AnalyticDB:Raster model

Overview

Raster data consists of a matrix of cells or pixels that are organized into rows and columns (or grids). Each cell contains a value that represents information, such as temperature.

Raster data can be digital aerial photographs, satellite images, digital images, or scanned maps.

GanosBase implements a raster model in AnalyticDB for PostgreSQL. This allows AnalyticDB for PostgreSQL to store and analyze raster data in a cost-effective manner by using database technologies and methods.

Quick start

• Create extensions.

  Create extension ganos_spatialref;
  Create extension ganos_geometry;
  Create Extension Ganos_Raster;

• Create a raster table.

  -- Specify the raster_obj column as the distribution column of the table.
  Create Table raster_table(id integer, raster_obj raster) 
  DISTRIBUTED BY (raster_obj);

• Import raster data from Object Storage Service (OSS).

  Insert into raster_table 
  Values(1, ST_ImportFrom('chunk_table','OSS://<id>:<key>@oss-cn.aliyuncs.com/mybucket/data/my_image.tif')),
  (2, ST_CreateRast('OSS://<id>:<key>@oss-cn.aliyuncs.com/mybucket/data/my_image.tif'));

• Query raster object information.

  Select ST_Height(raster_obj),ST_Width(raster_obj) From raster_table Where id = 1;
   st_height 
  -----------
        1241
  (1 rows)

• Create a pyramid.

  DO $$
  declare
      rast raster;
  begin
      select raster_obj into rast from raster_table where id = 1;
      rast = st_buildpyramid(rast);
      update raster_table set raster_obj = rast where id = 1;
  end;    
  $$ LANGUAGE 'plpgsql';
  
  DO $$
  declare
      rast raster;
  begin
      select raster_obj into rast from raster_table where id = 2;
      rast = st_buildpyramid(rast, -1, 'Near', 'chunk_table');
      update raster_table set raster_obj = rast where id = 2;
  end;    
  $$ LANGUAGE 'plpgsql';

• Calculate the optimal pyramid level based on the world coordinate range, width, and height of a viewport.

  Select ST_BestPyramidLevel(rast, '((128.0, 30.0),(128.5, 30.5))', 800, 600) from raster_table where id = 1;
  
  ---------------------
  3

• Retrieve a pixel matrix from the specified coordinate range of a raster object.

  DO $$
  declare
      rast raster;
  begin
      select raster_obj into rast from raster_table where id = 1;
      rast = st_buildpyramid(rast);
      Select ST_Clip(rast, 0, '((128.980,30.0),(129.0,30.2))', 'World');
  end;    
  $$ LANGUAGE 'plpgsql';

• Calculate the pixel coordinate range of a clipped raster area.

  Select ST_ClipDimension(raster_obj, 2, '((128.0, 30.0),(128.5, 30.5))') 
  from raster_table where id = 1;
  
  ------------------------------------
  '((600, 720),(200, 300))'

• Delete extensions.

  DROP Extension Ganos_Raster;
  DROP extension ganos_geometry;
  DROP extension ganos_spatialref;

SQL reference

For more information, see Terms.