Triton TritonMap - Manual (Page 134)

June 2004 DelphMap™ User's Manual
to the computer’s world of row-and-order scheme. Geo-referenced files can do
this if those files make all their geo-referenced information available in a separate
header file. (In fact, if the header file contains geo-referencing, the file is then a
special kind of header file called a world file.)
In the case of DelphMap, the world file has an extension of TFW and is created
whenever a TIFF or GeoTIFF file is exported from DelphMap.
Conveniently enough, this header file is an ASCII file, which can be easily read
and interpreted by a variety of software programs. If the user knows the geo-
referencing that is contained in a given geo-referenced image, the user can even
create the header file apart from the geo-referenced file, without having to run it
through some software that would extract the world geo-information contained in
the image.
A Look at Geo-Referencing in a World File
When your software displays a geo-referenced image on your screen, the
software capable of displaying the image looks for the geo-referencing in any of
these sources, in this order:
1. the world file (if available)
2. the header file (if your image file supports header files)
3. the row-and-column information in the image (also called an identity
transformation)
If more than one geo-referenced source is available, the software uses the
source having the highest priority (1 before 2 before 3 in the above list) and
disregards the other source or sources. An important implication of this rule of
precedence is that if your image doesn’t have a corresponding world file, and you
create one, the created world file takes precedence over the other two sources
because a world file always has highest priority.
Chapter 8: TIFF and GeoTIFF Differences 120