Standard Chartered Hong Kong Marathon 2019 (Chung Lin Cheng)
Lok Wah 100min Half Marathon Elite Race (MaKee Snap Shot)
Sportshouse Hong Kong 10K Challenge 2018 (Cheng Chung Lin)
Chung Hing Cup 2018 (Coey Yuen)
Chung Hing Cup 2018 (wmhy)
12th Launch8 Tolo Harbour 10K Race (Sundae Lam)
12th Launch8 Tolo Harbour 10K Race (Sundae Lam)
Standard Chartered Hong Kong Marathon (HKRun)
Mizuno Hong Kong Half Marathon 2017 (Coey Yuen)
ASICS Hong Kong Island 10K City Race (Cheng Chung Lin)

GPS data through tunnels

Hi all,
What happens to GPS data in the HK marathon tunnels??
Does it extrapolate where you disappeared and emerged? Or does it completely mess up your entire run data?

It'll be my first time doing the HM, and experience running through the Western Harbour Tunnel :)

What I'm worried about is the loss of GPS signal inside there. On a good day, when I run through a short tunnel of about 100m (The Marco Polo HongKong Hotel taxi area), I got teleported 2k away and back in the space of 3secs... needless to say it messed up my Nike+ data, and had to delete the whole 10k run!

What's it going to be like for runners using the Nike+GPS app? Does it somehow still manage to work out where you disappeared and where you emerged from, join the dots, and calculate the tunnel distance?

I'm hoping that it would, and appreciate if anyone can verify that the app or even GPS sportswatches does that.

However, I'm also hedging my bets by trying to calibrate a tiny iPod Nano to trace the run via accelerometer independently of my iPhone. I hope it works!!!!

Re: GPS data through tunnels

When I run through the tunnel on the north side of Discovery Bay with Garmin 305 and when I map it, it shows a straight line and the distance was indicated. Perhaps the tunnel is not as long as the Western Tunnel. Using the nano is a good idea. Also, just before you enter the tunnel, may be you can hit lap and then when you exit tunnel, you hit lap again. Later you can see if any distance was captured. I hope this helps Michael.

Re: GPS data through tunnels

Normally the GPS should trace a straight line from where it looses the signal at the entrance of the tunnel until it gets the signal back at the exit. You can see that on my previous SCM GPS:
http://connect.garmin.com/activity/69119930

I think what happens when you run near the Marco Polo is that because of the dense bulding coverage around you, the GPS has difficulties getting an accurate positioning, but the exit of the Western tunnel and other tunnels on the SCM course are far from the buildings so you should not have that problem.

MichaelCheung's picture

Re: GPS data through tunnels

Thanks Bekrissed and Bakhwee! That's a huge relief for me to know the theory, and that it has worked in practice for you! good luck and hope you get a PB!

Re: GPS data through tunnels

When I ran through the tunnel today, my Garmin lost about 150m. It was measuring 150m ahead of the kilomtere markers just before the tunnel, and 50m behind after. I guess it's because the tunnel is not straight but has a sharp bend at the end.

MichaelCheung's picture

Re: GPS data through tunnels

Yes, you're right, looks like the GPS can only tell where you've emerged from, and then extrapolate a straight line there.

I'm very happy that my Nike+GPS app did perform as the others suggested. http://nikerunning.nike.com/nikeos/p/nikeplus/en_GB/plus/#//runs/gps/478...

Rather more inaccurate in terms of total distance, but not bad given its just a US$2 app!

Re: GPS data through tunnels

for your information. The distance of the measurement line (the actual running line) from entering the WHT (kowloon)to the exit of WHT(HK),龍口位 至 龍口位 is 1.970km