> GPS was designed to navigate ships at sea, when they are out of range of all land-based radio beacons.

You're thinking of Decca Navigator. GPS was designed to guide US military targetting solutions. But you're right in saying it's moved on from that.

 

My handheld GPS unit records data points every second. I'm guessing this is the rate for most. Also, it reports a velocity accuracy of 0.1 mph. You are really going to have to be traveling very fast and in a very tight circle before a significant error is introduced. As for the left lane/right lane issue, again you will have to be driving in a tight circle to make that effect significant.

 

It may be more helpful to look at some actual GPS data:

$GPGGA,090329.359,3436.7736,N,08634.0463,W,1,04,1. 8,144.4,M,-30.3,M,19.0,0000*7C
$GPGGA,090330.359,3436.7734,N,08634.0462,W,1,04,1. 8,144.2,M,-30.3,M,19.0,0000*71
. . .
This data is normally not seen outside of the GPS mapping interface:So for fun, take Google Earth, find this location, "34 36.7743 N 086 34.0462 W" and see what Google Earth sees as the altitude:

• 189 M - Google Earth
• 144.2 M - raw GPS altitude

Two minutes later, I'm reading nine satellites at "34 36.8331 N 086 34.0270 W":

$GPGGA,090527.352,3436.8228,N,08634.0259,W,1,09,1. 2,188.9,M,-30.3,M,307.0,0000*43
$GPGGA,090528.352,3436.8331,N,08634.0270,W,1,09,1. 2,189.3,M,-30.3,M,307.0,0000*45

Comparing to Google Earth:

• 187 M - Google Earth
• 189.3 M - raw GPS altitude

The GPS longitude and latitude data was dead on for both locations. I had filled up with gas at the Shell station at Hobbs Road and Memorial Parkway (Rt. 231) and started driving to Hickory NC. One thing I can assure you is there was not a 45.1 M change in altitude in that short distance.

Once the GPS mouse has gotten more than 5 satellites, the altitude changes seems to settle down to +/- ~5 meters. Although not as accurate as a barometric reading, it is enough for energy studies at highway speeds.

Bob Wilson

 

You are right in that leaving out, "Why do you think. . ." is important.

I personally do not think elevation gained or lost while driving is important, and perhaps Toyota felt the same way.

However, when I'm riding my bike, I do want that information and Garmin has put a ". . .barometric altimeter for extremely accurate elevation and vertical profile data"

As pointed out in another post, a barometric altimeter is very accurate.

 

OK, OK...

X, Y, or Z; A, B, or C, now we all agree that a manual calculation is a must for our database. All of us here are putting up every effort to reduce the environment impact.

And remember, the most environmental concious individual has the lowest total gasoline consumed. I'll take a public transportation whenever possible even we have hybrids.

And I became a vegetarian since 1994. Maybe that's too far...

 

I'm not sure what you are saying here.

Regardless of what another post says, there can be issues with using barometric pressure to calculate the altitude. If you are measuring the barometric pressure at sea level, it can easily vary from 28.6 to 30.7 inHg due to the weather. Relying strictly on a barometric altimeter, this would correspond to ~1,100 ft above or ~600 ft below sea level. How does the barometric altimeter on your bike take the pressure changes that arise from the weather into account? Maybe crude wasn't the right word, but there are real issues here.

 

I don't recall agreeing to that. The point I made was that there is no proof here that what most people here are referring to as a "manual calculation" is any better than the display fuel economy.

 

Qslugs, do you have a ScanGuage? I would be interested to know if the sensor is off or if the gauge is the culprit. In my case the two sort of cancel out and my gauge reading is acutally pretty close, but a little optimistic. The sensor seems to output a lower value, but the gauge reads high. I too, have always used a raw calculation rather than trust the gauge. Oddly enough, the manual calculation sometimes disagrees (small amounts in both directions) with the automatic calculation on the website -- probably some difference in rounding values or similar.

 

Lucky you. . .No sarcasm intended. You have a developed public transportation system (I assume you live in the City and or boroughs). I grew up in Chicago where everything was a streetcar/bus, El ride away.

SoCal is different. I ride a bike, but recreationally, i.e. I don't shop with it, for example.

But back to display and calculated mpg. For whatever reasons, that display doesn't match up with the calculated mpg, and it seems to overstate the mpg. I think the originator of this thread said by 5 mph. Mine seems to be around 1 - 1.5 over, but as much as 5 mph under.

 

It doesn't. I do live a couple of miles from the ocean. Some days as I ride down Pacific Coast Highway with a wetland on one side, and the ocean around a bunch of yards on the other I smile as the elevation read-out tells me I'm under water.

I bought this device because it did have the barometric altimeter. And if I were flying with it, i.e., my life depended on a spot on altitude reading I would make sure I could calibrate it.

However, if all I want to know how much my elevation gain was over the distance of, at most, 100 miles, this is good enough.

So, how important is that information (elevation gained/lost) in calculating my Prius' mpg? I don't think - to me - it is important. In the case of the bike's instrument and the Prius', the information generated is beyond my control.

In other words, I can't control the elevation over which I travel, but in a way I can control my gasoline consumption.

On the bike, it's for amusement. "Boy, on that 28 mile mile ride through the canyon, I experienced 1770 feet of climb."

But do that in the Prius? Who cares? And after knowing that info, what does it tell me about increasing my mpg beyond just knowing I'm driving hills, rollers or mountains?