Triton TritonMap - Manual (Page 133)

June 2004 DelphMap™ User's Manual
Chapter 8 TIFF and GeoTIFF Differences
A Peek at TIFF and GeoTIFF Differences
Many raster file formats can be displayed as images on a PC. Prominent among
these formats is the TIFF format. A TIFF file can be read by almost all graphical
“paint-style” programs that commonly run on the Windows operating systems.
(TIFF files, usually identified by the file extension TIF, also can be imported into
other, major applications such as Microsoft Word.)
A subset of the TIFF format is the GeoTIFF format. It’s simply a TIFF image that
has extra information about the geographic position of the image. Because a
GeoTIFF is a subset of TIFF, it can be opened as a normal TIFF.
More importantly to the user of the GeoTIFF format, certain programs can
decode the geo-coordinate information inside a GeoTIFF file. A partial list of
companies and products that have this capability are shown in Table 5.
Some companies, such as AutoCAD, have programs that partially support
GeoTIFF. That is, they can import the GeoTIFF format but not decode the geo-
coordinates in the file. Autodesk’s AutoCAD14 is such a program: It can import a
GeoTIFF, but AutoCAD does not directly read the geo-positioning information
contained in the GeoTIFF; to AutoCAD, it’s simply a normal TIFF file. However,
AutoCAD14 does let you assign geographic coordinates to an image. Even so,
AutoCAD14 won't tell you what coordinates to use; you have to get that
information beforehand from some other source, such as DelphMap or a
GeoTIFF viewer.
Note: You can download a free GeoTIFF viewer from the ER Mapper web site
(Table 5). From ER Mapper (or from DelphMap) you can discover the coordinate
information to be accessed.
Mapping Geo-Coordinates to Images
Information in images is stored in row-and-column order, starting from the top left
of an image. However, row-and-column order — convenient though that is for
computers — doesn’t conform neatly to the geographic world made up of x and y
coordinates. Before the row-and-order scheme can be associated with the geo-
coordinate scheme, the geo-coordinate scheme must be mapped, or registered,
Chapter 8: TIFF and GeoTIFF Differences 119