pointcloud

pointcloud : data type for lidar point clouds

Overview

Packages

Source

Install

Make sure PGDG repo available:

pig repo add pgdg -u    # add pgdg repo and update cache

Install this extension with pig:

pig install pointcloud;		# install via package name, for the active PG version

pig install pointcloud -v 18;   # install for PG 18
pig install pointcloud -v 17;   # install for PG 17
pig install pointcloud -v 16;   # install for PG 16
pig install pointcloud -v 15;   # install for PG 15
pig install pointcloud -v 14;   # install for PG 14

Create this extension with:

CREATE EXTENSION pointcloud;

Usage

pgpointcloud/pointcloud: A PostgreSQL extension for storing point cloud (LIDAR) data

Documentation

PostgreSQL Pointcloud stores point cloud (LIDAR) data in PostgreSQL. It introduces two new data types: PcPoint for individual points and PcPatch for collections of points. Data is organized by schema documents that describe the dimensions and encoding of each point.

CREATE EXTENSION pointcloud;
-- For PostGIS integration:
CREATE EXTENSION pointcloud_postgis;

Concepts

Schemas

PostgreSQL Pointcloud uses a “schema document” to describe the contents of any particular LIDAR point. Each point contains a number of dimensions, and each dimension can be of any data type, with scaling and/or offsets applied to move between the actual value and the value stored in the database. The schema document format is the same one used by the PDAL library.

Here is a simple 4-dimensional schema document:

INSERT INTO pointcloud_formats (pcid, srid, schema) VALUES (1, 4326,
'<?xml version="1.0" encoding="UTF-8"?>
<pc:PointCloudSchema xmlns:pc="http://pointcloud.org/schemas/PC/1.1"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <pc:dimension>
    <pc:position>1</pc:position>
    <pc:size>4</pc:size>
    <pc:description>X coordinate as a long integer. You must use the
                    scale and offset information of the header to
                    determine the double value.</pc:description>
    <pc:name>X</pc:name>
    <pc:interpretation>int32_t</pc:interpretation>
    <pc:scale>0.01</pc:scale>
  </pc:dimension>
  <pc:dimension>
    <pc:position>2</pc:position>
    <pc:size>4</pc:size>
    <pc:description>Y coordinate as a long integer. You must use the
                    scale and offset information of the header to
                    determine the double value.</pc:description>
    <pc:name>Y</pc:name>
    <pc:interpretation>int32_t</pc:interpretation>
    <pc:scale>0.01</pc:scale>
  </pc:dimension>
  <pc:dimension>
    <pc:position>3</pc:position>
    <pc:size>4</pc:size>
    <pc:description>Z coordinate as a long integer. You must use the
                    scale and offset information of the header to
                    determine the double value.</pc:description>
    <pc:name>Z</pc:name>
    <pc:interpretation>int32_t</pc:interpretation>
    <pc:scale>0.01</pc:scale>
  </pc:dimension>
  <pc:dimension>
    <pc:position>4</pc:position>
    <pc:size>2</pc:size>
    <pc:description>The intensity value is the integer representation
                    of the pulse return magnitude. This value is optional
                    and system specific. However, it should always be
                    included if available.</pc:description>
    <pc:name>Intensity</pc:name>
    <pc:interpretation>uint16_t</pc:interpretation>
    <pc:scale>1</pc:scale>
  </pc:dimension>
  <pc:metadata>
    <Metadata name="compression">dimensional</Metadata>
  </pc:metadata>
</pc:PointCloudSchema>');

Schema documents are stored in the pointcloud_formats table, along with a pcid or “pointcloud identifier”. Each object just has a pcid, which serves as a key to find the schema in pointcloud_formats. This is similar to the way the srid is resolved for spatial reference system support in PostGIS.

Point Cloud Objects

PcPoint: The basic point cloud type. Every point has a (large) number of dimensions, but at a minimum an X and Y coordinate. Points can be rendered in JSON form using PC_AsText(pcpoint):

{
    "pcid" : 1,
      "pt" : [0.01, 0.02, 0.03, 4]
}

PcPatch: A collection of PcPoint grouped together. Instead of storing billions of individual point records, LIDAR data is represented as a smaller collection of PcPatch records. Patches are rendered with PC_AsText(pcpatch):

{
    "pcid" : 1,
     "pts" : [
              [0.02, 0.03, 0.05, 6],
              [0.02, 0.03, 0.05, 8]
             ]
}

Tables

-- This requires the schema entry above so that pcid==1 exists.

