ST_Value
이전  11.6. 래스터 픽셀 접근자 및 설정자(setter)  다음

제목

ST_Value — 입력 columnx, rowy 픽셀의 입력 밴드의 값, 또는 특정 기하학적 포인트의 밴드의 값을 반환합니다. 밴드 번호는 1부터 시작하며, 따로 지정하지 않을 경우 1로 가정합니다. exclude_nodata_value 를 거짓으로 설정할 경우, nodata 픽셀을 포함한 모든 픽셀이 교차한다고 가정하고 값을 반환합니다. exclude_nodata_value 를 설정하지 않은 경우, 래스터의 메타데이터에서 값을 읽어 들입니다.

요약

double precision ST_Value(raster rast, geometry pt, boolean exclude_nodata_value=true);

double precision ST_Value(raster rast, integer band, geometry pt, boolean exclude_nodata_value=true, text resample='nearest');

double precision ST_Value(raster rast, integer x, integer y, boolean exclude_nodata_value=true);

double precision ST_Value(raster rast, integer band, integer x, integer y, boolean exclude_nodata_value=true);

Description

입력한 columnx, rowy 픽셀 또는 특정 도형과 교차하는 픽셀들의 위치의 밴드 값을 설정해서 나온 수정된 래스터를 반환합니다. 밴드 번호는 1부터 시작하며, 따로 설정하지 않을 경우 1로 가정합니다.

exclude_nodata_value 를 참으로 설정할 경우, 래스터의 nodata 값이 아닌 픽셀의 개수만 반환할 것입니다. 모든 픽셀의 개수를 구하려면 exclude_nodata_value 를 거짓으로 설정하십시오.

The allowed values of the resample parameter are "nearest" which performs the default nearest-neighbor resampling, "bilinear" which performs a bilinear interpolation to estimate the value between pixel centers, and the nearest-neighbor boundary options "nearest-UL", "nearest-UR", "nearest-LL", and "nearest-LR". Boundary options choose which pixel is returned when the point lies on a horizontal or vertical pixel boundary, including corner intersections.

Enhanced: 3.7.0 resample accepts nearest-neighbor boundary options "nearest-UL", "nearest-UR", "nearest-LL", and "nearest-LR".

개선 사항: 2.1.0 버전부터 선택적인 exclude_nodata_value 인수를 추가했습니다.

개선 사항: 2.0.0 버전부터 선택적인 exclude_nodata_value 인수를 추가했습니다.

예시

Get raster values at particular postgis geometry points. The srid of your geometry should be same as for your raster.

Code
SELECT rid, ST_Value(rast, foo.pt_geom) As b1pval, ST_Value(rast, 2, foo.pt_geom) As b2pval
FROM dummy_rast CROSS JOIN (SELECT ST_SetSRID(ST_Point(3427927.77, 5793243.76), 0) As pt_geom) As foo
WHERE rid=2;
래스터 출력
rid | b1pval | b2pval
-----+--------+--------
   2 |    252 |     79

General fictitious example using a real table.

Code
SELECT rid, ST_Value(rast, 3, sometable.geom) As b3pval
FROM sometable
WHERE ST_Intersects(rast, sometable.geom);
Code
SELECT rid, ST_Value(rast, 1, 1, 1) As b1pval,
    ST_Value(rast, 2, 1, 1) As b2pval, ST_Value(rast, 3, 1, 1) As b3pval
FROM dummy_rast
WHERE rid=2;
래스터 출력
rid | b1pval | b2pval | b3pval
-----+--------+--------+--------
   2 |    253 |     78 |     70

Get all values in bands 1,2,3 of each pixel.

Code

SELECT x, y, ST_Value(rast, 1, x, y) As b1val,
    ST_Value(rast, 2, x, y) As b2val, ST_Value(rast, 3, x, y) As b3val
FROM dummy_rast CROSS JOIN
generate_series(1, 1000) As x CROSS JOIN generate_series(1, 1000) As y
WHERE rid =  2 AND x <= ST_Width(rast) AND y <= ST_Height(rast);
래스터 출력
 x | y | b1val | b2val | b3val
---+---+-------+-------+-------
 1 | 1 |   253 |    78 |    70
 1 | 2 |   253 |    96 |    80
 1 | 3 |   250 |    99 |    90
 1 | 4 |   251 |    89 |    77
 1 | 5 |   252 |    79 |    62
 2 | 1 |   254 |    98 |    86
 2 | 2 |   254 |   118 |   108
 :
 :

Get all values in bands 1,2,3 of each pixel same as above but returning the upper left point point of each pixel.

Code

SELECT ST_SetSRID(ST_Point(ST_UpperLeftX(rast) + ST_ScaleX(rast)*x,
        ST_UpperLeftY(rast) + ST_ScaleY(rast)*y),
        ST_SRID(rast)) As uplpt,
    ST_Value(rast, 1, x, y) As b1val,
    ST_Value(rast, 2, x, y) As b2val, ST_Value(rast, 3, x, y) As b3val
FROM dummy_rast CROSS JOIN
generate_series(1,1000) As x CROSS JOIN generate_series(1,1000) As y
WHERE rid =  2 AND x <= ST_Width(rast) AND y <= ST_Height(rast);
래스터 출력
            uplpt            | b1val | b2val | b3val
-----------------------------+-------+-------+-------
 POINT(3427929.25 5793245.5) |   253 |    78 |    70
 POINT(3427929.25 5793247)   |   253 |    96 |    80
 POINT(3427929.25 5793248.5) |   250 |    99 |    90
:

Get a polygon formed by union of all pixels that fall in a particular value range and intersect a particular polygon.

