GTiff -- GeoTIFF File Format

Most forms of TIFF and GeoTIFF files are supported by GDAL for reading, and somewhat less varieties can be written.

When built with internal libtiff or with libtiff >= 4.0, GDAL also supports reading and writing BigTIFF files (evolution of the TIFF format to support files larger than 4 GB).

Currently band types of Byte, UInt16, Int16, UInt32, Int32, Float32, Float64, CInt16, CInt32, CFloat32 and CFloat64 are supported for reading and writing. Paletted images will return palette information associated with the band. The compression formats listed below should be supported for reading as well.

As well, one bit files, and some other unusual formulations of GeoTIFF file, such as YCbCr color model files, are automatically translated into RGBA (red, green, blue, alpha) form, and treated as four eight bit bands.

Georeferencing

Most GeoTIFF projections should be supported, with the caveat that in order to translate uncommon Projected, and Geographic coordinate systems into OGC WKT it is necessary to have the EPSG .csv files available. They must be found at the location pointed to by the GEOTIFF_CSV environment variable.

Georeferencing from GeoTIFF is supported in the form of one tiepoint and pixel size, a transformation matrix, or a list of GCPs.

If no georeferencing information is available in the TIFF file itself, GDAL will also check for, and use an ESRI world file with the extension .tfw, .tifw/.tiffw or .wld, as well as a MapInfo .tab file.

GDAL can read and write the RPCCoefficientTag as described in the RPCs in GeoTIFF proposed extension. The tag is written only for files created with the default profile GDALGeoTIFF. For other profiles, a .RPB file is created. In GDAL data model, the RPC coefficients are stored into the RPC metadata domain. For more details, see the RPC Georeferencing RFC. If .RPB or _RPC.TXT files are found, they will be used to read the RPCs, even if the RPCCoefficientTag tag is set.

Internal nodata masks

(from GDAL 1.6.0)

TIFF files can contain internal transparency masks. The GeoTIFF driver recognizes an internal directory as being a transparency mask when the FILETYPE_MASK bit value is set on the TIFFTAG_SUBFILETYPE tag. According to the TIFF specification, such internal transparency masks contain 1 sample of 1-bit data. Although the TIFF specification allows for higher resolutions for the internal transparency mask, the GeoTIFF driver only supports internal transparency masks of the same dimensions as the main image. Transparency masks of internal overviews are also supported.

When the GDAL_TIFF_INTERNAL_MASK configuration option is set to YES and the GeoTIFF file is opened in update mode, the CreateMaskBand() method on a TIFF dataset or rasterband will create an internal transparency mask. Otherwise, the default behaviour of nodata mask creation will be used, that is to say the creation of a .msk file, as per RFC 15

Starting with GDAL 1.8.0, 1-bit internal mask band are deflate compressed. When reading them back, to make conversion between mask band and alpha band easier, mask bands are exposed to the user as being promoted to full 8 bits (i.e. the value for unmasked pixels is 255) unless the GDAL_TIFF_INTERNAL_MASK_TO_8BIT configuration option is set to NO. This does not affect the way the mask band is written (it is always 1-bit).

Overviews

The GeoTIFF driver supports reading, creation and update of internal overviews. Internal overviews can be created on GeoTIFF files opened in update mode (with gdaladdo for instance). If the GeoTIFF file is opened as read only, the creation of overviews will be done in an external .ovr file. Overview are only updated on request with the BuildOverviews() method.

(From GDAL 1.6.0) If a GeoTIFF file has a transparency mask and the GDAL_TIFF_INTERNAL_MASK environment variable is set to YES and the GeoTIFF file is opened in update mode, BuildOverviews() will automatically create overviews for the internal transparency mask. These overviews will be refreshed by further calls to BuildOverviews() even if GDAL_TIFF_INTERNAL_MASK is not set to YES.

(From GDAL 1.8.0) The block size (tile width and height) used for overviews (internal or external) can be specified by setting the GDAL_TIFF_OVR_BLOCKSIZE environment variable to a power-of-two value between 64 and 4096. The default value is 128.

Metadata

GDAL can deal with the following baseline TIFF tags as dataset-level metadata :

The name of the metadata item to use is one of the above names ("TIFFTAG_DOCUMENTNAME", ...).

Other non standard metadata items can be stored in a TIFF file created with the profile GDALGeoTIFF (the default, see below in the Creation issues section). Those metadata items are grouped together into a XML string stored in the non standard TIFFTAG_GDAL_METADATA ASCII tag (code 42112). When BASELINE or GeoTIFF profile are used, those non standard metadata items are stored into a PAM .aux.xml file.

The value of GDALMD_AREA_OR_POINT ("AREA_OR_POINT") metadata item is stored in the GeoTIFF key RasterPixelIsPoint for GDALGeoTIFF or GeoTIFF profiles.

Starting with GDAL 1.9.0, XMP metadata can be extracted from the file, and will be stored as XML raw content in the xml:XMP metadata domain.