-- A table of points
CREATE TABLE points (
    id SERIAL PRIMARY KEY,
    pt PCPOINT(1)
);

-- A table of patches
CREATE TABLE patches (
    id SERIAL PRIMARY KEY,
    pa PCPATCH(1)
);

Two system-provided tables are available:

• pointcloud_formats: holds all the pcid entries and schema documents
• pointcloud_columns: a view displaying all columns that contain point cloud objects

SELECT * FROM pointcloud_columns;

 schema |    table    | column | pcid | srid |  type
--------+-------------+--------+------+------+---------
 public | points      | pt     |    1 | 4326 | pcpoint
 public | patches     | pa     |    1 | 4326 | pcpatch

Compressions

Compression is declared in the <pc:metadata> block of the schema document:

<pc:metadata>
  <Metadata name="compression">dimensional</Metadata>
</pc:metadata>

Three supported compression methods:

• None: stores points and patches as byte arrays using type and formats described in the schema document.
• Dimensional: stores patches as collections of dimensional data arrays with “appropriate” compression applied. Makes the most sense for smaller patch sizes.
• LAZ (LASZip): requires Pointcloud built with laz-perf support.

If no compression is declared, none is assumed.

Dimensional compression uses three schemes internally: run-length encoding (for low variability), common bits removal (for narrow bit range variability), and raw deflate compression via zlib.

Functions: Schema

PC_SchemaGetNDims

PC_SchemaGetNDims(pcid integer) returns integer – Return the number of dimensions.

SELECT PC_SchemaGetNDims(1);
-- 18

PC_SchemaIsValid

PC_SchemaIsValid(xml text) returns boolean – Return true if the pointcloud schema is valid.

SELECT PC_SchemaIsValid(schema) FROM pointcloud_formats LIMIT 1;
-- t

Functions: PcPoint

PC_MakePoint

PC_MakePoint(pcid integer, vals float8[]) returns pcpoint – Construct a new pcpoint from a pcid and array of doubles.

SELECT PC_MakePoint(1, ARRAY[-127, 45, 124.0, 4.0]);

-- 010100000064CEFFFF94110000703000000400

Insert test values:

INSERT INTO points (pt)
SELECT PC_MakePoint(1, ARRAY[x,y,z,intensity])
FROM (
  SELECT
  -127+a/100.0 AS x,
    45+a/100.0 AS y,
         1.0*a AS z,
          a/10 AS intensity
  FROM generate_series(1,100) AS a
) AS values;

PC_AsText (point)

PC_AsText(p pcpoint) returns text – Returns a JSON version of the point data.

SELECT PC_AsText('010100000064CEFFFF94110000703000000400'::pcpoint);
-- {"pcid":1,"pt":[-127,45,124,4]}

PC_Get

PC_Get(pt pcpoint) returns float8[] – Returns values of all dimensions in an array.

SELECT PC_Get('010100000064CEFFFF94110000703000000400'::pcpoint);
-- {-127,45,124,4}

PC_Get(pt pcpoint, dimname text) returns numeric – Returns the value of a named dimension.

SELECT PC_Get('010100000064CEFFFF94110000703000000400'::pcpoint, 'Intensity');
-- 4

PC_MemSize (point)

PC_MemSize(pt pcpoint) returns int4 – Returns the memory size of a pcpoint.

SELECT PC_MemSize(PC_MakePoint(1, ARRAY[-127, 45, 124.0, 4.0]));
-- 25

PC_PCId (point)

PC_PCId(p pcpoint) returns integer – Returns the pcid schema number of this point.

SELECT PC_PCId('010100000064CEFFFF94110000703000000400'::pcpoint);
-- 1

Functions: PcPatch

PC_Patch

PC_Patch(pts pcpoint[]) returns pcpatch – Aggregate function that collects pcpoint values into a pcpatch.

