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ICGC-vt-postgis

A set of PostGIS utility functions for generating and instrumenting (Mapbox Vector Tiles)[https://www.mapbox.com/vector-tiles/specification/], used at (Institut Geològic i Cartogràfic de Catalunya - ICGC)[http://www.icgc.cat/] for generating the ContextMaps product.

Requirements

The system has been tested in:

  • PostgreSQL 9.5
  • PostGIS 2.4

But may work with previous versions. Please let us know your experience with other versions.

Installation

Everything is installed in the icgc-vt-postgis-create.sql sql file, so installation boils down to importing this file, eg:

psql -U <username> -d <dbname> -f icgc-vt-postgis-create.sql

Make sure the username has the appropiate privileges to do so.

All functions and expected tables are installed in the icgc_vt schema. To use them from another schema, make sure to fully qualify the schema or to alter the search path.

Filling user data

The system expects two tables to be filled by the user:

layers

This table contains information on which layers will be embedded in each tile protobuffer.

  • name of layer
  • kind of geometry (LineString, Polygon,...).
  • zoom bounds where the layer should appear.
  • SQL returning query.

IMPORTANT: The SQL query must return a geom column with the geometry.

tiles

This table should contain the tile coordinates and envelope for each tile that can be generated in the system. In the data\tiles.sql file you can find an example for the tiles in 3857 schema covering Catalonia between zooms 7-14 (these are the tiles used by ICGC's ContextMaps product).

Usage

Once the data is available in the required tables, generating a VT is as easy as calling the function:

SELECT icgc_vt.tile_pbf(z,x,y);

This returns a binary that can be saved to a file o returned directly to a browser client, etc...

Statistics

When the setting icgc_vt.log_stats is set to on, data regarding the rendering time and size for each layer is logged into the layer_stats table. It is up to the user to reset this table whenever it makes sense.

The standard pattern would be to activate logging and reset the stats table:

DELETE FROM layer_stats;
SELECT pg_catalog.set_config('icgc_vt.log_stats', 'on', false);

Then perform the queries that we would like to analyze, eg:

SELECT icgc_vt.tile_pbf(z,x,y) FROM icgc_vt.tiles;

And then perform any statistical analysis on the results.

Uninstall

Since all data is contained in the icgc_vt schema, removal is just a matter of calling:

DROP SCHEMA icgc_vt CASCADE;