Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performance
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Thread: Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performance

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  1. #1
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    Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performance

    My major moves are long day hikes in the Sierra Nevada. Having done a few with the Ambit2 and Suunto Trackpod, here are the accuracy results.

    Hike 1--Granite Lip: 16 miles RT, 5300 ft. net elevation gain

    Ambit2: Worn on right wrist
    Average EHPE: 9.00 meters
    Warmup time: significant (basically the whole 5 hour trip to the park)

    Trackpod: Mounted on top of stick on my pack, about head height and about 6 inches from my left ear.
    Average EHPE: 4.47 meters
    Warmup time: about 30 minutes an hour before getting to the park, and then only 5 minutes before starting

    So you can see that the Trackpod accuracy was about double that of the Ambit2, even though it had less warmup time. Obviously the favorable mounting position was the reason.


    Hike 2--Kennedy Pass: 24 miles RT, 6400 net elevation gain (trailhead is only about 13 miles from the other one)

    Ambit2: worn on chest strap, about 3 inches to the right of the Motorola Ant+ HR belt coupler
    EHPE: 4.99 meters
    Warmup: An hour or so

    Trackpod: Same mounting position
    EHPE: 3.87 meters
    Warmup: an hour

    Garmin 62sc: worn in pouch on upper left chest
    EHPE: unknown, but prevailing accuracy was 8-10 feet, with as low as 24 feet under heavy tree cover. I would guess average EHPE around 10 feet or so.
    Warmup: 5 hours

    So the Garmin and Trackpod performed with about equal accuracy, even though the Trackpod was in a slightly better position for sat reception. Likely the Garmin has a superior antenna and would perform better under the same mounting positions.

    Even though the Ambit2 accuracy was not as good, it was much improved over wearing it on my wrist.


    HR dropouts on Ambit2:

    Worn on wrist on Granite Hike: zero HR readings turned up in 2.6% of the xlss log

    Worn on chest strap near the HR monitor: When the pack was being worn, only 0.7% dropouts occurred. However during breaks, the watch was left on the pack so I got a lot of zero readings during that time. Not sure if it's worth it to keeping moving the Ambit2 to my wrist during breaks and then putting it on my chest strap, in order to get better data, but considering I'm also getting better GPS accuracy, it's going to stay on the chest strap while moving.

    Better HR monitor syncing is the reason I wore the T6 this way as well, but the problem is worse with the Ambit. Unfortunately, I couldn't use the trusty T6 to measure HR because I wanted to use the Garmin for that, as it will record track/HR/Temp every second. I'm hoping that Suunto will release an Ant+ HR belt in time for next year's hiking season. In the meantime, I'll use the Garmin + Ambit2 for HR on hikes, and the T6 + Ambit2 for runs.

    Anyway, those are the results of my comparisons, FWIW. :)

  2. #2
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    Re: Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performan

    The pod sure is impressive for it's size and weight, 62sc is 8 times bigger.

    What do you think of the actual track accuracy compared to EHPE you get? I am asking because for me the accuracy looks a lot better than what EHPE would indicate if carried on top of hat. So kind of even with similar EHPE readings I feel like getting worse track in upper arm strap than on hat. Been thinking it might combination of the body shadow making the error more consistently to one same direcition (upper arm case) and that making a typical kalman filter less effective, as hat gps errors are more random, better for kalman filter. But that's just guessing and I may be imagining the whole thing.

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    Re: Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performan

    Quote Originally Posted by XCJagge View Post
    The pod sure is impressive for it's size and weight, 62sc is 8 times bigger.

    What do you think of the actual track accuracy compared to EHPE you get? I am asking because for me the accuracy looks a lot better than what EHPE would indicate if carried on top of hat. So kind of even with similar EHPE readings I feel like getting worse track in upper arm strap than on hat. Been thinking it might combination of the body shadow making the error more consistently to one same direcition (upper arm case) and that making a typical kalman filter less effective, as hat gps errors are more random, better for kalman filter. But that's just guessing and I may be imagining the whole thing.
    I haven't compared that yet, but it would be hard to do so on a trail unless you can actually see the trail on Google Earth. I'll see what I can find out when I get some time. One thing to check for is how close together the up/down tracks are. The closer together they tend to be, the more accurate (especially if they appear to coincide). Of course, body shadowing could cause the tracks to be further apart then they otherwise would be, but I don't mind that error so much as long as the error is consistent and so I get the correct distance and ascent/descent data (although on a steep slope it could affect the altitude readings somewhat, since GPS is used for calibration).

    Probably the best place to check for that would be on a street or on an oval track though. Would be an interesting experiment.

    Regarding the stated EHPE, my guess is the actual accuracy on average would be about half of what it's estimating. That is, when it estimates 3 meters, then it means the actual position is within 3 meters, not that it actually is 3 meters. So the actual error is between 0-3 meters, and probably somewhere in the middle. Anyway, EHPE is really just a measure of signal strength, which is the important thing. The better the signal, the better the track (as a general rule). The Ambit2 track suffers because it doesn't record every second but rather every 15 seconds or so (on hikes), so you get a lot of switchback cropping.
    Last edited by bruceames; August 27th, 2013 at 15:37.

