Jump to content
Sign in to follow this  
Followers 1
Team CowboyPapa

GPSMAP 64st Elevation Determination Methods

Recommended Posts

While not directly related to geocaching, I am posing this question here as I have not received answers after posting on other forums.  After reading the user manual for the Garmin GPSMAP 64st, I could not find an answer in specific detail to my question below.

 

1.  I have a Garmin inReach Explorer+ Satellite Communicator which has two methods of user selectable elevation determination, whereby both use barometrically derived ambient pressures:

1.a.  One option, auto-calibration, uses the GPS derived elevation data to calibrate, or adjust, the elevations determined by interpolating the pressure vs. altitude data.

1.b.  The other, non auto-calibration, presents elevations determined solely by interpolating the pressure vs. altitude data.

2.  Also, I have a DeLorme Earthmate PN-40 GPSr which has a third user selectable method of elevation determination.  As such, when selected, it uses only GPS derived data without consideration barometrically measured ambient pressure.

 

My question is:  In addition to the two barometric options, 1.a. and 1b., does the Garmin GPSMAP 64st device have the third option, to display GPS elevation only (independent of ambient pressures), as noted in 2., above?

Share this post


Link to post
1 hour ago, Team CowboyPapa said:

[...]

My question is:  In addition to the two barometric options, 1.a. and 1b., does the Garmin GPSMAP 64st device have the third option, to display GPS elevation only (independent of ambient pressures), as noted in 2., above?

The satellite status page shows Gps elevation. There is also a data field "Gps Elevation". Please refer to your manual how to use data fields in Trip Computer or a Dashboard.

From the Manual:
Customizing the Data Fields
Available Data Fields
The User Manual

Hans

Edited by HHL

Share this post


Link to post

@HHL, I appreciate the attempt to help.

However, as I mentioned above:  " After reading the user manual for the Garmin GPSMAP 64st, I could not find an answer in specific detail to my question below."  So, again, from your reference, I see the same statement:

GPS Elevation

The altitude of your current location using GPS.

Again, as I mentioned originally, "...specific detail...", I do see "..using GPS.."  I do not see where the manual states that barometric is excluded, nor do I see where it mentions using only data from the satellites.

I was hoping that rather that get references from the manual that I stated from which I had already read, that someone could use their 64st to actually see if the third possibility, elevation values derived without barometric considerations is possible.
 

 

Share this post


Link to post
37 minutes ago, Team CowboyPapa said:

[...] I was hoping that rather that get references from the manual that I stated from which I had already read, that someone could use their 64st to actually see if the third possibility, elevation values derived without barometric considerations is possible.

The data field Gps Elevation DOES only uses the Gps elevation. You may easily test it it (I did it years ago) whilst traveling by plane. The barometric elevation is sticky at appr. 3000 feet (which is the cabin's pressure whilst flying) whereas the Gps Elevation data field shows the real elevation.
Have you ever guessed why the data field Gps Elevation is named as such?

Hans

 

Edited by HHL

Share this post


Link to post
42 minutes ago, Team CowboyPapa said:

@HHL, I appreciate the attempt to help.

[...]

Which part of:

GPS Elevation
The altitude of your current location using GPS.

do you not understand?

Share this post


Link to post

I appreciate the exact answer, thank you.  Actually, I did want to do exactly that, test in hand.  I went to two local stores, but neither had a demo model that I could test.

And, as you stated above:  "Have you ever guessed why the data field Gps Elevation is named as such?"

Yes, I did actually guess that such was possible, OTOH, I wanted certainty.

 

Now, if I had been asked the same regarding the PN-60 model, my response would have been:

1.  Holding it in my hand, invoking Device Setup, then Compass & Altimeter ..., I then see two, yes or no, check boxes, Enable Barometric Altimeter and Auto Calibrate Altimeter.

2.  Checking the Enable Barometric Altimeter would activate it and it would be used, unchecking it would deactivate barometrically derived elevations and elevations would be derived from satellite data.

