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GeoTiffExaminer
Disclaimer
This program is provided 'AS IS' without warranty of any kind, either expressed
implied, including, but not limited to, the implied warranties of merchantability and
fitness for a particular purpose. The entire risk as to the quality and performance of the
program is with you. Should the program prove defective, you assume the entire cost of all
necessary servicing, repair, and correction.
What is GeoTiffExaminer?
Raster images in the TIFF format (Tagged Image File Format) can be georeferenced in two
different manners. First, an accompanying file, usually called a World File, may be
provided. A world file carries pixel scale information and the location, in real world
coordinates, of the (typically) northwest pixel.
Second, this same information can be added in specially identified tags in the Tiff
file. In this case, the Tiff file is usually referred to as a GeoTiff. GeoTiffExaminer is
a program which enables users to examine, and modify, the information contained in a
GeoTiff file, or its World File companion.
Examining a Tiff/World File
Start GeoTiffExaminer. You will see a dialog box similar to that shown above. Enter the
full path name of a Tiff file in the box labeled File
Name. A Browse button is provided for point and click selection. Use the mouse, or the tab key,
to move the cursor from the File Name field.
Once the Tiff File Name field loses the input focus, GeoTiffExaminer will open the Tiff file and search
for the magic tags which are used to georeference the Tiff file. If such are found,
GeoTiffExaminer will display the values on the left hand side of the screen.
After examining the Tiff file, GeoTiffExaminer will see if a corresponding world file
exists in the same directory as the Tiff file. If such does exist, GeoTiffExaminer will
open that file and display its contents on the right hand side of the dialog box.
In this manner, you can see if the Tiff file is georeferenced, and if such exists,
examine the information in the corresponding world file.
GeoReferencing a Tiff File
To georeference a Tiff file, open the file as described above. Once opened, you can
manually enter the appropriate values in the field provided in the dialog box and click on
the Update Referencing in Tiff File button. This will cause the georeferencing information to be written to the Tiff
file. Of course, you can use the same techniques to modify existing referencing
information in a Tiff file which is already georeferenced.
Note that the Update Referencing in Tiff File button is grayed out if the selected Tiff file is a read only file.
If the Tiff file has a corresponding World file, you can use the buttons in the center
of the dialog box to copy the World file information to the Geo Tiff area of the screen,
and then use the Update Referencing in Tiff File button to georeference the Tiff file.
Writing a World File
In the case where a Tiff file is properly georeferenced, it is often
desirable to have
a corresponding world file. You can use the Write
new world file button to accomplish this.
Technical Information
GeoTiffExaminer requires that Tiff files have the .tif extension, and that world files
have the .tfw externsion.
GeoTiffExaminer does not support the form of GeoTiff files which support rotation of
the image. It is our guess that most software which can process GeoTiff’s do not
understand that information either. If our guess is wrong, we’ll be updating
GeoTiffExaminer in a future issue of the Casual Cartographer.
Questions/Problems??? Please contact us at:
888-ASK-NORM . 303-279-9366 . 303-278-4099 FAX .
Email:norm@rockware.com
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June/July 1999 |
