[GRASS-user] Linking multidimensional data to a single point

[Rich Shepard]

On Sun, 15 Mar 2015, Andy Wickert wrote:

> So to boil it down to the simplest part of what you said, the key is just
> to have an ID column in the GRASS table that links to a table in a
> database structure outside of GRASS?

Andy,

   Yes. You can keep all point attributes in SQLite (or other rdbms) tables
rather than in GRASS. It's been a while since I last did this so the
specifics are not immediately available. I would link each point to a table
which describes it; perhaps including geographic coordinates, name, and
other information. Then your discharge and sediment data are in other tables
that are related to each row in the main table. This also allows you to run
SQL queries on the data (such as descriptice statistics) outside of GRASS.

> Just to make sure that I was clear: the problem is how to include multiple
> rows of data that all correspond to just one point in GIS (so "grain size"
> with frequencies in each grain size class or "discharge" with discharges
> at different times).

   Database design is a topic of itself. Separate attribute data from the
spatial data; the former goes into a database (multiple tables), the latter
in GRASS files.

   In your initial message you describe three different categories of data
and each should be in its own table. Information about each data collection
point (which is seen on the map) is in one table. This could include a site
ID as the primary key, site name, perhaps the stream or drainage basin in
which it is located, and other information about the location itself.

   Your second table contains hydaulic data: sample ID (the primary key),
station ID (which relates that row to your point), collection date and time,
discharge, channel width, and any other relevant information.

   Your third table contains sediment data: sample ID (primary key), station
ID, date and time, each grain category (e.g., silt, clay, fine sand, coarse
sand, gravel, cobble), and the percentage or proportion (dry weight?) of
each.

   You could also have additional tables if you want to store more categories
of data for each point.

Hope this helps,

Rich