查询栅格数据的坐标系
select st_srid(rast) from raster_table_name
导出指定地理范围的tiff
SELECT ST_AsTIFF(rast, 'LZW') FROM ( SELECT ST_Union(ST_Clip(rast,geom)) AS rast FROM sjy CROSS JOIN (select geom from xingzheng where gid = '24') As geom WHERE ST_Intersects(rast,geom) ) AS rasttiff;
