/relative paths when the project is saved/reloaded, whereas the query string should not be. I'm not strongly attached to either alternative. On using the provider datasourceUri() rather than caching this in QgsVectorLayer(). It seems to me more logical that the provider owns the Uri by which it can be recreated, and which it understands. The QgsVectorLayer has no understanding of the Uri - it just passes it through to the provider, so why should it assume it will not change. In terms of the memory layer URI, even if the layer was set up with the new Uri format, including fields etc, it will not include fields a user may have added or removed manually after creating the layer. On setting the delimited text CRS in the plugin user interface. I chose not to mainly out of laziness/other priorities! Of course the CRS can still be set through the interface, at least for the layer (rather than the provider). It remains an option for future implementation :-) Cheers Chris -Original Message- From: Martin Dobias [mailto:wonder...@gmail.com] Sent: Thursday, 20 January 2011 8:51 a.m. To: Chris Crook Cc: qgis-developer@lists.osgeo.org Subject: Re: [Qgis-developer] Cleanly create memory layer in Python? Hi Chris On Mon, Jan 17, 2011 at 10:00 PM, Chris Crook ccr...@linz.govt.nz wrote: I've added submitted a patch to implement this change at http://trac.osgeo.org/qgis/ticket/3414. Changes made are: * QgsCoordinateReferenceSystem? string constructor has been generalised to allow string formats epsg:1234 postgis:1234 internal:1234 proj4:proj_4_string wkt:wkt_string wkt_string This is implemented by a createFromString function, similar to the createFromId function Looks good! * Changed QgsMemoryProvider URI format to: memory?geometry=Pointindex=yescrs=epsg:1234field=id:integerfield=n ame:string(25) I would probably prefer to have uri point? instead of memory?geometry=point... since the fact that we are using memory provider is given as another parameter to the vector layer constructor, so in future we would save some typing ;-) The URI can contain the following items: geometry=Point|LineString|Polygon|MultiPoint|MultiLineString|MultiPoly gon index=yes - creates a spatial index crs=... - defines the CRS in one of the formats above field=definition - defines an attribute field. The field definition is a field name, optionally followed by :type(length,precision), where type is one of integer, int, real, double, and string (int/integer are synonyms, as are real/double). Eg field=magnitude:real(16,2) field=owner:string(64) field=owner This uses Qurl for encoding and decoding the strings. To provide backwards compatibility, if there is no geometry query string field, then the path is taken as the geometry type. For example point point?crs=epsg:1234 Good. * Added an option crs= to the QgsDelimitedTextProvider URI, so that plugin code can specify the CRS when creating a delimited text layer. The crs can be any of the formats listed above. Also updated the provider to use Qurl for encoding and decoding the URI, to ensure consistent handling of special characters. * Made a couple of small fixes to the QgsMemoryProviderPlugin UI component to ensure that it correctly remembers the last choice of delimiter type (and to encode the data source URI using Qurl) Then it would be also great to have the possibility to set CRS in the GUI... One thing I haven't done is to modify the handling of datasourceUri in QgsVectorLayer to ensure that it always uses the datasourceUri from the provider, rather than storing its own version when the layer is created (or the provider is reset). I'm not sure how safe this would be - that is whether all the data providers correctly handle the datasourceUri() function. I think this would be the right thing to do though - I think that the provider should be responsible for its own URI. Any comments on the wisdom of changing this would be welcome! Currently I don't really like this idea. It's not usual that data source URI would change inside the provider, so I would be happy to keep the current situation. Developers can be advised to use the new syntax (after all it's less verbose) and we have no problems. Regards Martin
RE: [Qgis-developer] Cleanly create memory layer in Python?
