Hello All.

Recently I had to work my way through various issues relating to
using Ozi with GeoTIFF files. I had some problems, some of which
were nothing to do with OziExplorer. Here's a summary of what I
found, in case it helps anyone else.

1)
Anything mentioned here refers to the registered version of
OziExplorer 3.90.3a, and to the current(as of May 5, 2002)
"Tiff File Utilities" available on the "Utilities" webpage
and the "Geotiff Support File" on the "Optional Extras" webpage.

2)
Des is aware that there is a newer version of the GeoTIFF
support library(libgeotiff) available - in an email reply
he said:
"I will of course be adjusting Ozi to make use of the later
libgeotiff library once I see what the changes are."

3)
If you haven't already done so, I'd suggest reading the
following sections in the "Map Related" portion of Ozi's Help File:
"Image Formats Supported" and "Importing DRG Maps".

4)
A GeoTIFF file is a TIFF file containing georeferencing information.
If there is no associated 'metadata file'(e.g. .tfw, .fgd) available,
Ozi can only import a GeoTIFF file if both of these conditions are met:
- you have downloaded and installed the "Geotiff Support File"
- the "Geotiff Support File"(OziGeoTiff.dll) 'understands' the GeoTIFF
information contained in your GeoTIFF file.

5)
Even if you can apparently successfully import a GeoTIFF file, you
should check the map's calibration.
Currently Ozi will import some GeoTIFF files by applying a 2-point
calibration, even though the GeoTIFF file contains calibration information
for more than 2 points. Des has said in an email:
"There is nothing wrong with a 2 point calibration and the big test
is of course if the map is calibrated ok using these 2 points then
there is no problem."

6)
The Ozi help file is not necessarily complete in the section titled
"Importing a Single DRG Map" in the "Importing DRG Maps" section.
Depending on what information is supplied in the GeoTIFF file, if
either Ozi cannot understand some of the required geo-referencing
data, or it is missing from the file, then a dialog box may appear,
as explained in the section titled "Importing DRG's with only a .tfw File".
Sometimes this can be caused by trying to import a GeoTIFF image that
originally came with a metadata file that is no longer available.
Some data providers put only a minimal amount of geo-referencing
information in their GeoTIFF files.

7)
Given Ozi's current GeoTIFF support, I would suggest that the
following be kept in mind as you work with GeoTIFF files:
7-1)
Download and install the "Geotiff Support File", then rename it
to disable it(e.g. rename it to "OziGeoTiff.dll.OFF").
7-2)
If available, make sure you put any metadata files(e.g. fgd, tfw)
in the same location as the images you wish to import.
7-3)
Depending on the information in your GeoTIFF images, and the
format of any metadata file(s), you may find you get a "better"
calibration when not using the "Geotiff Support File".
7-4)
If you find that you cannot import a GeoTIFF image, perhaps
because you don't have a metadata file, you can rename the
"Geotiff Support File"(e.g. rename "OziGeoTiff.dll.OFF" to
"OziGeoTiff.dll") and try again.
7-5)
If you do not have a metadata file for your GeoTIFF image,
you may be able to use utilities to create one. For example,
"listgeo" can be made to create a 'ESRI style .tfw file'.
7-6)
Ozi limits itself to a 3-point calibration for a DRG import,
even if the GeoTIFF file and or metadata file contain more
calibration points. If you feel you need the additional
points, you may be able to use the "listgeo" utility program
to get the additional information from the GeoTIFF file,
and/or by looking at the metadata file with a text editor.
You would then have to add the extra calibration point(s)
to the map manually.
7-7)
Make sure you use up-to-date utilities for working with
GeoTIFF files. The "Tiff File Utilities" currently available
on the Ozi website are out of date.

-----------
Dave Patton
Canadian Coordinator
the Degree Confluence Project
http://www.confluence.org
dpatton@...