ST_AsGDALRaster
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名称

ST_AsGDALRaster — 以指定的 GDAL 栅格格式返回栅格图块。 栅格格式是编译库支持的格式之一。 使用 ST_GDALDrivers() 获取您的库支持的格式列表。

大纲

bytea ST_AsGDALRaster(raster rast, text format, text[] options=NULL, integer srid=sameassource);

Description

返回指定格式的栅格图块。 参数逐项列举如下：

  • format 格式来输出。 这取决于 libgdal 库中编译的驱动程序。 通常可用的有“JPEG”、“GTIff”、“PNG”。 使用 ST_GDALDrivers获取您的库支持的格式列表。

  • options GDAL 选项的文本数组。 有效选项取决于格式。 有关更多详细信息，请参阅 GDAL 栅格格式选项。

  • srid the spatial reference identifier to embed in the output raster

可用性：2.0.0 - 需要 GDAL >= 1.6.0。

示例

Export multiple raster tiles as a single JPEG image with 50 percent quality.

Code
SELECT ST_AsGDALRaster(ST_Union(rast), 'JPEG', ARRAY['QUALITY=50']) As rastjpg
FROM dummy_rast
WHERE rast && ST_MakeEnvelope(10, 10, 11, 11);

One way to export raster into another format is using PostgreSQL large object export functions. The following repeats the JPEG example and exports the result. Note that this requires superuser access because it uses server-side large object functions. It will also export to path on server network. If you need export locally, use the psql equivalent lo_ functions which export to the local file system instead of the server file system.

Code
DROP TABLE IF EXISTS tmp_out ;

CREATE TABLE tmp_out AS
SELECT lo_from_bytea(
       0,
       ST_AsGDALRaster(ST_Union(rast), 'JPEG', ARRAY['QUALITY=50'])
        ) AS loid
  FROM dummy_rast
WHERE rast && ST_MakeEnvelope(10, 10, 11, 11);

SELECT lo_export(loid, '/tmp/dummy.jpg')
   FROM tmp_out;

SELECT lo_unlink(loid)
  FROM tmp_out;

Export a raster as a GeoTIFF using the default creation options.

Code
SELECT ST_AsGDALRaster(rast, 'GTiff') AS rasttiff
FROM dummy_rast WHERE rid = 2;

Export a GeoTIFF using JPEG compression at 90 percent quality and embed SRID 4269.

Code
SELECT ST_AsGDALRaster(
  rast,
  'GTiff',
  ARRAY['COMPRESS=JPEG', 'JPEG_QUALITY=90'],
  4269) AS rasttiff
FROM dummy_rast WHERE rid = 2;