MITIFF

Author

Øystein Godøy, METNO/FOU, 16.02.2006

W5 of MITIFF

What?

MITIFF is an implementation of geocoded information in TIFF 6.0. The difference bewteen a standard TIFF 6.0 image and the MITIFF image is the special formatting of the TIFF commentary tag. This is formatted with information required for geolocation of the image. The reason this formatting is used and not the GEOTIFF standard is that the GEOTIFF standard was not available when the MITIFF was needed. More info on the ASCII tag wil be given below.

Why?

GeoTIFF was an idea, but not a functional library when MITIFF was created. If GeoTIFF had been available, this would have been used instead.

Where?

MITIFF was developed for visualisation of meteorological raster data (e.g. satellite and weather radar data) in a meteorological work station. MITIFF is implemented in various local libraries at the Norwegian Meteorological Institute. The reference implementation is the libsatimg implementation. This is the basis for the use in DIANA. libsatimg is now being phased out and support is added to libfmio instead. Libraries are available upon request.

When?

MITIFF was defined in 1994 with only minor adjustments since tehn.

Who?

The original version was defined and implemented by Øystein Godøy, adjustments have been performed together with Steinar Eastwood.

Fundamentals

TIFF 6.0

TBW

User Coordinate System

The User Coordinate System (UCS) system is the navigation system used within the USGS mapping software PROJ.4. Basically it is a Cartesian coordinate system having origo at the North Pole. Positive x-direction is eastwards and y-direction southwards in the Pacific. The following variables are used to navigate images in this system:

Ax - size of the pixel in km in x-direction (must be the same as Ay)
Ay - size of the pixel in km in y-direction (must be the same as Ax)
Bx - distance in km from 0°E to upper left pixel of the image
By - distance in km from the North Pole to upper left pixel of the image
iw - image width in pixels
ih - image height in pixels

All distances are given for the center point of the pixels. Images are always presented in Polar Stereographic map projection correct at 60°N aligned along the 0°E (Greenwich) meridian. A graphical outline of the configuration is given below.
UCS outline

Geolocation information

An example of the MITIFF geolocation information and an explanation of the elements is given below. When presented here newline characters are also visualized.

Satellite: NOAA-16     \n 
Date and Time: 09:38 26/10-2001 \n 
SatDir: 0\n 
Channels: 5 In this file: 1 2 3 4 5           \n 
Xsize: 1000 Ysize: 1000\n 
Map projection: stere                         \n 
TrueLat: 60.00 N GridRot: 0.000\n 
Xunit: 1000 m Yunit: 1000 m\n 
NPX: 0.000000 NPY: 0.000000\n 
Ax: 1.500000 Ay: 1.500000 Bx: -266.731445 By: -2301.237549\n 
Calibration VIS: A=(0.000000)+(0.392157)*C\n 
Calibration IR: T=(323.000000)+(-0.500000)*C

The geolocation information is a specially formatted text string located within the TIFF tag for "Image description". It is composed of a sequence of keywords and data content. The keywords are not only a single word, but can also be a sentence. The keywords can be grouped in sections, not being physical sections clearly identified in the header, but sections by purpose.

The first section describes the satellite data and contains the keywords:

Satellite: - name of satellite or data source
Date and Time: - hour:minute day/month-year
SatDir: - Rarely used...
Channels: - Number of channels in the file (e.g. 5 AVHRR channels)
In this file: - Identification of the channels by number or text string

The second section describes the image:

Xsize: - Number of pixels horisontally (also found elsewhere in the tags).
Ysize: - Similar as Xsize but for vertical size.
Map projection: - Only Polarstereographic is used at METNO (stere is the definition of polarstereographic in the PROJ software).
TrueLat: - Latitude for the Polarstereographic projection. Always 60 deg N at METNO.
GridRot: - Rotation of the projection around the 0 deg longitude. Always 0 at METNO.

The third section describes the Universal Coordinate System used both in the MITIFF and MEOS/HDF files:

Xunit: - Unit used for Ax and Bx. Always 1000 m, meaning 1000 meters at METNO.
Yunit: - Unit used for Ay and By. Always 1000 m, meaning 1000 meters at METNO.
NPX: - Position of the North Pole in the coordinate system x-direction. Always 0 at METNO meaning the Universal Coordinate System (UCS) data used refer to a righthanded coordinate system with origo at the North Pole.
NPY: - Position of the North Pole in the coordinate system y-direction. Always 0 at METNO meaning the Universal Coordinate System (UCS) data used refer to a righthanded coordinate system with origo at the North Pole.
Ax: - Referring to the Xunit this is the pixel size in x-direction (east/west referring to a righthanded coordinate system) in kilometers.
Ay: - Referring to the Yunit this is the pixel size in y-direction (north/south referring to a righthanded coordinate system) in kilometers.
Bx: - Referring to the Xunit this is the distance in kilometers of the upper left corner pixel in the data matrix from the Greenwich meridian. Positive x-direction is towards the East.
By: - Referring to the Yunit this is the distance in kilometers of the upper left corner pixel in the data matrix from the North Pole. Positive y-direction is towards the Bering Strait thus it usually a negative number at METNO.

The final section defines calibration information or palette image information and is not further described here.

Library reference

int MITIFF_read(char *infile, unsigned char *image[], struct mihead *ginfo); - read standard greyscale TIFF 6.0 files containing specially formatted ASCII commentary tag.
int MITIFF_read_imagepal(char *infile, unsigned char *image[], struct mihead *ginfo, struct miheadpal *palinfo); - read palette color TIFF 6.0 files containing specially formatted ASCII commentary tag.
int MITIFF_write(char *outfile, unsigned char *image, char newhead[], struct mihead ginfo); - write standard greyscale TIFF 6.0 files containing specially formatted ASCII commentary tag.
int MITIFF_write_multi(char *outfile, unsigned char *image[], char newhead[], struct mihead ginfo); - Do not use at present.
int MITIFF_write_rgb(char *outfile, unsigned char *image[], char newhead[], struct mihead ginfo); - write RGB composite TIFF 6.0 files containing specially formatted ASCII commentary tag. This is used for presentation purposes e.g. combining AVHRR channels 1, 2 and 4 and the applying the software [satsplit] to the resulting files. [satsplit] puts landcopntours etc on the image.
int MITIFF_write_imagepal(char *outfile, unsigned char *class, char newhead[], struct mihead ginfo, unsigned short cmap[3][256]); - write palette color TIFF 6.0 files containing specially formatted ASCII commentary tag.
void MITIFF_head(char imginfo[TIFFHEAD], char satellite[16], char time[17], short satdir, short zsize, char chdesc[20], int xsize, int ysize, char projection[30], char truelat[10], float rot, int xunit, int yunit, float npx, float npy, float ax, float ay, float bx, float by, char *calib); - create the ASCII string to put in the TIFF commentary tag containing geolocation info and more. see below for details.
int fillhead(char *asciifield, char *tag, struct mihead *ginfo); - internal function used by read functions
int fillhead_imagepal(char *asciifield, char *tag, struct miheadpal *palinfo); - internal function used by read functions