[Qgis-developer] Spatialize attribute columns XY oor WKT, design choice

[Régis Haubourg]

Hi, 
Users here ask us a good reliable way to spatialize data from XY or WKT
columns and I'm wondering what could be the reference architecture to have
it in core. I am aware of Xytools plugins, delimited text import and
RTQspider plugin, and also of VRT GDAL format. Questions here are for 2.3
branch or later. 

Here are the functionnal requirements:
 
- The action MUST allow to spatialize XY columns (cartesian or DMS units)
from ANY OPENED data source attribute fields. 
- the action MUST be referenced in vector menu, AND in vector layer's
contextual menu. 
- Geometry and attributes MUST be in sync with origin data source.  
- Spatialized data source SHOULD be correctly imported or linked in another
project (embed project, import project plugin).
- Geometry MUST not be editable to avoid conflicts with attribute or
geometric editions. User should then save as a real spatial data source to
edit geometries.
- the user MUST be able to declare attribute field's SRS so that
reprojection handles correctly. 
- the user should be able to spatialize only a selection or a feature subset
(not sure about it)
- refresh of data should work even if no additionnal plugin is loaded
(dangerous for user experience).
- attributes index and spatial index should be generated in memory. 

quite simple, but no plugin does satisfy all use cases. We have either
replication of data, or direct access only for some specific data sources
(csv, xls, ods.. )

Mapinfo does it but geometry is static and must be refeshed by calling the
action another time. Mapinfo can use sub selections. 
Arcmap only refreshes content on project reload. Grouped with  linear
referening event actions in UI. Not editable

Any opinions on the best implementation architecture? 

As i'm only developping with python, I have be exploring Memory layers,
plugin layers, but it is still unclear to me if this is possible without
declaring a new virtual provider using attributes from on data source. 

VRT is IMHO no adaptated since it is not dynamic with csv data, GDAL lacks
many options to open correctly csv (text delimiters, decimal delimiters...)
. This is why delimited text exists. It also has no spatial index. 
It still remains extremly powerfull for UNION, spatial queries thanks to SQL
dialect...


I would be glad to here from you, so that I can write some specs and hire a
dev. 

Cheers, 
Régis





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