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 _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user