I've added submitted a patch to implement this change at http://trac.osgeo.org/qgis/ticket/3414. Changes made are: * QgsCoordinateReferenceSystem? string constructor has been generalised to allow string formats epsg:1234 postgis:1234 internal:1234 proj4:proj_4_string wkt:wkt_string wkt_string This is implemented by a createFromString function, similar to the createFromId function * Changed QgsMemoryProvider URI format to: memory?geometry=Pointindex=yescrs=epsg:1234field=id:integerfield=name:string(25) The URI can contain the following items: geometry=Point|LineString|Polygon|MultiPoint|MultiLineString|MultiPolygon index=yes - creates a spatial index crs=...- defines the CRS in one of the formats above field=definition - defines an attribute field. The field definition is a field name, optionally followed by :type(length,precision), where type is one of integer, int, real, double, and string (int/integer are synonyms, as are real/double). Eg field=magnitude:real(16,2) field=owner:string(64) field=owner This uses Qurl for encoding and decoding the strings. To provide backwards compatibility, if there is no geometry query string field, then the path is taken as the geometry type. For example point point?crs=epsg:1234 * Added an option crs= to the QgsDelimitedTextProvider URI, so that plugin code can specify the CRS when creating a delimited text layer. The crs can be any of the formats listed above. Also updated the provider to use Qurl for encoding and decoding the URI, to ensure consistent handling of special characters. * Made a couple of small fixes to the QgsMemoryProviderPlugin UI component to ensure that it correctly remembers the last choice of delimiter type (and to encode the data source URI using Qurl) One thing I haven't done is to modify the handling of datasourceUri in QgsVectorLayer to ensure that it always uses the datasourceUri from the provider, rather than storing its own version when the layer is created (or the provider is reset). I'm not sure how safe this would be - that is whether all the data providers correctly handle the datasourceUri() function. I think this would be the right thing to do though - I think that the provider should be responsible for its own URI. Any comments on the wisdom of changing this would be welcome! Cheers Chris -Original Message- From: Martin Dobias [mailto:wonder...@gmail.com] Sent: Saturday, 8 January 2011 7:06 a.m. To: Chris Crook Cc: qgis-developer@lists.osgeo.org Subject: Re: [Qgis-developer] Cleanly create memory layer in Python? On Thu, Jan 6, 2011 at 9:16 PM, Chris Crook ccr...@linz.govt.nz wrote: Hi All I'm wanting to create a memory provider in Python without invoking the CRS selection dialog (even if the QGIS settings are set to Prompt for CRS when a new layer is created. At the moment my code looks like: settings = QSettings() prjSetting = settings.value(/Projections/defaultBehaviour) settings.setValue(/Projections/defaultBehaviour, QVariant()) layer = QgsVectorLayer(point,name,memory) if prjSetting: settings.setValue(/Projections/defaultBehaviour,prjSetting) This does work, but it seems a bit cumbersome (at first glance it doesn't even look like creating a vector layer!), so I'm wondering if there is a cleaner approach.. Hi Chris I agree this is cumbersome. A possible solution would be to extend the URI for memory provider - currently it accepts only a string with geometry type. New syntax could be introduced that would explicitly set layer CRS, e.g. geometry=pointcrs=4326. Any thoughts and patches are welcome. Regards Martin __ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or i...@linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank you. __ ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
RE: [Qgis-developer] Cleanly create memory layer in Python?
