Comment 7 for bug 1096477

Unfortunately in version Viking 1.3.* (and I think all the 1.* versions) if you load a GPX file or a KML file and then perform File->Save or use the toolbar Save button - Viking will save the current data in it's own internal format - overwriting whatever file the data was loaded from.

The work around is to avoid using 'Save' and use either the 'Save As' or use the TrackWayoint Export option to save as a GPX or KML.

Some fixes and improvements in this area have been made in the current master code baseline, to ensure that files are not overwritten this way without user confirmation (and the fact they would be of a different type).

In particular these commits (but there are more)
http://viking.git.sourceforge.net/git/gitweb.cgi?p=viking/viking;a=commit;h=c38eb4511f6439744c5967c35bd328921fdea3bd
http://viking.git.sourceforge.net/git/gitweb.cgi?p=viking/viking;a=commit;h=0a51445196a2f5c8869eda3b9e745538c1a76777

This will be included in the next Viking 1.4 release.
I hope the Viking 1.4 release will be made in time to make it into Ubuntu 13.04

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Many file types are not 'directly' supported via the file->open method. (Including the '.ovl' type).

These files have to be imported via GPSBabel and you must tell it what type of file it is (the file name extension is irrelevant in the import process).

Go to File->Acquire->Import file with GPSBabel.
In the new dialog select the file to open and then select the file type (for '.ovl' select "Geogrid-Viewer ascii overlay file").
Then select OK.