# LostGIS

## Types

### TPV

    create type TPV as (
        -- position
        geom     geometry(point, 3857),
        accuracy float,
        -- velocity
        heading  float,
        speed    float,
        -- time
        ts       timestamptz,
        -- helpers
        source   text,
        osm_id   bigint
    );

## Functions

### coslat

Get latitude cosine. Works on projected geometries too.

    function coslat(geometry) returns float


### coslat (tpv)

Get cosine from latitude.

    function coslat(tpv) returns float


Direct calculation of `cos(lat)` in `3857` without reprojecting it to `4326`. Used following expression `coslat = cos(asin(tanh(Y / 6378137)))`.

### median

Aggregate function for getting of median

    aggregate median( anyelement )

### project_position

Get new position for given `tpv` and new `timestamp`.

    function project_position(TPV, timestamptz) returns TPV

Calculate new position based on `speed` and `heading` from given `tpv`.

### ST_AnglesEqual

Comparison of two angles

    function ST_AnglesEqual(
        angle1 float,
        angle2 float,
        oneway boolean,
        delta  float default pi() / 4
    ) returns boolean

### ST_AnglesEqualD

Comparison of two angles in degrees.

    function ST_AnglesEqualD(
        angle1 float,
        angle2 float,
        oneway boolean,
        delta  float default 45
    ) returns boolean

### ST_Fast_Real_Buffer.sql

It gets buffer in real meters, in contrast to [ST_Buffer](http://www.postgis.org/docs/ST_Buffer.html) operating in projection units.

    function ST_Fast_Real_Buffer(
        geom geometry, radius float,
        buffer_style_parameters text default ''
    ) returns geometry

### ST_Fast_Real_Length.sql

It gets length in real meters, in contrast to [ST_Length](http://www.postgis.org/docs/ST_Length.html) operating in projection units.

    function ST_Fast_Real_Length(
        geom geometry
    ) returns double precision

### ST_FilterSmallRings.sql

Leaves only large rings in polygon geometry. Useful for map generalization.

    function ST_FilterSmallRings(
        geom     geometry,
        min_area float default 0
    ) returns geometry

### ST_GridCell.sql

Get the geometry of rectangular cell of grid.

    function ST_GridCell(
        point geometry,
        grid_size float default 500
    ) returns geometry

Useful for binning point datasets.

### ST_LargestSubPolygon.sql

Leave a single polygon from a multipolygon geometry.

    function ST_LargestSubPolygon(
        geom geometry
    ) returns geometry

Useful for map generalization.

### ST_LineAngleAtPoint.sql

Given a line and a point at it, find the azimuth of segment the point is closest to.

    function ST_LineAngleAtPoint(
        point geometry,
        line  geometry,
        delta float default 1
    ) returns float

### ST_RealOffsetCurve.sql

Return an offset line at a given distance and side from an input line. Radius is in signed value meters.

    function ST_RealOffsetCurve(
        geom geometry,
        radius float,
        buffer_style_parameters text default ''
    ) returns geometry

### ST_Safe_Difference.sql

Replacement for [ST_Difference](http://www.postgis.org/docs/ST_Difference.html), automatically repairing invalid geometries (see also `ST_Safe_Repair`). 

    function ST_Safe_Difference(
        geom_a           geometry,
        geom_b           geometry default null,
        message          text default '[unspecified]',
        grid_granularity double precision default 1
    ) returns geometry

Also `ST_Safe_Difference(geom, null) = geom`, which is useful in aggregations.

### ST_Safe_Intersection.sql

Replacement for [ST_Intersection](http://www.postgis.org/docs/ST_Intersection.html), automatically repairing invalid geometries (see also `ST_Safe_Repair`).

    function ST_Safe_Intersection(
        geom_a           geometry,
        geom_b           geometry default null,
        message          text default '[unspecified]',
        grid_granularity double precision default 1
    ) returns geometry

### ST_Safe_Repair.sql

Function that tries hard to get a valid geometry out of any geometry.

    function ST_Safe_Repair(
        geom    geometry,
        message text default '[unspecified]'
    ) returns geometry

### ST_TimeLineMerge.sql

Sew together an array of segments of track, where (x,y,z) is mapped to (x,y,timestamp).

    function ST_TimeLineMerge(
        geoms geometry ( linestringz ) []
    ) returns setof geometry ( linestringz )