Use GPS longitude/latitude to calculate speed

lewkahkang

I am currently assessing the validity and reliability of a GPS (VXSport) device. I am trying to work with the raw data export which only provides speed and longitude/latitude (less altitude) data. VXSport has mentioned that the speed data that they obtained in independent of the longitude/latitude coordinates, mentioning that it is recorded directly from the GPS chip.

One of my tasks is to calculate speed using the longitude/latitude coordinates so that I can compare this value to that of the speed value recorded directly from the GPS chip. What I have done is that I have referred to this research paper specifically obtaining the section on user velocity http://d1.amobbs.com/bbs_upload782111/files_33/ourdev_584835O21W59.pdf but it seems that there is a lot more information required that I am unsure how I can obtain them, for example, XYZ coordinates of each satellite connected, frequency correction determined from navigation message updates.

Aside from branching to other topics such as Kalman filtering, I also understand that these iterative calculations may be done via computing programs instead of solving it in a mathematical. I would like to hear anyone's honest opinion regarding my project and especially if anyone could recommend me to any resources as to how GPS calculate speed using the longitude/latitude coordinates ideally with numerical examples.

I deeply appreciate anyone who has taken time to go through my thread and sincerely apologize if I had stated any information incorrectly. Please feel free to let me know if there are any issues.

Thank You!

Boyd

Sounds like a good project and I hope you get some responses. But I think you have come to the wrong place. For starters, there is very little activity on this site anymore. Beyond that, when someone does come here it is generally to ask a question like "how do I update the map on my Garmin GPS?" This has always been a consumer-focussed site, and not a place to discuss complex technical topics. :)

And before you ask... no, I have no idea where you would find a site to discuss this kind of thing, sorry.

Tim

Hi @lewkahkang,

That question is above my pay grade as well, although one thing stuck out to me in your post.

VXSport has mentioned that the speed data that they obtained in independent of the longitude/latitude coordinates, mentioning that it is recorded directly from the GPS chip.

While a GPS chip may provide speed data, I suspect they are only calculating it based on the time and position data the chip calculates. Afterall, the only thing a GPS chip does is fetch the current time from the satellites, nearly everything else is calculated on-chip.

So any speed calculation you do might not be any better than the speed calculation the chip is performing.

lewkahkang

Tim said:

Hi @lewkahkang,

That question is above my pay grade as well, although one thing stuck out to me in your post.

VXSport has mentioned that the speed data that they obtained in independent of the longitude/latitude coordinates, mentioning that it is recorded directly from the GPS chip.

While a GPS chip may provide speed data, I suspect they are only calculating it based on the time and position data the chip calculates. Afterall, the only thing a GPS chip does is fetch the current time from the satellites, nearly everything else is calculated on-chip.

So any speed calculation you do might not be any better than the speed calculation the chip is performing.

Hi Tim really appreciate your response, if you might just think of any resources that might provide me insights with satellite information please do let me know thank you!