Answer may be long but it is really simple to do
Waypoints and all other GPS data is stored in the unit's internal memory and is not erased when the unit is powered off. It can be exported to an SD card but the unit does not do this automatically (the menu to do this is called "Export All Nav Data" which is under the "Nav" menus in the Main Tabbed Menu System).
Once the GPS data has been exported to the SD card, the file can than be saved directly to your PC by use of an SD reader/writer (available at most electronics retailers). However, this will be in our current *.hwr file format and not usable by anything else besides a Humminbird unit or our HumminbirdPC program. If you were to transfer this GPS data file to the HumminbirdPC program (using the "From MMC/SD" function), you could than either export it as a *.txt or *.gpx file or save it as a *.gpx file which are usable by other programs.
GPS data from other manufacturers (Garmin and Lowrance) as well as those that use the *.gpx format can be imported into the HumminbirdPC program and than either transferred to an SD memory card (using the "To MMC/SD" function) or saved as a *.gpx file for later use.
At any time that the GPS data is in the HumminbirdPC program, the waypoints may be modified, added to or deleted and Routes may be set up and/or modified.
Once you use the HumminbirdPC program to transfer the GPS data to the SD memory card (not "saved" by using the "Save" function: you have to use the "To MMC/SD" function for this), you can insert the SD memory card into your unit and it will automatically add the new GPS data to what is already in the unit when it is powered on.
Not only a rocket scientist but I have stayed at a Holiday Inn...
I'm guessing that the reason that all the manufacturers have their own formats is all due to patent laws or the possibility of being taken to court over it. Besides, if we all used the same format than everyone would be able to easily change brands! LOL! I'm betting that it will take an aftermarket company/individual to develop a format or program that would allow all of the major manufacturers units to be able to easily interchange GPS data. The *.GPX format may be it. There are many GPS management programs that use it and all can be converted to and from it but I don't think that any actually use this format within their units. To do so I'm betting that there would be quite a bit of software re-writing which would cost a company much needed money and personel resources.
Ken, if you need further explanation of anything I've posted just contact me via e-mail and we will work it all out. gwalters at johnsonoutdoors.com
I've designed a couple of (model) rockets which mostly flew in the right direction (up) but no one actually got hurt. I was a member of the "Mad Scientist Club" while in the 5th grade (looking at some of the strange/dangerous/plain nutty things I have done; I should still be a card carrying member!). I have also (nearly) sunk boats on three different occasions. So it looks like I'm in the right place! :D