postgis-vt-util

postgres helper functions for making vector tiles in Mapbox Studio

z

Given the !scale_denominator! mapnik token, returns a zoom level. Lets you to control at which zoom levels features appear.

Arguments: !scale_denominator! [mapnik token]

Example:

( SELECT
    some, attributes,
    geom_generalized
  FROM your_table
  where z(!scale_denominator!) in (10,11,12)
  union ALL
  SELECT
    some, attributes,
    geom_not_generalized
  FROM your_table
  where z(!scale_denominator!) >= 13
) as data

labelgrid

De-duplicates features based on a given grid size, letting you control feature density. All features are snapped to a grid, but only 1 feature per grid cell is returend when selecting DISTINCT ON the labelgrid function.

Arguments: geometry [geometry], grid size [an integer that divides evenly into 256], !pixel_width! [mapnik token]

Example:

( SELECT
    disctinct on(labelgrid(geom, 128, !pixel_width!))
    some, other, attributes
  FROM your_table
) AS data

linelabel

Select only those line geometries long enough to be labeled; drops all line geometries too short for mapnik to place a label. Linelabel compares line length to the length of a user-supplied label field.

Arguments: zoom [integer], label [text field], geometry [geometry]

Example:

( SELECT
    name, geom
  FROM your_table
  WHERE linelabel(z(!scale_denominator!), name, geom)
) AS data

merc_buffer

Wrapper for ST_Buffer that adjusts distance by latitude to approximate real-world measurements. Assumes input geometries are Web Mercator and input distances are real-world meters. Accuracy decreases for larger buffer distances and at extreme latitudes.

Arguments: geometry [geometry], distance in meters [numeric]

merc_dwithin

Wrapper for ST_DWithin that adjusts distance by latitude to approximate real-world measurements. Assumes input geometries are Web Mercator and input distances are real-world meters. Accuracy decreases for larger distances and at extreme latitudes.

Arguments: geometry a [geometry], geometry b [geometry], distance in meters [numeric]

merc_length

Wrapper for ST_Length that adjusts distance by latitude to approximate real-world measurements. Assumes input geometries are Web Mercator. Accuracy decreases for larger y-axis ranges of the input.

Arguments: geometry [geometry]

tile_bbox

Given a Web Mercator tile ID as (z, x, y), returns a bounding-box geometry of the area covered by that tile.

Arguments: zoom_level [integer], x_tile [integer], y_tile [integer]