Electronic – GPS Data Accuracy on Inclines

gps

I have a BU-353, and I am using it in a car. I want to use it to get a more accurate speed reading than RPM/wheel diameter calculation can give me. I am wondering how the incline of a slope, that the car might be going up would impact the GPS reading (specifically NMEA VTG and RMC data). In other words, would the speed out put from the GPS be inaccurate if the altitude of the car is changing, and if so how could I account for that in the software?

The device can also use the following NEMA Protocols: GGA, GKK, GSA, GSV, RMC, VTG, MSS, ZDA

Best Answer

Next to longitude and latitude data GPS gives also altitude information. It's up to the receiver's software designer to decide if she uses that information. She should, and then the speed is determined by

\$ Speed = \dfrac{\sqrt{(\delta \mbox{ } longitude)^2 + (\delta \mbox{ } latitude)^2 + (\delta \mbox{ } altitude)^2}}{\delta \mbox{ } time} \$

Note that distance as a difference in latitude is constant (111.1 km per degree), while for longitude it's function of latitude: 111.1 km per degree at the equator, 71.4 km per degree at 50 degrees north or south, for instance.

edit
The BU-353 supports NMEA's GGA sentence, which gives you essential fix information including longitude, latitude and altitude.

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