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    Re: Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performan

    One thing that can be very useful is for Suunto to bring out the EHPE as a parameter that can be monitored on the watch. On my fenix or the other Garmin handheld devices, I don't start my exercise right after the device locks on the satellites but I keep waiting until the "accuracy" parameter reduces and flattens out (an extra 2-3 min.)

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    Re: Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performan

    Quote Originally Posted by idgsd View Post
    One thing that can be very useful is for Suunto to bring out the EHPE as a parameter that can be monitored on the watch. On my fenix or the other Garmin handheld devices, I don't start my exercise right after the device locks on the satellites but I keep waiting until the "accuracy" parameter reduces and flattens out (an extra 2-3 min.)
    Yes I agree it would be very useful. Also if it would give the average EPHE at the end of a move it would be a killer feature, IMO. To know how well a track recorded, or is recording, is something I think just about everybody would be interested in knowing.

    However, at least Suunto has the data available in the xml file, for post analysis, should anybody want to take the trouble. It takes me about 10 minutes or so of a long move (almost a million rows in Excel!) to get the EPHE values I'm looking for. Garmin doesn't provide accuracy data in their files (at least those files I have seen).

    It's possible that Suunto thinks that it's in their best interest that people don't have the mindset to wait around until the EHPE drops to a certain level and that the watch is ready to go after it beeps in two seconds. The Ambit2 especially is famous for superfast GPS syncs and throwing accuracy into the mix may not go well with that selling point. Who knows though for sure.
    Last edited by bruceames; August 28th, 2013 at 01:24.

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    Re: Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performan

    After looking at the tracks on Google Earth, it looks like the Garmin track is the best, followed by the Ambit2. The Trackpod has the poorest track. Here is a sample of each...


    Garmin 62sc
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    Ambit2
    Name:  Ambit2.jpg
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    Trackpod
    Name:  Trackpod.jpg
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Size:  257.8 KB

  8. #7
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    Re: Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performan

    Another sample...

    Garmin 62sc
    Name:  Garmin62sc2.jpg
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    Ambit2
    Name:  Ambit22.jpg
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    Trackpod
    Name:  Trackpod2.jpg
Views: 487
Size:  286.0 KB
    Last edited by bruceames; August 28th, 2013 at 04:29.

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    Re: Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performan

    Quote Originally Posted by bruceames View Post
    Trackpod
    Name:  Trackpod2.jpg
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    Hmm, there is systematic error left or right. I don't get similar error if I place my pod properly. But I do get that too if I place it "wrong", let it shoot left or right. You had it on top of stick, right? Was the antenna shooting straight up (flat part with button straight up), like it would on top of hat, or was it shooting sideways? I believe you had it shooting left or right, making vulnerable to reflections from that direction resulting systematic shift. If you remember where it was shooting, you can confirm it by taking a look at the track shift actually is to the very same direction antenna was shooting.

    Take a look at typical patch antenna pattern here: Patch antenna - Wikipedia, the free encyclopedia
    and imagine shooting sideways. You end up having quite bad signal strenght for the half of the sky and satellites at thet part are not be seen directly, but instad reflections are used.
    Name:  26b.jpg
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    For the ambit and 62sc you may have had the antenna aimed more right, or at least 62sc's antenna must have been shooting straight up if carried in breast pocket. So, if it was not alerady shooting straiaght up, I'd say before claiming pod's track is poor try aimimg it up once (and perpare to get amazed ;).

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    Re: Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performan

    Name:  Trackpodpic.jpg
Views: 454
Size:  196.7 KB

    I do indeed have it pointed straight up, although from the pic it may at about 5 degree angle. But a pack or even a head is always going to be weaving or bobbing so you have to expect that.

    In any case, it reads much better up there than it did on the arm strap.

    I would like a better track but I surely can't expect it to compare to the Garmin 62, which has a much better antenna. You can see the pouch for the Garmin near my left shoulder. It is nowhere near pointing straight up, but at least it is getting a good view of the sky.

    Keep in mind that these tracks were taken on very steep slope in a deep canyon (Kings Canyon National Park), so the conditions weren't ideal for satellites for any of the devices.
    Last edited by bruceames; August 28th, 2013 at 15:33.

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    Re: Comparison of Ambit2 GPS with Trackpod and Garmin 62sc and Ambit2 chest-mounted HR/GPS performan

    Quote Originally Posted by XCJagge View Post
    So, if it was not alerady shooting straiaght up, I'd say before claiming pod's track is poor try aimimg it up once (and perpare to get amazed ;).
    It certainly had the best view of the sky of the three devices, and yet had the poorest track. If you see anything that can be improved upon, let me know. :)
    Last edited by bruceames; August 28th, 2013 at 15:51.

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