# MFF2 -- Vexcel MFF2 Image

GDAL supports MFF2 Image raster file format for read, update, and creation. The MFF2 (Multi-File Format 2) format was designed to fit into Vexcel Hierarchical Key-Value (HKV) databases, which can store binary data as well as ASCII parameters. This format is primarily used internally to the Vexcel InSAR processing system.

To select an MFF2 dataset, select the directory containing the `attrib`, and `image_data` files for the dataset.

Currently only latitude/longitude and UTM projection are supported (georef.projection.name = ll or georef.projection.name = utm), with the affine transform computed from the lat/long control points. In any event, if GCPs are available in a georef file, they are returned with the dataset.

Newly created files (with a type of `MFF2`) are always just raw rasters with no georeferencing information. For read, and creation all data types (real, integer and complex in bit depths of 8, 16, 32) should be supported.

IMPORTANT: When creating a new MFF2, be sure to set the projection before setting the geotransform (this is necessary because the geotransform is stored internally as 5 latitude-longitude ground control points, and the projection is needed to do the conversion).

NOTE: Implemented as `gdal/frmts/raw/hkvdataset.cpp`.

## Format Details

### MFF2 Top-level Structure

An MFF2 "file" is actually a set of files stored in a directory containing an ASCII header file entitled "attrib", and binary image data entitled "image_data". Optionally, there may be an ASCII "georef" file containing georeferencing and projection information, and an "image_data_ovr" (for "image_data" binary image data) file containing tiled overviews of the image in TIFF format. The ASCII files are arranged in key=value pairs. The allowable pairs for each file are described below.

### The "attrib" File

As a minimum, the "attrib" file must specify the image extents, pixel size in bytes, pixel encoding and datatype, and pixel byte order. For example,

    extent.cols    = 800
    extent.rows    = 1040
    pixel.size     = 32
    pixel.encoding = { unsigned twos_complement *ieee_754 }
    pixel.field    = { *real complex }
    pixel.order    = { lsbf *msbf }
    version        = 1.1

specifies an image that is 1040 lines by 800 pixels in extent. The pixels are 32 bits of real data in "most significant byte first" (msbf) order, encoded according to the ieee_754 specification. In MFF2, when a value must belong to a certain subset (eg. pixel.order must be either lsbf or msbf), all options are displayed between curly brackets, and the one appropriate for the current file is indicated with a "*".

The file may also contain the following lines indicating the number of channels of data, and how they are interleaved within the binary data file.

    channel.enumeration = 1
    channel.interleave = { *pixel tile sequential }

### The "image_data" File

The "image_data" file consists of raw binary data, with extents, pixel encoding, and number of channels as indicated in the "attrib" file.

### The "georef" File

The "georef" file is used to describe the geocoding and projection information for the binary data. For example,

    top_left.latitude            = 32.93333333333334
    top_left.longitude           = 130.0
    top_right.latitude           = 32.93333333333334
    top_right.longitude          = 130.5
    bottom_left.latitude         = 32.50000000000001
    bottom_left.longitude        = 130.0
    bottom_right.latitude        = 32.50000000000001
    bottom_right.longitude       = 130.5
    centre.latitude              = 32.71666666666668
    centre.longitude             = 130.25
    projection.origin_longitude  = 0
    projection.name              = ll
    spheroid.name                = wgs-84

describes an orthogonal latitude/longitude (ll) projected image, with latitudes and longitudes based on the wgs-84 ellipsoid.

Since MFF2 version 1.1, top_left refers to the top left corner of the top left pixel. top_right refers to the top right corner of the top right pixel. bottom_left refers to the bottom left corner of the bottom left pixel. bottom_right refers to the bottom right corner of the bottom right pixel. centre refers to the centre of the four corners defined above (center of the image).

Mathematically, for an Npix by Nline image, the corners and centre in (pixel,line) coordinates for MFF2 version 1.1 are:

    top_left: (0,0)
    top_right: (Npix,0)
    bottom_left: (0,Nline)
    bottom_right: (Npix,Nline)
    centre: (Npix/2.0,Nline/2.0)

These calculations are done using floating point arithmetic (ie. centre coordinates may take on non-integer values).