INSERT INTO patches (pa)
SELECT PC_Patch(pt) FROM points GROUP BY id/10;

PC_MakePatch

PC_MakePatch(pcid integer, vals float8[]) returns pcpatch – Construct a new pcpatch from a pcid and array of doubles (array size must be a multiple of dimension count).

SELECT PC_AsText(PC_MakePatch(1, ARRAY[-126.99,45.01,1,0, -126.98,45.02,2,0, -126.97,45.03,3,0]));

-- {"pcid":1,"pts":[
--  [-126.99,45.01,1,0],[-126.98,45.02,2,0],[-126.97,45.03,3,0]
-- ]}

PC_AsText (patch)

PC_AsText(p pcpatch) returns text – Returns a JSON version of the patch data.

SELECT PC_AsText(pa) FROM patches LIMIT 1;

-- {"pcid":1,"pts":[
--  [-126.99,45.01,1,0],[-126.98,45.02,2,0],[-126.97,45.03,3,0],
--  [-126.96,45.04,4,0],[-126.95,45.05,5,0],[-126.94,45.06,6,0],
--  [-126.93,45.07,7,0],[-126.92,45.08,8,0],[-126.91,45.09,9,0]
-- ]}

PC_Summary

PC_Summary(p pcpatch) returns text – Returns a JSON formatted summary of the patch data.

SELECT PC_Summary(pa) FROM patches LIMIT 1;

-- {"pcid":1, "npts":9, "srid":4326, "compr":"dimensional",
--  "dims":[{"pos":0,"name":"X","size":4,"type":"int32_t","compr":"sigbits",
--           "stats":{"min":-126.99,"max":-126.91,"avg":-126.95}}, ...]}

PC_NumPoints

PC_NumPoints(p pcpatch) returns integer – Returns the number of points in a patch.

SELECT PC_NumPoints(pa) FROM patches LIMIT 1;
-- 9

PC_PCId (patch)

PC_PCId(p pcpatch) returns integer – Returns the pcid schema number of the patch.

PC_MemSize (patch)

PC_MemSize(p pcpatch) returns int4 – Returns the memory size of a pcpatch.

PC_Explode

PC_Explode(p pcpatch) returns SetOf[pcpoint] – Set-returning function converting a patch to individual point records.

SELECT PC_AsText(PC_Explode(pa)), id
FROM patches WHERE id = 7;

              pc_astext               | id
--------------------------------------+----
 {"pcid":1,"pt":[-126.5,45.5,50,5]}   |  7
 {"pcid":1,"pt":[-126.49,45.51,51,5]} |  7
 {"pcid":1,"pt":[-126.48,45.52,52,5]} |  7
 ...

PC_PointN

PC_PointN(p pcpatch, n int4) returns pcpoint – Returns the n-th point (1-based). Negative n counts from the end.

PC_Range

PC_Range(p pcpatch, start int4, n int4) returns pcpatch – Returns a patch containing n points starting from the start-th point (1-based).

PC_Union

PC_Union(p pcpatch[]) returns pcpatch – Aggregate function that merges pcpatch entries into a single pcpatch.

SELECT PC_NumPoints(PC_Union(pa)) FROM patches;
-- 100

PC_Intersects (patch-patch)

PC_Intersects(p1 pcpatch, p2 pcpatch) returns boolean – Returns true if the bounds of p1 intersect the bounds of p2.

PC_PatchAvg

PC_PatchAvg(p pcpatch, dimname text) returns numeric – Returns the average value of a named dimension across all points.

SELECT PC_PatchAvg(pa, 'intensity') FROM patches WHERE id = 7;
-- 5.0000000000000000

PC_PatchAvg(p pcpatch) returns pcpoint – Returns a PcPoint with average values of each dimension.

SELECT PC_AsText(PC_PatchAvg(pa)) FROM patches WHERE id = 7;
-- {"pcid":1,"pt":[-126.46,45.54,54.5,5]}

PC_PatchMin

PC_PatchMin(p pcpatch, dimname text) returns numeric – Returns the minimum value of a named dimension.

PC_PatchMin(p pcpatch) returns pcpoint – Returns a PcPoint with the minimum values of each dimension.

PC_PatchMax

PC_PatchMax(p pcpatch, dimname text) returns numeric – Returns the maximum value of a named dimension.

