Considerations
If you plan to use GPStoFS along with your GPS receiver as a sole source navigational / flight instrumentation system and intend to shoot ILS approaches in hard IMC or fly at night in the mountains threading your way through the valleys, then I have a few suggestions.
General Overview
GPStoFS provides an interface between a GPS receiver and Flight Simulator 2000 from Microsoft. You connect your GPS receiver to your computer (usually a laptop) through a serial cable. GPStoFS takes the position, speed and altitude data from your GPS receiver and 'forces' Flight Simulator 2000 to fly with the same parameters.
Getting started
You will probably be testing this program for the first time on the ground. If your GPS has a 'simulator' mode then you will probably want to use it, otherwise you won't move.
FS2000 must be running, so start it first. Select GPS-Airplane from "Select Aircraft" on FS2000. I have found it useful to have a saved flight available that has everything already set up and the plane at a nice cruise speed (120kts) and a safe altitude (3000ft or so). The position can be anywhere but I usually have it set close to where I am flying from. You might fly the FS GPS plane a bit just for fun. It is a very light weight plane with lots of horsepower but also lots of drag. This is so it responds rapidly to commands sent from the GPS unit.
The first time you run the program it will ask you to set the communication parameters for the com port. Of course you have plugged your GPS to the com port and now you will enter the pertinent numbers. Unless otherwise specified the NMEA-0183 standard expects data sent at 4800 baud with 8 bits, no parity and one stop bit. My GPS (Lowrance Airmap300) allows me to change those parameters to a faster baud rate and with selectable parameters. You might check your GPS instructions and see what is available. I set mine to 19200 baud and left everything else the same. NMEA-0183 data is sent in 'sentences'. GPStoFS only cares about two types of sentences: GGA and RMC. It ignores other stuff. If your GPS receiver allows, you can turn off the other stuff. Make sure you check that it is outputting GGA and RMC sentences though.
Hopefully GPStoFS is running now. To start controlling FS click on the 'Start' button. If your communications parameters are correct you should start seeing the GPS Squawk light blinking every few seconds. That means it is receiving data from your GPS. My Lowrance Airmap300 sends data every two seconds or so. I'm not sure about the other receivers out there.
Looking back at FS2000, the plane should now be flying at the same TAS as the GPS GS and at the same location. There are two modes of flying: normal and slew. Normal flying occurs by default whenever you are more then 100agl and more then 40kts. If you are on the ground taxing or stationary then the GPStoFS automatically switches to 'slew' mode. Slew mode makes FS2000 a moving map display only. It updates your position and heading but the plane is not 'flying'. Once you have met the >100agl and more then 40kts criteria, GPStoFS tells FS2000 to 'fly'. In slew mode the FS2000 movement is jerky and sudden since it jumps to the location each time the GPS sends it's location. In normal mode FS2000 is flying and motion should be smooth with an active airspeed indicator and instruments.
QC and Position
For QC and fine tuning you can select Position QC from View on the menu bar. The blue circles represent the last 5 positions from your GPS. The red circles are the corresponding FS positions. There is usually a difference. There seems to be a variety of reasons for this difference and later versions of this program should correct for them, but for now there are some things you can do. There are three Fudge Factors that you can manipulate to get a better and more consistent agreement between FS and your GPS position.
Calibration and Wind
You can 'calibrate' GPStoFS so that it agrees with the real airplane's speed, headings and altitude. The main reason there is a difference is because of the wind. Once you have made sure you have the correct OAT (Outside Air Temperature) and Altimeter setting then put in the observed MH and IAS from the plane's compass (DG or magnetic) and airspeed indicator. Also, check that the GPStoFS altitiude is the same as the plane's. It comes from the GPS and may be slightly inaccurate. Clicking Calibrate will automatically calculate the wind and TAS. Clicking Calibrate on the Altitude calculates an difference between observed altitude and GPS altititude. Future GPS altitudes are 'corrected' by this difference. At the time of this writing I have not tested this in an actual airplane so I'm not really sure how accurate it is to add a simple correction to the GPS altitude. With SA (selective Availability) turned off the GPS altitudes might be better. Altitude, Altimeter Setting, Temperature and Wind are also sent to FS so that the virtual plane thinks it is the same.. TAS (True Airspeed), DA (Density Altitude) is also computed based on altitude, temperature and altimeter setting.
You can see a pictorial representation of the effect of wind on your plane by selecting Wind Compass from View on the menu bar. The wind direction is relative to the plane (not actual) and the headwind and crosswind components are displayed.
Finally
This is the first release of this program. I intend to make a more intricate version in the future which includes better updates, position interpolation, and outside instrumentation. Good luck and don't take it too seriously....