Name
ST_BandIsNoData — 如果波段仅填充无数据值，则返回 true。
Synopsis
boolean ST_BandIsNoData(raster rast, integer band, boolean forceChecking=false);
boolean ST_BandIsNoData(raster rast, boolean forceChecking=false);
描述
如果波段仅填充无数据值，则返回 true。 如果未指定，则假定波段为1。 如果最后一个参数为 TRUE，则逐像素检查整个波段。 否则，该函数仅返回该带的 isnodata 标志的值。 如果未指定，此参数的默认值为 FALSE。
可用性: 2.0.0
![[Note]](../images/note.png)
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If the flag is dirty (this is, the result is different using TRUE as last parameter and not using it) you should update the raster to set this flag to true, by using ST_SetBandIsNoData(), or ST_SetBandNoDataValue() with TRUE as last argument. See ST_SetBandIsNoData. |
示例
This example creates a dummy table with one raster column.
create table dummy_rast (rid integer, rast raster);
-- Add raster with two bands, one pixel/band. In the first band, nodatavalue = pixel value = 3.
-- In the second band, nodatavalue = 13, pixel value = 4
insert into dummy_rast values(
1,
(
'01' -- little endian (uint8 ndr)
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'0000' -- version (uint16 0)
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'0200' -- nBands (uint16 0)
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'17263529ED684A3F' -- scaleX (float64 0.000805965234044584)
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'F9253529ED684ABF' -- scaleY (float64 -0.00080596523404458)
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'1C9F33CE69E352C0' -- ipX (float64 -75.5533328537098)
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'718F0E9A27A44840' -- ipY (float64 49.2824585505576)
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'ED50EB853EC32B3F' -- skewX (float64 0.000211812383858707)
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'7550EB853EC32B3F' -- skewY (float64 0.000211812383858704)
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'E6100000' -- SRID (int32 4326)
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'0100' -- width (uint16 1)
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'0100' -- height (uint16 1)
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'6' -- hasnodatavalue and isnodata value set to true.
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'2' -- first band type (4BUI)
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'03' -- novalue==3
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'03' -- pixel(0,0)==3 (same that nodata)
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'0' -- hasnodatavalue set to false
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'5' -- second band type (16BSI)
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'0D00' -- novalue==13
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'0400' -- pixel(0,0)==4
)::raster
);
select ST_BandIsNoData(rast, 1) from dummy_rast where rid = 1; -- Expected true
select ST_BandIsNoData(rast, 2) from dummy_rast where rid = 1; -- Expected false