[GRASS-user] Clarifying use of postgres/postgis

[Dheeraj Chand]

‘’’

When importing a shapefile or other vector data, only the attrib tables get saved to some database: sqlite by default, or PostgrSQL if you have configured for that backend. But the geometry is still kept in the GRASS vector format.
‘’’

1. How would one configure that? Please assume that I am unfamiliar and uncomfortable with GRASS when explaining, but able to read Java and Python man pages with ease, also comfortable with PSQL and PostGIS.
2. Would we get all the speed benefits of PSQL, would it be used for computations whenever possible?
3. Is there a way to easily move from GRASS and PSQL geometry and topology models when doing this?

Sent from my iPhone

> On Aug 15, 2020, at 7:50 AM, Rich Shepard <rshepard at appl-ecosys.com> wrote:
> 
> On Sat, 15 Aug 2020, Micha Silver wrote:
> 
>> But again, don't confuse - this is NOT PostGIS, and GRASS does not
>> need/use PostGIS for geometry. GRASS geometry is always independent of any
>> external geospatial format.
> 
> Micha,
> 
> Thanks for clarifying; I must have mis-understood what I read. I assumed the
> geometry was kept by GRASS and didn't know why PostGIS was mentioned ... and
> I don't recall just where I read all this.
> 
>> It's the other way around: When you export GRASS map layers, you can, as
>> you know, choose to save out to several formats: shp, Geopackage (the
>> current default) or to PostGIS. PostGIS is the best choice when you need
>> multiuser access to the geospatial data. But you point out that you're the
>> only user, so why would you need the overhead of PostGIS?
> 
> Ah, so. I don't.
> 
>> To repeat, you can set the default for saving attribute tables to
>> PostgreSQL, but do not try to save a GRASS layer to PostGIS in the same
>> database! That will definitely lead to trouble. If you want/need a PostGIS
>> instance for some reason independent of GRASS, then keep it totally
>> separated from GRASS. i.e. at least in a separate schema or even separate
>> database.
> 
> No, I want the attribute data in postgres so I need to learn to make that
> the default.
> 
>> The main reasons for choosing PostgreSQL as your database backend would be
>> 
>> 1. to allow fancy SQL queries on the database tables
>> 2. huge, complex data tables or triggers
>> 3. multiuser access to the attribute tables
> 
> My reason is keeping these data in the same format as other project data.
> 
>> But keep in mind that the default sqlite database is quite powerful, and you would have to look very deeply to find a PostgreSQL feature that is missing in sqlite.
> 
> Yes, I've been using SQlite as long as I have PostgreSQL.
> 
> Thanks,
> 
> Rich
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