Code

SELECT ST_Union(pixpolyg) As shadow
FROM (SELECT ST_Translate(ST_MakeEnvelope(ST_UpperLeftX(rast), ST_UpperLeftY(rast),
            ST_UpperLeftX(rast) + ST_ScaleX(rast),
            ST_UpperLeftY(rast) + ST_ScaleY(rast), 0
            ), ST_ScaleX(rast)*x, ST_ScaleY(rast)*y
        ) As pixpolyg, ST_Value(rast, 2, x, y) As b2val
    FROM dummy_rast CROSS JOIN
generate_series(1,1000) As x CROSS JOIN generate_series(1,1000) As y
WHERE rid =  2
    AND x <= ST_Width(rast) AND y <= ST_Height(rast)) As foo
WHERE
    ST_Intersects(
        pixpolyg,
        ST_GeomFromText('POLYGON((3427928 5793244,3427927.75 5793243.75,3427928 5793243.75,3427928 5793244))',0)
        ) AND b2val != 254;
래스터 출력
        shadow
------------------------------------------------------------------------------------
 MULTIPOLYGON(((3427928 5793243.9,3427928 5793243.85,3427927.95 5793243.85,3427927.95 5793243.9,
 3427927.95 5793243.95,3427928 5793243.95,3427928.05 5793243.95,3427928.05 5793243.9,3427928 5793243.9)),((3427927.95 5793243.9,3427927.95 579324
3.85,3427927.9 5793243.85,3427927.85 5793243.85,3427927.85 5793243.9,3427927.9 5793243.9,3427927.9 5793243.95,
3427927.95 5793243.95,3427927.95 5793243.9)),((3427927.85 5793243.75,3427927.85 5793243.7,3427927.8 5793243.7,3427927.8 5793243.75,
3427927.8 5793243.8,3427927.8 5793243.85,3427927.85 5793243.85,3427927.85 5793243.8,3427927.85 5793243.75)),
((3427928.05 5793243.75,3427928.05 5793243.7,3427928 5793243.7,3427927.95 5793243.7,3427927.95 5793243.75,3427927.95 5793243.8,3427
927.95 5793243.85,3427928 5793243.85,3427928 5793243.8,3427928.05 5793243.8,
3427928.05 5793243.75)),((3427927.95 5793243.75,3427927.95 5793243.7,3427927.9 5793243.7,3427927.85 5793243.7,
3427927.85 5793243.75,3427927.85 5793243.8,3427927.85 5793243.85,3427927.9 5793243.85,
3427927.95 5793243.85,3427927.95 5793243.8,3427927.95 5793243.75)))

Checking all the pixels of a large raster tile can take a long time. You can dramatically improve speed at some lose of precision by orders of magnitude. By sampling pixels using the step optional parameter of generate_series. This next example does the same as previous but by checking 1 for every 4 (2x2) pixels and putting in the last checked. Putting in the checked pixel as the value for subsequent 4.

Code


SELECT ST_Union(pixpolyg) As shadow
FROM (SELECT ST_Translate(ST_MakeEnvelope(ST_UpperLeftX(rast), ST_UpperLeftY(rast),
            ST_UpperLeftX(rast) + ST_ScaleX(rast)*2,
            ST_UpperLeftY(rast) + ST_ScaleY(rast)*2, 0
            ), ST_ScaleX(rast)*x, ST_ScaleY(rast)*y
        ) As pixpolyg, ST_Value(rast, 2, x, y) As b2val
    FROM dummy_rast CROSS JOIN
generate_series(1,1000,2) As x CROSS JOIN generate_series(1,1000,2) As y
WHERE rid =  2
    AND x <= ST_Width(rast)  AND y <= ST_Height(rast)  ) As foo
WHERE
    ST_Intersects(
        pixpolyg,
        ST_GeomFromText('POLYGON((3427928 5793244,3427927.75 5793243.75,3427928 5793243.75,3427928 5793244))',0)
        ) AND b2val != 254;
래스터 출력
        shadow
------------------------------------------------------------------------------------
 MULTIPOLYGON(((3427927.9 5793243.85,3427927.8 5793243.85,3427927.8 5793243.95,
 3427927.9 5793243.95,3427928 5793243.95,3427928.1 5793243.95,3427928.1 5793243.85,3427928 5793243.85,3427927.9 5793243.85)),
 ((3427927.9 5793243.65,3427927.8 5793243.65,3427927.8 5793243.75,3427927.8 5793243.85,3427927.9 5793243.85,
 3427928 5793243.85,3427928 5793243.75,3427928.1 5793243.75,3427928.1 5793243.65,3427928 5793243.65,3427927.9 5793243.65)))