Satellite Import File Formats

The satellite import is file based. Satellite data is generally raster image based, but can differ in file format, number of channels (e.g. grayscale or color), geographic location etc.

Supported image formats:

• GeoTIFF with NinJo-specific additional meta data tags. GeoTIFF is a standard how to embed georeferencing metainformation in TIFF (Tagged Image File Format) raster images. NinJo requires some additional header tags in the private range.
• PNG with a NinJo-specific encoding of metadata in the free-text comment header
• JPEG with a NinJo-specific encoding of metadata in the free-text comment header
• XPIF – “Extended Processed Image File”, a native file format in the 2met! satellite reception software environment

GeoTIFF with NinJo-specific tags

TIFF (Tagged Image File Format) is a flexible file format for raster graphic files supporting multiple sub-files, tiling, different number of channels and color depths, compression type, etc. See the Wikipedia article “Tagged Image File Format” for an introduction and the TIFF format specification by Adobe for the full technical specification.

GeoTIFF is a metadata standard how to store georeferencing information about images in TIFF file headers.

NinJo expects several GeoTIFF and privately defined tags to be present in the import files in order to correctly georeference them and to assign satellite, product, color table information and so on.

Meaning of the “mandatory” column:

• x: These fields are necessary , ie non-optional
• 0: These fields are optional
• 1: These fields are alternative to be specified (either [m] or [°])
• 2: Second reference latitude eg for conical projections necessary
• 3: If earth is a sphere, then set earth_radius_a = earth_radius_b
• 4: Not necessary for equirectangular projection

GeoTIFF Tools

This section lists some freely available tools to display and manipulate GeoTIFF files.

• http://libtiff.org/ – libtiff. Library and command line tools to manipulate and dump information about TIFF files.
  • tiffinfo file.tif or tiffdump file.tif to dump TIFF metadata and to check if the NinJo tags are present
• http://geotiff.osgeo.org/ – libgeotiff. Library and command line tools to dump information about and manipulate GeoTIFF files
  • listgeo file.tiff to print the georeferencing information of a GeoTIFF file
• http://www.gdal.org/ – GDAL: Geospatial Data Abstraction Library. Library and command line tools to manipulate geospatial data in vector and raster formats and convert between them.

PNG with NinJo-specific metadata

PNG (Portable Network Graphics) is a file format for raster graphic files which supports different color depths, alpha (= transparency) channels and lossless compression. See the Wikipedia article “Portable Network Graphics” for an introduction and RFC 2083 for the full technical specification.

NinJo needs meta data to correctly georeference the image, assign satellite and product name, and so on. The PNG format allows for “text chunks” to be embedded in the image file. NinJo expects chunks tEXt or zTXt (Latin-1 encoded uncompressed or compressed) to be present with a Comment entry. The meta data is represented as key-value pairs in plain text format in a Comment entry.

See table Tags for PNG and JPEG files for a description of tag key names and values.

For 8-bit single-channel (grayscale) images it is possible to include a colortable mapping gray values to RGB colors and optionally a value table mapping the gray values to numbers or description texts inside the file. See section Embedded color and value tables. Alternatively a color table can also be provided as external configuration, see section External Color Table.

JPEG with NinJo-specific metadata

JPEG is a file format for raster graphic files with an effective, lossy compression and selectable compression-quality balance. See the Wikipedia article “JPEG” for an introduction and the JPEG Standard (JPEG ISO/IEC 10918-1 ITU-T Recommendation T.81) for the full technical specification.

NinJo needs meta data to correctly georeference the image, assign satellite and product name, and so on. The JPEG format allows for a free text comment to be embedded in the image file. The meta data is represented as key-value pairs in plain text format in the Comment entry.

See table Tags for PNG and JPEG files for a description of tag key names and values.

For 8-bit single-channel (grayscale) images it is possible to include a colortable mapping gray values to RGB colors and optionally a value table mapping the gray values to numbers or description texts inside the file. See section Embedded color and value tables. Alternatively a color table can also be provided as external configuration, see section External Color Table.

Tags for PNG and JPEG files

The format of the meta data comment is to combine each key and value with an equals sign between them in the format key=value. All key-value-pairs are concatenated in to a long string separated by semicolons in the format key1=value1;key2=value2.

Full example of a meta data comment entry:

VERSION=001;PIF_L=900;PIF_C=1400;PIF_NAV_FUNC=38;NAV_GOFF_LON=0;NAV_GOFF_LAT=0;TOP_LEFT_CORNER_LAT=69445;TOP_LEFT_CORNER_LON=-23960;BOT_RIGHT_CORNER_LAT=31512;BOT_RIGHT_CORNER_LON=35335;PIF_DAT_F=0;PIF_SRC_YEAR=2006;PIF_SRC_DAY=142;PIF_SRC_HOURS=1300;NINJO_SAT_NAME_ID=800014;NINJO_CHANNEL_ID=300015;

Meaning of the “mandatory” column:

• x: These fields are necessary , ie non-optional
• 0: Optional
• 4: Not necessary for equirectangular projection
• 5: Optional, only needed for the three given values. Else, the physical element is derived from the channel ID
• 6: Optional. These combinations can be set: Only COLORTABLE, or COLORTABLE and VALUETABLE_FLOAT, or COLORTABLE and VALUETABLE_STRING

Color and value tables

For 8-bit single-channel (grayscale) images it is possible to include inside the file meta data a colortable, which maps gray values to RGB colors, and optionally a value table, which maps the gray values to numbers or description texts.

To embed a color table inside the image, the tag COLORTABLE must be set. It maps each grayscale value 0–255 to a red-green-blue triplet. The tag must contain exactly 768 unsigned numbers in the range 0–255 separated by commas ",". The first 256 values are the red values, the next 256 one the green values and the last 256 ones the blue values. I.e. the format is COLORTABLE=r₀,r₁,…,r₂₅₅,g₀,g₁,…,g₂₅₅,b₀,b₁,…,b₂₅₅.

To embed a value table with numbers inside the image, the tags COLORTABLE and VALUETABLE_FLOAT have to be set. VALUETABLE_FLOAT must contain exactly 256 floating point numbers in text string format separated by commas ",". They map the grayscale values 0–255 to e.g. a physical quantity like temperature. Undefined values can be set by using the value NaN (“not a number”).

To embed a value table with text identifiers inside the image, the tags COLORTABLE and VALUETABLE_STRING have to be set. VALUETABLE_STRING must contain exactly 256 text strings separated by commas ",". They map the grayscale values 0–255 to e.g. categories. The texts can be displayed in the Satellite Layer of the NinJo Client as auxillary information. Undefined values can be set by using the value undef.

External color table

For 8-bit single channel (grayscale) images it is possible to add a colortable via external configuration. The color table maps gray values to RGBA colors. This mechanism is only available for Product type images.

The color table has to be provided as configuration in context ninjo.data.raster.sat.colortable. See section Configuring Colors in the Config Manual for general information on color tables. The color table is used to map values 0–255 (without unit) to RGBA values.

The color table is selected based on the Satellite Name ID and the Satellite Product ID. The configuration name has to follow the pattern SatNameID_SatProductID.xml.

Examples:

File name	Sat Name ID	Sat Name	Product ID	Product Name
7000014_1700015.xml	7000014	NWCSAF Central Europe	1700015	Cloud type
6900014_1800015.xml	6900014	NWCSAF Europe/Atlantic	1800015	Cloud cover

IDs for Satellite Types

IDs for Satellite Names

IDs for Satellite Channels and Products