Note that the corners are always expressed in latitudes/longitudes, even for projected images.

### Supported projections

ll- Orthogonal latitude/longitude projected image, with latitude parallel to the rows, longitude parallel to the columns. Parameters: spheroid name, projection.origin_longitude (longitude at the origin of the projection coordinates). If not set, this should default to the central longitude of the output image based on its projection boundaries.

utm- Universal Transverse Mercator projected image. Parameters: spheroid name, projection.origin_longitude (central meridian for the utm projection). The central meridian must be the meridian at the centre of a UTM zone, ie. 3 degrees, 9 degrees, 12 degrees, etc. If this is not specified or set a valid UTM central meridian, the reader should reset the value to the nearest valid central meridian based on the central longitude of the output image. The latitude at the origin of the UTM projection is always 0 degrees.

### Recognized ellipsoids

MFF2 format associates the following names with ellipsoid equatorial radius and inverse flattening parameters:

    airy-18304:            6377563.396      299.3249646
    modified-airy4:        6377340.189      299.3249646
    australian-national4:  6378160          298.25
    bessel-1841-namibia4:  6377483.865      299.1528128
    bessel-18414:          6377397.155      299.1528128
    clarke-18584:          6378294.0        294.297
    clarke-18664:          6378206.4        294.9786982
    clarke-18804:          6378249.145      293.465
    everest-india-18304:   6377276.345      300.8017
    everest-sabah-sarawak4:6377298.556      300.8017
    everest-india-19564:   6377301.243      300.8017
    everest-malaysia-19694:6377295.664      300.8017
    everest-malay-sing4:   6377304.063      300.8017
    everest-pakistan4:     6377309.613      300.8017
    modified-fisher-19604: 6378155          298.3
    helmert-19064:         6378200          298.3
    hough-19604:           6378270          297
    hughes4:               6378273.0        298.279
    indonesian-1974:       6378160          298.247
    international-1924:    6378388          297
    iugc-67:               6378160.0        298.254
    iugc-75:               6378140.0        298.25298
    krassovsky-1940:       6378245          298.3
    kaula:                 6378165.0        292.308
    grs-80:                6378137          298.257222101
    south-american-1969:   6378160          298.25
    wgs-72:                6378135          298.26
    wgs-84:                6378137          298.257223563
    ev-wgs-84:             6378137          298.252841
    ev-bessel:             6377397          299.1976073

### Explanation of fields

    channel.enumeration:  (optional- only needed for multiband)
    Number of channels of data (eg. 3 for rgb)

    channel.interleave = { *pixel tile sequential } :  (optional- only
    needed for multiband)

    For multiband data, indicates how the channels are interleaved.  *pixel
    indicates that data is stored red value, green value, blue value, red
    value, green value, blue value etc. as opposed to (line of red values)
    (line of green values) (line of blue values) or (entire red channel)
    (entire green channel) (entire blue channel)

    extent.cols:
    Number of columns of data.

    extent.rows:
    Number of rows of data.

    pixel.encoding = { *unsigned twos-complement ieee-754 }:
    Combines with pixel.size and pixel.field to give the data type:
    (encoding, field, size)- type
    (unsigned, real, 8)- unsigned byte data
    (unsigned, real, 16)- unsigned int 16 data
    (unsigned, real, 32)- unsigned int 32 data
    (twos-complement, real, 16)- signed int 16 data
    (twos-complement, real, 32)- signed int 32 data
    (twos-complement, complex, 64)- complex signed int 32 data
    (ieee-754, real, 32)- real 32 bit floating point data
    (ieee-754, real, 64)- real 64 bit floating point data
    (ieee-754, complex, 64)- complex 32 bit floating point data
    (ieee-754, complex, 128)- complex 64 bit floating point data

    pixel.size:
    Size of one pixel of one channel (bits).

    pixel.field = { *real complex }:
    Whether the data is real or complex.

    pixel.order = { *lsbf msbf }:
    Byte ordering of the data (least or most significant byte first).

    version: (only in newer versions- if not present, older version is
    assumed) Version of mff2.