... I also built a GPS data stream reader using an Atmel Micro Controller... you can buy the chips for a few dollars each, then hit the ground running with a lot of really nice (and free) development software. As you probably know, there's lots to do and never enough time for all of it.
I have some used cell-site pull, Trimble Thunderbolt GPSDO units in service. I can connect a PC to the serial output port and monitor the status of any one unit, but that ties the PC/laptop to the unit for the duration of any monitoring requirement. It has become popular for people to make up micro controller boards and "fit around boxes" that monitor and display the GPS/GPSDO "TSIP" serial stream on a small (most often) 2-line LCD. The constantly rs-232 serial port monitoring LCD display can and does provide a lot of information including altitude. I mostly need to know if the GPSDO is locked and reliable as a stable 10 MHz reference. Hams and a number of other experimenter types calling themselves "Time Nuts", have really picked up the entire GPS, Time and Frequency measurement "hobby"... actually a very serious hobby for some. So there's lot of stuff around about reading the Trimble "TSIP" Stream and various boards and projects that do that sort of thing. A lot of already completed stream readers and complete readers with mounted GPS units are all over Ebay. And the prices are falling down for the various models and options. I populated a board, used the Mega 8515-P and a simple LCD to monitor the GPS Stream. A friend and I used Studio 6 or Studio 7 with some pre-existing C code information and developed our versions, also in C. New Zeland Ham Radio Friend Chris offered boards on Ebay, don't know if he still does... but they work and all the information is there including the software. https://sites.google.com/site/zl1cvd/tsip I've also used the cheaper Nortel GPS, but it's a bit of a power hog and quite a bit larger. Trimble Thunderbolts are now getting hard to find working and cheap... but any decent GPS and/or GPSDO will do the trick. I built my units for under $15 to $25 max spent each, US dollars by ordering all the parts. If you already have the micro controller you want to use, then you're well on your way. One of the attached pictures is of an Ebay offered TSIP board that fits over the front of a Trimble Thunderbolt. I'm not any kind of fan of that system, but others like it. For some strange reason, I don't have a picture of the front of one of my constructed units, but I will attach some side and back side pictures to show how much smaller it is. Only the side view shows the attached 2 line LCD display. The other pics are main board front and back. I have all the information for a lot of different stream readers and reference material for where everything came from if you get motivated and want to dive in.