# DERIVED -- Derived subdatasets driver

This driver allows to access to subdatasets derived from a given dataset. Those derived datasets have the same projection reference, geo-transform and metadata than the original dataset, but derives new pixel values using gdal pixel functions.

## Available functions

Available derived datasets are:

- AMPLITUDE: Amplitude of pixels from input bands
- PHASE: Phase of pixels from input bands
- REAL: Real part of pixels from input bands
- IMAG: Imaginary part of pixels from input bands
- CONJ: Conjugate of pixels from input bands
- INTENSITY: Intensity (squared amplitude) of pixels from input bands
- LOGAMPLITUDE: Log10 of amplitude of pixels from input bands

A typical use is to directly access amplitude, phase or log-amplitude of any complex dataset.

## Accessing derived subdatasets

Derived subdatasets are stored in the DERIVED_SUBDATASETS metadata domain, and can be accessed using the following syntax:

      DERIVED_SUBDATASET:FUNCTION:dataset_name

where function is one of AMPLITUDE, PHASE, REAL, IMAG, CONJ, INTENSITY, LOGAMPLITUDE. So as to ensure numerical precision, all derived subdatasets bands will have Float64 or CFloat64 precision (depending on the function used).

For instance:

      $ gdalinfo cint_sar.tif

    Driver: GTiff/GeoTIFF
    Files: cint_sar.tif
    Size is 5, 6
    Coordinate System is `'
    GCP Projection =
    GEOGCS["WGS 84",
        DATUM["WGS_1984",
            SPHEROID["WGS 84",6378137,298.257223563,
                AUTHORITY["EPSG","7030"]],
            AUTHORITY["EPSG","6326"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4326"]]
    GCP[  0]: Id=1, Info=
              (-1910.5,-7430.5) -> (297.507,16.368,0)
    GCP[  1]: Id=2, Info=
              (588.5,-7430.5) -> (297.938,16.455,0)
    GCP[  2]: Id=3, Info=
              (588.5,7363.5) -> (297.824,16.977,0)
    GCP[  3]: Id=4, Info=
              (-1910.5,7363.5) -> (297.393,16.89,0)
    Metadata:
      AREA_OR_POINT=Area
      CEOS_ACQUISITION_TIME=19970718024119087
      CEOS_ELLIPSOID=GEM6
      CEOS_INC_ANGLE=24.824
      CEOS_LINE_SPACING_METERS=3.9900000
      CEOS_LOGICAL_VOLUME_ID=0001667400297672
      CEOS_PIXEL_SPACING_METERS=7.9040000
      CEOS_PIXEL_TIME_DIR=INCREASE
      CEOS_PLATFORM_HEADING=347.339
      CEOS_PLATFORM_LATITUDE=16.213
      CEOS_PLATFORM_LONGITUDE=-65.311
      CEOS_PROCESSING_AGENCY=ESA
      CEOS_PROCESSING_COUNTRY=ITALY
      CEOS_PROCESSING_FACILITY=ES
      CEOS_SEMI_MAJOR=6378.1440000
      CEOS_SEMI_MINOR=6356.7590000
      CEOS_SENSOR_CLOCK_ANGLE=90.000
      CEOS_SOFTWARE_ID=ERS2-SLC-6.1
      CEOS_TRUE_HEADING=345.5885834
    Image Structure Metadata:
      INTERLEAVE=BAND
    Corner Coordinates:
    Upper Left  (    0.0,    0.0)
    Lower Left  (    0.0,    6.0)
    Upper Right (    5.0,    0.0)
    Lower Right (    5.0,    6.0)
    Center      (    2.5,    3.0)
    Band 1 Block=5x6 Type=CInt16, ColorInterp=Gray

      $ gdalinfo DERIVED_SUBDATASET:LOGAMPLITUDE:cint_sar.tif

    Driver: DERIVED/Derived datasets using VRT pixel functions
    Files: cint_sar.tif
    Size is 5, 6
    Coordinate System is `'
    GCP Projection =
    GEOGCS["WGS 84",
        DATUM["WGS_1984",
            SPHEROID["WGS 84",6378137,298.257223563,
                AUTHORITY["EPSG","7030"]],
            AUTHORITY["EPSG","6326"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4326"]]
    GCP[  0]: Id=1, Info=
              (-1910.5,-7430.5) -> (297.507,16.368,0)
    GCP[  1]: Id=2, Info=
              (588.5,-7430.5) -> (297.938,16.455,0)
    GCP[  2]: Id=3, Info=
              (588.5,7363.5) -> (297.824,16.977,0)
    GCP[  3]: Id=4, Info=
              (-1910.5,7363.5) -> (297.393,16.89,0)
    Metadata:
      AREA_OR_POINT=Area
      CEOS_ACQUISITION_TIME=19970718024119087
      CEOS_ELLIPSOID=GEM6
      CEOS_INC_ANGLE=24.824
      CEOS_LINE_SPACING_METERS=3.9900000
      CEOS_LOGICAL_VOLUME_ID=0001667400297672
      CEOS_PIXEL_SPACING_METERS=7.9040000
      CEOS_PIXEL_TIME_DIR=INCREASE
      CEOS_PLATFORM_HEADING=347.339
      CEOS_PLATFORM_LATITUDE=16.213
      CEOS_PLATFORM_LONGITUDE=-65.311
      CEOS_PROCESSING_AGENCY=ESA
      CEOS_PROCESSING_COUNTRY=ITALY
      CEOS_PROCESSING_FACILITY=ES
      CEOS_SEMI_MAJOR=6378.1440000
      CEOS_SEMI_MINOR=6356.7590000
      CEOS_SENSOR_CLOCK_ANGLE=90.000
      CEOS_SOFTWARE_ID=ERS2-SLC-6.1
      CEOS_TRUE_HEADING=345.5885834
    Corner Coordinates:
    Upper Left  (    0.0,    0.0)
    Lower Left  (    0.0,    6.0)
    Upper Right (    5.0,    0.0)
    Lower Right (    5.0,    6.0)
    Center      (    2.5,    3.0)
    Band 1 Block=5x6 Type=Float64, ColorInterp=Undefined

## Listing available subdatasets

Available subdatasets are reported in the DERIVED_SUBDATASETS metadata domain. Only functions that make sense will be reported for a given dataset, which means that AMPLITUDE, PHASE, REAL, IMAG, CONJ and INTENSITY will only be reported if the dataset has at least one complex band. Nevertheless, even if not reported, those derived datasets are still reachable with the syntax presented above.

        $ gdalinfo -mdd DERIVED_SUBDATASETS cint_sar.tif

    Driver: GTiff/GeoTIFF
    Files: cint_sar.tif
    Size is 5, 6
    Coordinate System is `'
    GCP Projection =
    GEOGCS["WGS 84",
        DATUM["WGS_1984",
            SPHEROID["WGS 84",6378137,298.257223563,
                AUTHORITY["EPSG","7030"]],
            AUTHORITY["EPSG","6326"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4326"]]
    GCP[  0]: Id=1, Info=
              (-1910.5,-7430.5) -> (297.507,16.368,0)
    GCP[  1]: Id=2, Info=
              (588.5,-7430.5) -> (297.938,16.455,0)
    GCP[  2]: Id=3, Info=
              (588.5,7363.5) -> (297.824,16.977,0)
    GCP[  3]: Id=4, Info=
              (-1910.5,7363.5) -> (297.393,16.89,0)
    Metadata:
      AREA_OR_POINT=Area
      CEOS_ACQUISITION_TIME=19970718024119087
      CEOS_ELLIPSOID=GEM6
      CEOS_INC_ANGLE=24.824
      CEOS_LINE_SPACING_METERS=3.9900000
      CEOS_LOGICAL_VOLUME_ID=0001667400297672
      CEOS_PIXEL_SPACING_METERS=7.9040000
      CEOS_PIXEL_TIME_DIR=INCREASE
      CEOS_PLATFORM_HEADING=347.339
      CEOS_PLATFORM_LATITUDE=16.213
      CEOS_PLATFORM_LONGITUDE=-65.311
      CEOS_PROCESSING_AGENCY=ESA
      CEOS_PROCESSING_COUNTRY=ITALY
      CEOS_PROCESSING_FACILITY=ES
      CEOS_SEMI_MAJOR=6378.1440000
      CEOS_SEMI_MINOR=6356.7590000
      CEOS_SENSOR_CLOCK_ANGLE=90.000
      CEOS_SOFTWARE_ID=ERS2-SLC-6.1
      CEOS_TRUE_HEADING=345.5885834
    Metadata (DERIVED_SUBDATASETS):
      DERIVED_SUBDATASET_0_NAME=DERIVED_SUBDATASET:AMPLITUDE:cint_sar.tif
      DERIVED_SUBDATASET_0_DESC=Amplitude of input bands from cint_sar.tif
      DERIVED_SUBDATASET_1_NAME=DERIVED_SUBDATASET:PHASE:cint_sar.tif
      DERIVED_SUBDATASET_1_DESC=Phase of input bands from cint_sar.tif
      DERIVED_SUBDATASET_2_NAME=DERIVED_SUBDATASET:REAL:cint_sar.tif
      DERIVED_SUBDATASET_2_DESC=Real part of input bands from cint_sar.tif
      DERIVED_SUBDATASET_3_NAME=DERIVED_SUBDATASET:IMAG:cint_sar.tif
      DERIVED_SUBDATASET_3_DESC=Imaginary part of input bands from cint_sar.tif
      DERIVED_SUBDATASET_4_NAME=DERIVED_SUBDATASET:CONJ:cint_sar.tif
      DERIVED_SUBDATASET_4_DESC=Conjugate of input bands from cint_sar.tif
      DERIVED_SUBDATASET_5_NAME=DERIVED_SUBDATASET:INTENSITY:cint_sar.tif
      DERIVED_SUBDATASET_5_DESC=Intensity (squared amplitude) of input bands from cint_sar.tif
      DERIVED_SUBDATASET_6_NAME=DERIVED_SUBDATASET:LOGAMPLITUDE:cint_sar.tif
      DERIVED_SUBDATASET_6_DESC=log10 of amplitude of input bands from cint_sar.tif
    Image Structure Metadata:
      INTERLEAVE=BAND
    Corner Coordinates:
    Upper Left  (    0.0,    0.0)
    Lower Left  (    0.0,    6.0)
    Upper Right (    5.0,    0.0)
    Lower Right (    5.0,    6.0)
    Center      (    2.5,    3.0)
    Band 1 Block=5x6 Type=CInt16, ColorInterp=Gray

## See Also:

- Using Derived Bands part of the GDAL VRT tutorial