Supported Raster File Formats and Their Configuration

In this section, the EOxServer’s handling of raster file formats and OWS service specific format configuration is described.

Format Registry

The format registry is the list of raster file formats recognised by EOxServer. It holds definitions of both input and output formats. Each format record defines the MIME-type (unique, primary key), library, driver, and the default file extension.

Currently, EOxServer handles the raster data exclusively by means of the GDAL library. Thus, in principle, any raster file format supported by the GDAL library is supported by EOxServer. In particular, any raster file format readable by the GDAL library (provided that the file structure can be decomposed to one single-type, single- or multi-band image) can be used as the input and, vice versa, any raster file format writeable by the GDAL library can used as the output produced by WCS and WMS services.

Any raster file format intended to be used by EOxServer must be defined in the format registry. The format registry then provides unique mappings from MIME-type to the (GDAL) format driver.

Format Configuration

The format registry configuration is split in two parts (files):

  • per-installation (mandatory) format configuration (set up automatically during the EOxServer installation) defining the default baseline set of formats (<instal.path>/eoxserver/conf/default_formats.conf).

  • per-instance (optional) format configuration allowing customization of the format registry (<instance path>/conf/formats.conf).

In case of conflicting format definitions, the per-instance configuration takes precedence. Both formats’ configuration files share the same text file format.

The formats’ configuration is a simple text file containing a simple list of format definitions. One format definition (record) per line. Each record is then a comma separated list of the following text fields:

<MIME-type>, <driver>, <file extension>

The mime type is used as the primary key and thus any repeated MIME-type will rewrite the previous format definition(s) using this MIME-type. The driver field should be in format GDAL/<GDAL driver name>. To list available drivers provided by your GDAL installation use the following command:

::

gdalinfo –formats

The GDAL prefix is used as place-holder to allow future use of additional library back-ends. The file extension shall be written including the separating dot .. Any leading or trailing white-characters as well as empty lines are ignored. The # character is used as line-comment and any content between this character and the end of the line is ignored.

An example format definition:

image/tiff,GDAL/GTiff,.tif # GeoTIFF raster file format

Since the list of supported drivers may vary for different installations of the back-end (GDAL) library, the library drivers are checked by EOxServer ignoring any format definitions requiring non-supported library drivers. Any invalid format record is reported to the EOxServer log. Further, EOxServer checks automatically which of the library drivers are ‘read-only’, i.e., which cannot be used to produce output images, and restricts these to be used for data input only.

Web Coverage Service - Format Configuration

The list of the file formats supported by the Web Coverage Service (WCS) is specified in the EOxServer configuration (<instance path>/conf/eoxserver.conf) in the section serices.ows.wcs:

[services.ows.wcs]
supported_formats=<MIME type>[,<MIME type>[,<MIME type> ... ]]

The supported WCS formats are specified as a comma-separated list of MIME-types. The listed MIME-types must be defined in the format registry otherwise they will be ignored. Read-only file formats will also be ignored.

The supported formats are announced through the WCS Capabilities and CoverageDescription (the output may vary based on the WCS version used). The use of in invalid MIME-types (not listed among the supported formats) in getCoverge() requests will lead to errors (OWS Exceptions).

Web Coverage Service - Native Format Configuration

The native format (as defined by WCS 2.0.1 [OGC 09-110r4]) is the default raster file format returned by the getCoverage() operation in case of a missing explicit format specification. By default, EOxServer sets the native format to the format of the stored source data (source format), however, in cases when the source format cannot be used (‘read-only’ source format) and/or another default format is desired, EOxServer allows the configuration of WCS native formats (<instance path>/conf/eoxserver.conf, section services.ows.wcs20):

[services.ows.wcs20]
default_native_format=<MIME-type>
source_to_native_format_map=[<src.MIME-type,native-MIME-type>[,<src.MIME-type,native-MIME-type> ... ]]

The default native format option is used in cases when the source format cannot be used (read-only) and no source to native format mapping is present. This option must always be set to a valid format (GeoTIFF by default). The source to native format mapping, as the name suggests, maps the (zero, one, or more) source format(s) to non-default native formats. The source formats are not restricted to the read-only ones. This option accepts a comma-separated list of MIME-type pairs.

Web Map Service - Format Configuration

The list of the file formats supported by the Web Map Service’s (WMS) getMap() operation is specified in the EOxServer configuration (<instance path>/conf/eoxserver.conf) in section serices.ows.wms:

[services.ows.wms]
supported_formats=<MIME type>[,<MIME type>[,<MIME type> ... ]]

The supported WMS formats are specified as a comma-separated list of MIME-types. The listed MIME-types must be defined in the format registry otherwise they will be ignored. The read-only file formats will be ignored.

The supported formats are announced through the WMS Capabilities (the output may vary based on the WMS version used).

References

[OGC 09-110r4]

http://www.opengeospatial.org/standards/wcs