SpatiaLite

Attributes

location

gaia-gis.it

author

Alessandro Furieri

Summary

The SpatiaLite extension enables SQLite to support spatial data too (aka GIS), in a way conformant to OpenGis specifications

Description

• supports standard WKT and WKB formats
• implements SQL spatial functions such as AsText(), GeomFromText(), Area(), PointN() and alike
• the complete set of OpenGis functions is supported via GEOS, thus comprehending sophisticated spatial analysis functions such as Overlaps(), Touches(), Union(), Buffer() ..
• supports full Spatial metadata along the OpenGis specifications
• supports importing and exporting from / to shapefiles
• supports coordinate reprojection via PROJ.4 and EPSG geodetic parameters dataset
• supports locale charsets via GNU libiconv
• implements a true Spatial Index based on the SQLite's RTree extension

The VirtualShape extension enables SQLite to access shapefiles as VIRTUAL TABLEs

• you can then perform standard SQL queries on external shapefiles, with no need for importing or converting them

The VirtualText extension enables SQLite to access CSV/TxtTab files as VIRTUAL TABLEs

• you can then perform standard SQL queries on external CSV/TxtTab files, with no need for importing or converting them

Spatialite comes in two flavours (since version 4.2.0, see https://www.gaia-gis.it/fossil/libspatialite/wiki?name=mod_spatialite for details):

libspatialite is a classic shared library. It depends on some external libsqlite3. It cannot be used as a dynamic extension via the SELECT load_extension SQLite mechanism.

mod_spatialite is a loadable SQLite module/extension (lacking any explicit SQLite3 dependency). To load and activate this module, call SELECT load_extension in SQLite.

So, in order to use Spatialite from Tcl, you just need the Tcl SQLite3 package and the mod_spatialite library. Then do the following:

package require sqlite3
sqlite3 db someDBfile.db
db enable_load_extension true
db eval {select load_extension('/path/to/spatialsqlite/libdir/mod_spatialite')}
# Note: do not specify the file extension (.so, .dylib, ...) as SQLite does this automagically

Harm Olthof: using tdbc it works like this:

package require tdbc::sqlite3
set db_path {/path/to/sqlitefile.sqlite}
tdbc::sqlite3::connection create db $db_path
set db_handle [db getDBhandle]
$db_handle enable_load_extension 1

# The directory containing dll's for geos, proj4, etc must be added to the PATH environment
append ::env(PATH)  {;} {D:\pshare\bin\spatialite\bin\spatialite-3.0.1-DLL-win-x86}

db allrows {SELECT load_extension('/path/to/spatialsqlite/libraryfile')}

and if it's a new or non-spatialite database file, you should initialize it:

db allrows {SELECT InitSpatialMetaData()}

Another example, now showing how to create a new spatial db and adding some points to it:

package require sqlite3
sqlite3 db :memory:
db enable_load_extension true
db eval {SELECT load_extension('mod_spatialite')}
db eval {SELECT InitSpatialMetaData()}
db eval {CREATE table hal (id integer)}
db eval {SELECT AddGeometryColumn('hal','geometry',-1,'POINT','XY')}
db eval {SELECT CreateSpatialIndex('hal','geometry')}

set n 0
set points [list 1.0 2.0 3.0 4.0 5.0 6.0]
db transaction {
    foreach {x y} $points {
        db eval {
            INSERT into hal ('id','geometry') 
            VALUES (:n, MakePoint(CastToDouble(:x), CastToDouble(:y),-1))
        }
        incr n
    }
}
puts [db eval {SELECT id, AsText(geometry) from hal}]

==> 0 {POINT(1 2)} 1 {POINT(3 4)} 2 {POINT(5 6)}

...  
set lib [file join $env(LD_LIBRARY_PATH) libmod_spatialite]
db eval {SELECT load_extension(:lib)}
...