Hi Martin and list readers I'm experimenting with using a Url format very similar to what Martin suggested. I'm thinking that this could include the Crs, the list of fields, and the creation of a spatial index. I'm thinking that a Url of the form: memory?geometry=pointcrs=1234index=yesfield=integer:idfield=string:name ... The crs can be a simple srid, epsg:id, or (possibly) a proj4 text string. The path component of this is redundant of course - it could be anything. To retain backward compatibility though if there is no geometry query field, then the query path will be used. So the format could be point?crs=1234index=yes... Including the index in the URI is useful for me (for the MemoryLayerSaver plugin), as it restores that when the layer is recreated when a project is reopened. I'm not so sure about whether to include the field definitions. And if I do, I'm not sure about the best way to encode them, and whether to include length and precision fields. It would probably be more conventional to use something like name:type:length:precision for each field? Any thoughts. Finally, I'd like to override the dataSourceUri() function to return a definition reflecting the current state of the provider (ie index, fields, etc). This is potentially breaking to plugin code if it uses this to determine the geometry type, not that there is any reason to do so. Cheers Chris -Original Message- From: Martin Dobias [mailto:wonder...@gmail.com] Sent: Saturday, 8 January 2011 7:06 a.m. To: Chris Crook Cc: qgis-developer@lists.osgeo.org Subject: Re: [Qgis-developer] Cleanly create memory layer in Python? On Thu, Jan 6, 2011 at 9:16 PM, Chris Crook ccr...@linz.govt.nz wrote: Hi All I'm wanting to create a memory provider in Python without invoking the CRS selection dialog (even if the QGIS settings are set to Prompt for CRS when a new layer is created. At the moment my code looks like: settings = QSettings() prjSetting = settings.value(/Projections/defaultBehaviour) settings.setValue(/Projections/defaultBehaviour, QVariant()) layer = QgsVectorLayer(point,name,memory) if prjSetting: settings.setValue(/Projections/defaultBehaviour,prjSetting) This does work, but it seems a bit cumbersome (at first glance it doesn't even look like creating a vector layer!), so I'm wondering if there is a cleaner approach.. Hi Chris I agree this is cumbersome. A possible solution would be to extend the URI for memory provider - currently it accepts only a string with geometry type. New syntax could be introduced that would explicitly set layer CRS, e.g. geometry=pointcrs=4326. Any thoughts and patches are welcome. Regards Martin __ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or i...@linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank you. __ ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
RE: [Qgis-developer] Cleanly create memory layer in Python?
Looks like one of my ideas below won't work. I was hoping that I could over-ride the QgsDataProvider.dataSourceUri() function to update the Uri as the provider was modified (such as adding an index). However I think that this function is only referenced when the provider is set up (ie QgsVectorLayer.setDataProvider() and QgsVectorLayer.setSubString()), which means any other provider initiated changes don't get reflected back to the QgsVectorLayer :-( For some providers (osm, postgres) the dataSourceUri() function is used to reset the data source when the provider is first assigned to the layer, but not thereafter. I'm wondering why the QgsDataProvider.dataSourceUri() function isn't used whenever the Uri is needed - as it seems to me it belongs very much to the provider and not to the layer? Would it make sense to replace references to QgsMapLayer.mDataSource with calls to QgsMapLayer.dataSourceUri(), and to have that use the provider dataSourceUri() function unless the provider was not defined. Cheers Chris -Original Message- From: Chris Crook Sent: Monday, 10 January 2011 8:51 a.m. To: 'Martin Dobias' Cc: qgis-developer@lists.osgeo.org Subject: RE: [Qgis-developer] Cleanly create memory layer in Python? Hi Martin and list readers I'm experimenting with using a Url format very similar to what Martin suggested. I'm thinking that this could include the Crs, the list of fields, and the creation of a spatial index. I'm thinking that a Url of the form: memory?geometry=pointcrs=1234index=yesfield=integer:idfield=string:name ... The crs can be a simple srid, epsg:id, or (possibly) a proj4 text string. The path component of this is redundant of course - it could be anything. To retain backward compatibility though if there is no geometry query field, then the query path will be used. So the format could be point?crs=1234index=yes... Including the index in the URI is useful for me (for the MemoryLayerSaver plugin), as it restores that when the layer is recreated when a project is reopened. I'm not so sure about whether to include the field definitions. And if I do, I'm not sure about the best way to encode them, and whether to include length and precision fields. It would probably be more conventional to use something like name:type:length:precision for each field? Any thoughts. Finally, I'd like to override the dataSourceUri() function to return a definition reflecting the current state of the provider (ie index, fields, etc). This is potentially breaking to plugin code if it uses this to determine the geometry type, not that there is any reason to do so. Cheers Chris -Original Message- From: Martin Dobias [mailto:wonder...