PC_PatchMax(p pcpatch) returns pcpoint – Returns a PcPoint with the maximum values of each dimension.

PC_FilterGreaterThan

PC_FilterGreaterThan(p pcpatch, dimname text, float8 value) returns pcpatch – Filter points with values greater than the given value.

SELECT PC_AsText(PC_FilterGreaterThan(pa, 'y', 45.57))
FROM patches WHERE id = 7;

-- {"pcid":1,"pts":[[-126.42,45.58,58,5],[-126.41,45.59,59,5]]}

PC_FilterLessThan

PC_FilterLessThan(p pcpatch, dimname text, float8 value) returns pcpatch – Filter points with values less than the given value.

PC_FilterEquals

PC_FilterEquals(p pcpatch, dimname text, float8 value) returns pcpatch – Filter points with values equal to the given value.

PC_FilterBetween

PC_FilterBetween(p pcpatch, dimname text, float8 value1, float8 value2) returns pcpatch – Filter points with values between (excluding) value1 and value2.

PC_Sort

PC_Sort(p pcpatch, dimnames text[]) returns pcpatch – Returns a copy of the patch lexicographically sorted along the given dimensions.

PC_IsSorted

PC_IsSorted(p pcpatch, dimnames text[], strict boolean default true) returns boolean – Checks whether a pcpatch is sorted lexicographically. The strict option checks for no duplicates.

PC_SetPCId

PC_SetPCId(p pcpatch, pcid int4, def float8 default 0.0) returns pcpatch – Sets the schema on a PcPatch. For dimensions in the new schema but not in the old, the value def is used (default 0.0).

PC_Transform

PC_Transform(p pcpatch, pcid int4, def float8 default 0.0) returns pcpatch – Returns a new patch with data transformed based on the target schema. Unlike PC_SetPCId, this may change patch data if interpretations, scales or offsets differ.

PC_Compress

PC_Compress(p pcpatch, global_compression_scheme text, compression_config text) returns pcpatch – Compress a patch with a manually specified scheme.

Allowed global compression schemes: auto, laz, dimensional. For dimensional, the config is a comma-separated list of per-dimension compressions: auto, zlib, sigbits, rle.

PC_Uncompress

PC_Uncompress(p pcpatch) returns pcpatch – Returns an uncompressed version (compression type none). Must be the outer function in your query to return uncompressed data on the wire.

Functions: WKB

PC_AsBinary (point)

PC_AsBinary(p pcpoint) returns bytea – Return the OGC “well-known binary” format for the point.

PC_EnvelopeAsBinary

PC_EnvelopeAsBinary(p pcpatch) returns bytea – Return the OGC WKB for the 2D bounds of the patch.

Note: PC_Envelope is a deprecated alias for PC_EnvelopeAsBinary.

PC_BoundingDiagonalAsBinary

PC_BoundingDiagonalAsBinary(p pcpatch) returns bytea – Return the OGC WKB for the bounding diagonal of the patch.

Functions: PostGIS Integration

The pointcloud_postgis extension adds functions for using Pointcloud with PostGIS, converting PcPoint and PcPatch to Geometry and doing spatial filtering.

CREATE EXTENSION postgis;
CREATE EXTENSION pointcloud;
CREATE EXTENSION pointcloud_postgis;

Geometry Cast

Geometry(pcpoint) returns geometry / pcpoint::geometry – Casts PcPoint to PostGIS geometry, mapping x/y/z/m.

SELECT ST_AsText(PC_MakePoint(1, ARRAY[-127, 45, 124.0, 4.0])::geometry);
-- POINT Z (-127 45 124)

PC_EnvelopeGeometry

PC_EnvelopeGeometry(pcpatch) returns geometry – Returns the 2D bounds as a PostGIS Polygon 2D.

SELECT ST_AsText(PC_EnvelopeGeometry(pa)) FROM patches LIMIT 1;
-- POLYGON((-126.99 45.01,-126.99 45.09,-126.91 45.09,-126.91 45.01,-126.99 45.01))

Useful for creating an index:

CREATE INDEX ON patches USING GIST(PC_EnvelopeGeometry(patch));

PC_BoundingDiagonalGeometry

PC_BoundingDiagonalGeometry(pcpatch) returns geometry – Returns the bounding diagonal as a LineString (2D/Z/M/ZM based on available dimensions).

