MB Gravity Elevation Correction

Bringing GPS Elevation Down to Earth™

MB Gravity™ is our next solution to just one of the many accuracy issues that are present when using GPS to train and record your outdoor experiences.

The Problem

Too many activities have displayed that 100 meter spike when viewing an elevation profile in the Dashboard.  This often occurs when the satellite signals are blocked from the sky above (trees, buildings, deep canyons).  Even though your horizontal location is still accurate enough to place you on the correct side of the road, the third dimension (alititude) is harder for your GPS unit to calculate...it requires a lock on four satellites where location only requires three.

Even if you don't get a big spike, it is often a bunch of little spikes that end up causing incorrect cumulative statistics.  We call that the Elevation Heart Attack. 

Nuts and Bolts

MB Gravity is a MotionBased.net web service that will cross-reference the horizontal location of every point along a GPS track and provide a more accurate and consistent elevation value provided by an elevation database built by the government.

Results

So what does all this mean for you...better elevation statistics.  Total Elevation Gain/Loss, no more spikes, more consistent grades.  Distance calculation will be more accurate because we won't be measuring the extra distance required to travel up and down all that incorrect elevation.  The MB Tune Up™ auto corrections won't need to be so agressive because the numbers will make more sense.

Let's take a typical ride with our good friend Randy Warren (you know him as rwarren on the TrailNetwork).  Randy lives in the Great Plains as many of you do.  No offense, I grew up in Minnesota myself.  Randy's ego has been stroked by MotionBased because his GPS reports him as being a stud climber.  Well, his numbers have been wrong sorry to say.  View this before and after situation:

Before MB Gravity

Few things to notice...Is this an elevation heart attack?  Did Randy really do 2,700 feet (820 meters) of climbing?  I think not! Was he picked up by a bird flown up a few hundred feet and dropped back down?  I really think not!  Why does this ever get reported to MotionBased by the GPS unit??? We have no idea, but we don't like it any more than you do!!!

After MB Gravity

So check this out?  The map looks like the same activity, but the elevation profile would make you think otherwise.  2700 feet is now 533 feet.  The elevation that was reported by the GPS unit was off by about 5x off reality.

This is just one example of how MB Gravity is going to help your numbers make some real sense.

Current Limitations

O.K.  MB Gravity is way cool.  I am not selling you snake oil just to get a subscription or two, but there are some known limitations to MB Gravity.

1. It works much better on roads and flat terrain than it does on steep grades or trails on a steep hillside.  We have a plan to fix that.
2. If you are crossing a bridge, MB Gravity will think you are swimming.  Don't worry we have a long-term solution to this problem...it's you!  Be sure to track all of your rides at MB so we can use the data collected from all the other activities on the TrailNetwork to know that you were high above the water.
   
   
   Notice the big square drop on the MB Gravity corrected photo on the right compared to the original on the left.  This is crossing the Golden Gate Bridge.  Too bad since you can see the profile at the end of the corrected photo looks a lot better than the original on the left.
   
   
3. You have to choose to apply the corrections to each activity.  It is not automatic.  We will eventually be providing you a way to easily correct all of your activities at once so don't spend too much time correcting the historical.  We wanted to get some more feedback before we go correcting our 50,000 activities and slowing down an already overburdened server.

Who will benefit?

I do imagine we could get a few more of you to pay for a yearly subscription if we charged for MB Gravity.  It will put an exclamation mark at the end of the bullets that differentiate MotionBased from other GPS mapping and training solutions.  MB Gravity is avaialable to all MB Customers both Lite and Standard. 

Here at MB we don't feel that anyone should have bad data.  Providing MB Gravity to everyone will benefit the community by putting more trust into their GPS training experience when coupled with MB.  We have plenty of features left to implement and yes they will only be available to Standard customers, but our MB Tune Up and MotionBased Everywhere™ products will be available to all.  You may not understand why just yet, but trust us on this one...it will pay off.

How and When?

MB Gravity is available right now at MotionBased.com since Monday, May 9th. 

Just view the activity of interest, click on Activity Options in the upper right corner when viewing the Dashboard or Map Player and choose MB Gravity Checkbox.  Notice that auto-corrections is required to be enabled at this time.

Remember, we will be providing a way to correct all your existing activities at once so don't get carple tunnel checking that MB Gravity box.  We want you to spend your time outdoors and not on the computer doing maintenance...that's our job!

Last note...Thanx to Brad Culberson a fellow MB Tester for implementing the MB Gravity Web Service on contact with MB. Brad, your efforts are much appreciated and you've done the GPS Fitness community a great favor by helping us get MB Gravity built quickly and with great quality.

Aaron
The Digital Trailblazer™

Comments

[damo]

This sounds great!

Cheers,

Damo.

[Jeff King]

When will this be available to Canadians???!

[Clark]

No date set for MB Gravity outside of the US.

We are looking for a usable format of elevation data for other countries. We are also looking for volunteers to help implement MB Gravity for other countries.

If you're a software engineer familiar with web services and keen on getting MB Gravity in your country, please send an email to support@motionbased.com

[Koop]

Very cool

[Andrea]

I used the MB gravity correction for a ride that I did this weekend on the peninsula--old la honda, pescadero, tunitas creek. This is a really hilly ride and the uncorrected readout gives 7500 ft of elevation gain in 65 miles, but the Gravity correction gives over 8500 ft of climbing, which is obviously way off.

Should I not use the Gravity correction for hilly rides?

[Clak]

We have found that MB Gravity works best on flat to hilly terrain. As soon as you get into the mountains with significant drop-offs from the road, we've found that MB Gravity is picking up too much of the hillside, thus increasing the elevation totals.

Obviously, we need to fix this but it will take some time. For the now, if your activity is primarily flat or slightly hilly, use MB Gravity. Otherwise, stick with the GPS elevation.

[Kevin]

Interesting concept -- I'm new to GIS and was wondering how this concept could apply to making elevation corrections to calculated latitude / longitude distance?

I have a website where runner's can plot their routes and I've just recently launched an elevation profile lookup. I'd like to be able to offer elevation distance correction. Is this possible?

-kevin
mapmyrun.com

[Ron]

I just did a ride in the same area that Andrea posted. I know there have been issues posted regarding elevation gain, but are there issues with the elevation reported? I guess if I take the peak elevation data, and extrapolate the data, I might get more accurate elevation gain? Others on the ride reported total elevation gain as 6900 ft, while after posting the data from my Edge 205, I get 11,124 ft (even after the MB Gravity correction).

[James]

I've noticed that using my edge 305, which has an altimeter, often results in a different number of feet climbed and descended even though I start and end at the same point. How does MB gravity deal with a gps device that is computing elevation from an internal altimeter rather than from the gps signal? I would love to find a way to correct the error.

[Clark Weber]

James,

MB Gravity works the same regardless of whether the GPS device is using a barometric altimeter. We usually recommend NOT using MB Gravity if you have a barometric altimeter because that should give you the purest elevation data. The gain/loss numbers are rarely the same even with an altimeter, but they should be relatively close. What is the discrepency?

[Rick]

I have just started using a Forerunner 205. I run on a fairly hilly (not steep) trail system. It appears to me that the reported distances, both from the device and from the MotionBased reports, are shorter than I have actually run. I had guessed that it was because the elevation changes were not taken into account in the distance covered, but from the comments on the website it appears that should not be the case. Have I just been deluding myself in the past about how far I was going, or is there something else going on with the system?