@gmail.com] Sent: Saturday, 8 January 2011 7:06 a.m. To: Chris Crook Cc: qgis-developer@lists.osgeo.org Subject: Re: [Qgis-developer] Cleanly create memory layer in Python? On Thu, Jan 6, 2011 at 9:16 PM, Chris Crook ccr...@linz.govt.nz wrote: Hi All I'm wanting to create a memory provider in Python without invoking the CRS selection dialog (even if the QGIS settings are set to Prompt for CRS when a new layer is created. At the moment my code looks like: settings = QSettings() prjSetting = settings.value(/Projections/defaultBehaviour) settings.setValue(/Projections/defaultBehaviour, QVariant()) layer = QgsVectorLayer(point,name,memory) if prjSetting: settings.setValue(/Projections/defaultBehaviour,prjSetting) This does work, but it seems a bit cumbersome (at first glance it doesn't even look like creating a vector layer!), so I'm wondering if there is a cleaner approach.. Hi Chris I agree this is cumbersome. A possible solution would be to extend the URI for memory provider - currently it accepts only a string with geometry type. New syntax could be introduced that would explicitly set layer CRS, e.g. geometry=pointcrs=4326. Any thoughts and patches are welcome. Regards Martin __ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or i...@linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank you. __ ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
Re: [Qgis-developer] Cleanly create memory layer in Python?
On Thu, Jan 6, 2011 at 9:16 PM, Chris Crook ccr...@linz.govt.nz wrote: Hi All I'm wanting to create a memory provider in Python without invoking the CRS selection dialog (even if the QGIS settings are set to Prompt for CRS when a new layer is created. At the moment my code looks like: settings = QSettings() prjSetting = settings.value(/Projections/defaultBehaviour) settings.setValue(/Projections/defaultBehaviour, QVariant()) layer = QgsVectorLayer(point,name,memory) if prjSetting: settings.setValue(/Projections/defaultBehaviour,prjSetting) This does work, but it seems a bit cumbersome (at first glance it doesn't even look like creating a vector layer!), so I'm wondering if there is a cleaner approach.. Hi Chris I agree this is cumbersome. A possible solution would be to extend the URI for memory provider - currently it accepts only a string with geometry type. New syntax could be introduced that would explicitly set layer CRS, e.g. geometry=pointcrs=4326. Any thoughts and patches are welcome. Regards Martin ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
Re: [Qgis-developer] Cleanly create memory layer in Python?
Hi Chris In the 'Profile from lines' plugin I'm using a similar approach: # python code projectionSettingKey = Projections/defaultBehaviour oldProjectionSetting = self.qgisSettings.value(projectionSettingKey) self.qgisSettings.setValue(projectionSettingKey, useGlobal) self.qgisSettings.sync() pointLayer = QgsVectorLayer(Point, temporary_points, memory) pointLayer.setCrs(linesLayer.crs()) self.qgisSettings.setValue(projectionSettingKey, oldProjectionSetting) This was discussed a while back at another thread in this mailing-list (08/09/2010) and this was a suggestion from Martin Dobias. It seems at the moment it is as clean as it gets (its still a bit unclean though ;)) I'd also be interested in knowing alternative ways to do this. On Thu, Jan 6, 2011 at 8:16 PM, Chris Crook ccr...@linz.govt.nz wrote: Hi All I'm wanting to create a memory provider in Python without invoking the CRS selection dialog (even if the QGIS settings are set to Prompt for CRS when a new layer is created. At the moment my code looks like: settings = QSettings() prjSetting = settings.value(/Projections/defaultBehaviour) settings.setValue(/Projections/defaultBehaviour, QVariant()) layer = QgsVectorLayer(point,name,memory) if prjSetting: settings.setValue(/Projections/defaultBehaviour,prjSetting) This does work, but it seems a bit cumbersome (at first glance it doesn't even look like creating a vector layer!), so I'm wondering if there is a cleaner approach.. Cheers Chris __ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or i...@linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank you. __ ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer -- ___ ___ __ Ricardo Garcia Silva ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