SELECT ST_AsText(PC_BoundingDiagonalGeometry(pa)) FROM patches;
-- LINESTRING Z (-126.99 45.01 1,-126.91 45.09 9)

Useful for creating a ND index:

CREATE INDEX ON patches USING GIST(PC_BoundingDiagonalGeometry(patch) gist_geometry_ops_nd);

PC_Intersection

PC_Intersection(pcpatch, geometry) returns pcpatch – Returns a PcPatch containing only points that intersect the geometry.

SELECT PC_AsText(PC_Explode(PC_Intersection(
      pa,
      'SRID=4326;POLYGON((-126.451 45.552, -126.42 47.55, -126.40 45.552, -126.451 45.552))'::geometry
)))
FROM patches WHERE id = 7;

             pc_astext
--------------------------------------
 {"pcid":1,"pt":[-126.44,45.56,56,5]}
 {"pcid":1,"pt":[-126.43,45.57,57,5]}
 {"pcid":1,"pt":[-126.42,45.58,58,5]}
 {"pcid":1,"pt":[-126.41,45.59,59,5]}

PC_Intersects (patch-geometry)

PC_Intersects(p pcpatch, g geometry) returns boolean / PC_Intersects(g geometry, p pcpatch) returns boolean – Returns true if the bounds of the patch intersect the geometry.

SELECT PC_Intersects('SRID=4326;POINT(-126.451 45.552)'::geometry, pa)
FROM patches WHERE id = 7;
-- t

Functions: Utils

PC_Version / PC_Lib_Version / PC_Script_Version

SELECT PC_Version();           -- 1.2.5
SELECT PC_Lib_Version();       -- 1.2.5 2346cc2
SELECT PC_Script_Version();    -- 1.2.5
SELECT PC_Full_Version();
-- POINTCLOUD="1.2.5 2346cc2" PGSQL="170" LIBXML2="2.14.3 LAZPERF enabled=false

PC_Lazperf_Enabled

PC_Lazperf_Enabled() returns boolean – Returns true if LAZperf compression support is available.

Loading Data with PDAL

PDAL is used to load LIDAR files into PostgreSQL Pointcloud. A PDAL pipeline is a JSON file declaring readers, filters, and writers.

Example pipeline to load a LAS file:

{
  "pipeline":[
    {
      "type":"readers.las",
      "filename":"/home/lidar/st-helens-small.las",
      "spatialreference":"EPSG:26910"
    },
    {
      "type":"filters.chipper",
      "capacity":400
    },
    {
      "type":"writers.pgpointcloud",
      "connection":"host='localhost' dbname='pc' user='lidar' password='lidar' port='5432'",
      "table":"sthsm",
      "compression":"dimensional",
      "srid":"26910"
    }
  ]
}

Execute with:

pdal pipeline --input pipelinefile.json

The filters.chipper groups unordered points into compact patches for efficient storage.

PDAL Writer Options

• connection: PostgreSQL connection string
• table: Table to write patches to
• schema: Schema to create the table in (optional)
• column: Column name for patches (default: pa)
• compression: Patch compression format (default: dimensional)
• overwrite: Replace any existing table (default: true)
• srid: Spatial reference id (default: 4326)
• pcid: An existing PCID to use (optional)
• pre_sql / post_sql: SQL to execute before/after pipeline (optional)

PDAL Reader Options

• connection: PostgreSQL connection string
• table: Table to read patches from
• schema: Schema to read from (optional)
• column: Column name to read (default: pa)
• where: SQL where clause to constrain the query (optional)
• spatialreference: Override the database SRID (optional)

Example pipeline to read and export:

{
  "pipeline":[
    {
      "type":"readers.pgpointcloud",
      "connection":"host='localhost' dbname='pc' user='lidar' password='lidar' port='5432'",
      "table":"sthsm",
      "column":"pa",
      "spatialreference":"EPSG:26910",
      "where":"PC_Intersects(pa, ST_MakeEnvelope(560037.36, 5114846.45, 562667.31, 5118943.24, 26910))"
    },
    {
      "type":"writers.text",
      "filename":"/home/lidar/st-helens-small-out.txt"
    }
  ]
}