Starting with GDAL 1.10, EXIF metadata can be extracted from the file, and will be stored the EXIF metadata domain.

Color Profile Metadata

Starting with GDAL 1.11, GDAL can deal with the following color profile metadata in the COLOR_PROFILE domain:

Note that these metadata properties can only be used on the original raw pixel data. If automatic conversion to RGB has been done, the color profile information cannot be used.

All these metadata tags can be overriden and/or used as creation options.

Nodata value

GDAL stores band nodata value in the non standard TIFFTAG_GDAL_NODATA ASCII tag (code 42113) for files created with the default profile GDALGeoTIFF. Note that all bands must use the same nodata value. When BASELINE or GeoTIFF profile are used, the nodata value is stored into a PAM .aux.xml file.

Open options

Creation Issues

GeoTIFF files can be created with any GDAL defined band type, including the complex types. Created files may have any number of bands. Files with exactly 3 bands will be given a photometric interpretation of RGB, files with exactly four bands will have a photometric interpretation of RGBA, while all other combinations will have a photometric interpretation of MIN_IS_WHITE. Files with pseudo-color tables, or GCPs can currently only be created when creating from an existing GDAL dataset with those objects (GDALDriver::CreateCopy()).

Note that the GeoTIFF format does not support parametric description of datums, so TOWGS84 parameters in coordinate systems are lost in GeoTIFF format.

Creation Options

About JPEG compression of RGB images

When translating a RGB image to JPEG-In-TIFF, using PHOTOMETRIC=YCBCR can make the size of the image typically 2 to 3 times smaller than the default photometric value (RGB). When using PHOTOMETRIC=YCBCR, the INTERLEAVE option must be kept to its default value (PIXEL), otherwise libtiff will fail to compress the data.

Note also that the dimensions of the tiles or strips must be a multiple of 8 for PHOTOMETRIC=RGB or 16 for PHOTOMETRIC=YCBCR

Streaming operations

Starting with GDAL 2.0, the GeoTIFF driver can support reading or writing TIFF files (with some restrictions detailed below) in a streaming compatible way.

When reading a file from /vsistdin/, a named pipe (on Unix), or if forcing streamed reading by setting the TIFF_READ_STREAMING configuration option to YES, the GeoTIFF driver will assume that the TIFF Image File Directory (IFD) is at the beginning of the file, i.e. at offset 8 for a classical TIFF file or at offset 16 for a BigTIFF file. The values of the tags of array type must be contained at the beginning of file, after the end of the IFD and before the first image strip/tile. The reader must read the strips/tiles in the order they are written in the file. For a pixel interleaved file (PlanarConfiguration=Contig), the recommended order for a writer, and thus for a reader, is from top to bottom for a strip-organized file or from top to bottom, which a chunk of a block height, and left to right for a tile-organized file. For a band organized file (PlanarConfiguration=Separate), the above order is recommended with the content of the first band, then the content of the second band, etc... Technically this order corresponds to increasing offsets in the TileOffsets/StripOffsets tag. This is the order that the GDAL raster copy routine will assume.

If the order is not the one described above, the UNORDERED_BLOCKS=YES dataset metadata item will be set in the TIFF metadata domain. Each block offset can be determined by querying the "BLOCK_OFFSET_[xblock]_[yblock]" band metadata items in the TIFF metadata domain (where xblock, yblock is the coordinate of the block), and a reader could use that information to determine the appropriate reading order for image blocks.

The files that are streamed into the GeoTIFF driver may be compressed, even if the GeoTIFF driver cannot produce such files in streamable output mode (regular creation of TIFF files will produce such compatible files for streamed reading).

When writing a file to /vsistdout/, a named pipe (on Unix), or when definiting the STREAMABLE_OUTPUT=YES creation option, the CreateCopy() method of the GeoTIFF driver will generate a file with the above defined constraints (related to position of IFD and block order), and this is only supported for a uncompressed file. The Create() method also supports creating streamable compatible files, but the writer must be careful to set the projection, geotransform or metadata before writting image blocks (so that the IFD is written at the beginning of the file). And when writing image blocks, the order of blocks must be the one of the above paragraph, otherwise errors will be reported.

Some examples :

gdal_translate in.tif /vsistdout/ -co TILED=YES | gzip | gunzip | gdal_translate /vsistdin/ out.tif -co TILED=YES -co COMPRESS=DEFLATE
or
mkfifo my_fifo
gdalwarp in.tif my_fifo -t_srs EPSG:3857
gdal_translate my_fifo out.png -of PNG

Note: not all utilities are compatible with such input or output streaming operations, and even those which may deal with such files may not manage to deal with them in all circumstances, for example if the reading driver drived by the output file is not compatible with the block order of the streamed input.

Configuration options

This paragraph lists the configuration options that can be set to alter the default behaviour of the GTiff driver.


See Also: