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GeoTIFF

Introduction

GeoTIFF is a TIFF image with extra tags that say where on the Earth it lies: which coordinate system it uses and how its pixels map to coordinates. It is the standard format for raster map data, such as satellite and aerial images and elevation models, where each pixel may be a height or a measurement rather than a colour. It was developed in the 1990s and became an Open Geospatial Consortium standard, GeoTIFF 1.1, in 2019.

Because the extra tags are ordinary TIFF tags, any TIFF reader can show the image, ignoring the location. A Cloud Optimised GeoTIFF (COG) is a GeoTIFF arranged in tiles, with smaller overview images, so that a program can fetch just the part it needs over the web.

Structure

A GeoTIFF is a TIFF file, starting with II or MM, or a BigTIFF for files over 4 GB. The location is given by these tags:

TagNameHolds
33550ModelPixelScalethe size of a pixel in map units
33922ModelTiepointpixel positions tied to map coordinates
34264ModelTransformationa full matrix from pixels to the map, used instead of the two above
34735GeoKeyDirectorythe GeoKeys: the coordinate system, units, datum and projection
34736, 34737GeoDoubleParams, GeoAsciiParamsnumber and text values used by the GeoKeys

Most files name their coordinate system with an EPSG code stored in a GeoKey. Image data is stored in strips or tiles, often compressed with DEFLATE, LZW or JPEG, as in any TIFF.

Also used for

Links

Software

Developers

Reference