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PostGIS MVT Provider

The PostGIS MVT provider manages querying for tile requests against a Postgres database (version 12+) with the PostGIS(version 3.0+) extension installed and leverages ST_AsMVT to handle the MVT encoding at the database.

The connection between tegola and PostGIS is configured in a tegola.toml file. An example minimum connection config:

[[providers]]
name = "test_postgis"       # provider name is referenced from map layers (required)
type = "mvt_postgis"        # the type of data provider must be "mvt_postgis" for this data provider (required)
uri = "postgres://postgres:postgres@localhost:5432/tegola"          # PostGIS database uri (required)

Connection Properties

Establishing a connection via connection string (uri) will become the default connection method as of v0.16.0. Connecting via host/port/database is deprecated.

  • name (string): [Required] provider name is referenced from map layers.
  • type (string): [Required] the type of data provider. must be "postgis" to use this data provider
  • uri (string): [Required] PostGIS database uri (postgres://user:password@host:port/database)
  • srid (int): [Optional] The default SRID for the provider. Defaults to WebMercator (3857) but also supports WGS84 (4326)

Connection string properties

Example

# {protocol}://{user}:{password}@{host}:{port}/{database}?{options}=
postgres://tegola:supersecret@localhost:5432/tegola?sslmode=prefer&pool_max_conns=10

Options

Tegola uses pgx to manage PostgresSQL connections that allows the following configurations to be passed as parameters.

  • sslmode: [Optional] PostGIS SSL mode. Default: "prefer"
  • pool_min_conns: [Optional] The min connections to maintain in the connection pool. Defaults to 100. 0 means no max.
  • pool_max_conns: [Optional] The max connections to maintain in the connection pool. Defaults to 100. 0 means no max.
  • pool_max_conn_idle_time: [Optional] The maximum time an idle connection is kept alive. Defaults to "30m".
  • pool_max_connection_lifetime [Optional] The maximum time a connection lives before it is terminated and recreated. Defaults to "1h".
  • pool_max_conn_lifetime_jitter [Optional] Duration after max_conn_lifetime to randomly decide to close a connection.
  • pool_health_check_period [Optional] Is the duration between checks of the health of idle connections. Defaults to 1m

Provider Layers

In addition to the connection configuration above, Provider Layers need to be configured. A Provider Layer tells tegola how to query PostGIS for a certain layer. When using the PostGIS MVT Provider the ST_AsMVTGeom() MUST be used. An example minimum config using the sql config option:

[[providers.layers]]
name = "landuse"
# MVT data provider must use SQL statements
# this table uses "geom" for the geometry_fieldname and "gid" for the id_fieldname so they don't need to be configured
# Wrapping the geom with ST_AsMVTGeom is required.
sql = "SELECT ST_AsMVTGeom(geom,!BBOX!) AS geom, gid FROM gis.landuse WHERE geom && !BBOX!"

Provider Layers Properties

  • name (string): [Required] the name of the layer. This is used to reference this layer from map layers.
  • geometry_fieldname (string): [Optional] the name of the filed which contains the geometry for the feature. defaults to geom.
  • id_fieldname (string): [Optional] the name of the feature id field. defaults to gid.
  • geometry_type (string): [Optional] the layer geometry type. If not set, the table will be inspected at startup to try and infer the gemetry type. Valid values are: Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon, GeometryCollection.
  • srid (int): [Optional] the SRID of the layer. Supports 3857 (WebMercator) or 4326 (WGS84).
  • sql (string): [Required] custom SQL to use use. Supports the following tokens:
    • !BBOX! - [Required] will be replaced with the bounding box of the tile before the query is sent to the database. !bbox! and!BOX! are supported as well for compatibilitiy with queries from Mapnik and MapServer styles.
    • !X! - [Optional] will replaced with the "X" value of the requested tile.
    • !Y! - [Optional] will replaced with the "Y" value of the requested tile.
    • !Z! - [Optional] will replaced with the "Z" value of the requested tile.
    • !ZOOM! - [Optional] will be replaced with the "Z" (zoom) value of the requested tile.
    • !SCALE_DENOMINATOR! - [Optional] scale denominator, assuming 90.7 DPI (i.e. 0.28mm pixel size)
    • !PIXEL_WIDTH! - [Optional] the pixel width in meters, assuming 256x256 tiles
    • !PIXEL_HEIGHT! - [Optional] the pixel height in meters, assuming 256x256 tiles
    • !ID_FIELD! - [Optional] the id field name
    • !GEOM_FIELD! - [Optional] the geom field name
    • !GEOM_TYPE! - [Optional] the geom type if defined otherwise ""

Example mvt_postgis and map config

[[providers]]
name = "test_postgis"
type = "mvt_postgis"
uri = "postgres://postgres:postgres@localhost:5432/tegola"

  [[providers.layers]]
  name = "landuse"
  sql = "SELECT ST_AsMVTGeom(geom,!BBOX!) AS geom, gid FROM gis.landuse WHERE geom && !BBOX!"

[[maps]]
name = "cities"
center = [-90.2,38.6,3.0]  # where to center of the map (lon, lat, zoom)

  [[maps.layers]]
  name = "landuse"
  provider_layer = "test_postgis.landuse"
  min_zoom = 0
  max_zoom = 14

Example mvt_postgis and map config for SRID 4326

When using a 4326 projection with ST_AsMVT the SQL statement needs to be modified. ST_AsMVTGeom is expecting data in 3857 projection so the geometries and the !BBOX! token need to be transformed prior to ST_AsMVTGeom processing them. For example:

[[providers]]
name = "test_postgis"
type = "mvt_postgis"
uri = "postgres://postgres:postgres@localhost:5432/tegola"
srid = 4326 # setting the srid on the provider to 4326 will cause the !BBOX! value to use the 4326 projection.

  [[providers.layers]]
  name = "landuse"
  # the !BBOX! token used in the WHERE clause is not reprojected so it can match 4326 data
  # the matched data AND the !BBOX! are then reporojected to 3857 prior to being passed to ST_AsMVTGeom
  sql = "SELECT ST_AsMVTGeom(ST_Transform(geom, 3857),ST_Transform(!BBOX!,3857)) AS geom, gid FROM gis.landuse WHERE geom && !BBOX!"

[[maps]]
name = "cities"
center = [-90.2,38.6,3.0]  # where to center of the map (lon, lat, zoom)

  [[maps.layers]]
  name = "landuse"
  provider_layer = "test_postgis.landuse"
  min_zoom = 0
  max_zoom = 14

Testing

Testing is designed to work against a live PostGIS database. To see how to set up a database check this github actions script. To run the PostGIS tests, the following environment variables need to be set:

$ export RUN_POSTGIS_TESTS=yes
$ export PGURI="postgres://postgres:postgres@localhost:5432/tegola"
$ export PGURI_NO_ACCESS="postgres://tegola_no_access:postgres@localhost:5432/tegola" # used for testing errors when user does not have read permissions on a table
$ export PGPASSWORD=""
$ export PGSSLMODE="disable"

If you're testing SSL, the following additional env vars can be set:

$ export PGSSLMODE="" // disable, allow, prefer, require, verify-ca, verify-full
$ export PGSSLKEY=""
$ export PGSSLCERT=""
$ export PGSSLROOTCERT=""