Temporal extension for GRASS GIS 7

Adding the time dimension to GRASS GIS raster, vector and voxel data types for FIELD based applications using a time stamp approach

Time stamps in SQL tables

Raster, vector and voxel maps in GRASS GIS will have temporal attributes by default:

• Creation time
• Modification time
• An absolute or relative time stamp
  • absolute:
    • start date
    • end date
  • relative
    • duration
    • a relative time stamp

To store the time stamps and to enable temporal queries a SQL DBMS, capable of temporal datatypes, will be used. As default a Sqlite3 database will be used to store map specific informations in database files. Additionally Postgresql should be supported too.

In case of SQlite a GRASS SQL database file is created for each mapset in a location. Views are used to access the raster, vector or raster3d map entries of different mapset databases at once.

The time stamps as well as attributes and map specific meta data of all created maps in GRASS GIS will be stored in SQL tables in the GRASS SQL databases. The entries in the SQL tables will be created or updated automatically while creation, modification or removement of maps. For each GRASS datatype (raster, raster3d and vector) four SQL tables will be added to GRASS SQL databases at mapset creation:

• The base table has an equal layout for raster, vector and raster3d maps. This table stores:
  • The id which is of type string. As id the raster, raster3d or vector map names should be used, because these must be unique in a mapset and can be used as primary key
  • The temporal type specifies if the time stamp is relative or absolute
  • The creation date is of type datetime
  • The modification date is of type datetime

• The absolute time table to store the absolute time stamps for each map. The layout is equal for raster, raster3d and vector maps. This table stores:
  • The id as primary key
  • The start time stamp is of type datetime
  • The end time stampis of type datetime
  • The time zoneis of type integer

• The relative time table to store the relative time stamps for each map. The layout is equal for raster, raster3d and vector maps. This table stores:
  • The id as primary key
  • The relative time stamp is of type datetime

A map can only have an absolute or relative time stamp.

• The metadata table is specific for each grass data type. It stores the spatial and temporal extent as well as map specific attributes (creator, range, cell type, features, ...)

In long term these kind of SQL tables may replace the text file based storage of map metadata, database links and time stamps.

New temporal GRASS datatypes

Adding new temporal data types to grass: time and thematic spatio-temporal datasets Spacetime raster, vector and voxel datasets are handled as new data types. Maps can be registered and unregistered in spacetime datasets. Maps are registered by id (name). All relevant spatio-temporal data is availabe in SQL tables. Cross referencing must be implemented (raster maps storing the spacetime raster datasets in which they are registered) Spacetime datasets have absolute or relative time type, these types cant be mixed up but converted Specific metadata for raster spacetime maps The spatial extent computed or updated via trigger from all registered raster maps The temporal extent computed or updated via trigger from all registered raster maps The raster datatype (CELL, FCELL, DCELL, MIXED) Temporal resolution (1s - decades) defining the granularity of the datasets (like the resolution settings for raster/voxel maps) Thematic spacetime datasets will include several spacetime datasets to handle them thematically

The new datatypes are handled like the existing -> registered im mapset specific tables with creation and modification date and absolute/relative time stamp.

Tools: Spacetime modules for registration and un-registration and extraction of raster, voxel and vector maps tr.register, tr.unregister, tr.extract t3.register, t3.unregister, t3.extract tv.register, tv.unregister, tv.extract

Spacetime modules for resampling, interpolation, time stamp snapping and extraction must be implemented.

Extraction is based on where SQL statements or specific time stamps. Interpolated maps are created or existing map ids will be returned. The extraction tool will provide different types of extraction algorithms Nearest neighbour Interpolation (only raster and voxel maps) (linear, quadratic, ...) Last valid time stamp

tr(3).resample -> will create a new spacetime raster (voxel) datasets with a different spatio-temporal resolution, several methods will be available: averaging (mean, median, geometric mean, ...) summation, multiplication max and min functions

Access to spacetime tables must be implemented as GRASS GIS library: Registration and unregistration of maps into spacetime datasets Update/creation of base table entries, so the SQL tables can be modified in low level GRASS GIS library functions (creation, deletion of maps) Selection of maps from spacetime datasets