3.  I both both boxes were checked the barometric elevations would be auto calibrated, but if only the second box was checked, the elevation would not be affected.

Share this post


Link to post
17 minutes ago, HHL said:

Which part of:

GPS Elevation
The altitude of your current location using GPS.

do you not understand?

Exactly, does that GPS refer to the Global Positioning Satellite data or the GPS handheld unit.

As I said it is non-specific in detail.

I would have said:  "The altitude of your current location using data from the GPSatellites.

Share this post


Link to post

The Garmin units uses both methods simultaniously, hence the reduced settings on just turning automatically barometric calibration On/Off.
It's up to you to select which of both values you're consider to see in a data field.

Hans

Share this post


Link to post
15 minutes ago, Team CowboyPapa said:

Exactly, does that GPS refer to the Global Positioning Satellite data or the GPS handheld unit.

As I said it is non-specific in detail.

I would have said:  "The altitude of your current location using data from the GPSatellites.

That's pretty nitpicking. I'm off from this point.

Share this post


Link to post

I really have to apologize for my overuse of specificity.  It was throwback to my prior activity as a member of the GPS launch team where I actually participated in the rocket launches of the GPS Block IIR satellites from VAFB.  They all seem to work in feeding the information to our handheld units; consequently, I don't appear to have made any substantial mistakes.  :D

Share this post


Link to post
17 minutes ago, HHL said:

That's pretty nitpicking. I'm off from this point.

Exactly, I agree wholeheartedly.  Everything we did in our rocket launches was exceedingly precise, or nitpicking as it might be described. 

For example, the first stage fuel load would be expressed as 7,258 gallons instead of 6500 - 8000 gallons.

Share this post


Link to post

You wouldn't (or shouldn't) be using a consumer handheld gps for your rocket launches because they're not that precise. That said, using the barometric altimeter will be more accurate as long as it is properly calibrated. 

Share this post


Link to post
15 hours ago, Mineral2 said:

You wouldn't (or shouldn't) be using a consumer handheld gps for your rocket launches because they're not that precise. That said, using the barometric altimeter will be more accurate as long as it is properly calibrated. 

I don't recall that I said that we used consumer grade handheld gpsr's for launching the GPS satellites.  The onboard guidance and control computers did all that. 

Share this post


Link to post

Another related question, or two, regarding elevation issues not mentioned in the manual:

1.  Waypoint generation - can either barometric or GPS elevations be selected as options?  If the user cannot select either as an option, which is used?

2.  Track generation - same question.

Share this post


Link to post
1 hour ago, Team CowboyPapa said:

Another related question, or two, regarding elevation issues not mentioned in the manual:

1.  Waypoint generation - can either barometric or GPS elevations be selected as options?  If the user cannot select either as an option, which is used?

2.  Track generation - same question.

It stores the elevation based on barometer only. The barometer elevation is calibrated with one of two settings.  Auto calibration On or OFF.  From what I can see it calibrates to the GPS within the first 15 minutes or so of the unit being powered up.

Edited by Red90

Share this post


Link to post
17 hours ago, Mineral2 said:

...... That said, using the barometric altimeter will be more accurate as long as it is properly calibrated. 

I agree, partially. 

If I wanted to measure the height of a hill that I could descend in five minutes during quiescent weather, I would specify non auto calibrated barometric for elevation.  Then record a waypoint at the top, one at the bottom and subtract bottom from top.

OTOH, recording a track on a week long back pack trip along the Pacific Crest Trail with a weather front predicted .............

Share this post


Link to post
22 hours ago, HHL said:

......... 3000 feet (which is the cabin's pressure whilst flying) ........

 

IIRC, when I validated the performance of cabin air pressure systems for commercial aircraft, the pressures corresponded to 6,000 - 8,000 ft.

Edited by Team CowboyPapa

Share this post


Link to post
11 hours ago, Red90 said:

It stores the elevation based on barometer only. The barometer elevation is calibrated with one of two settings.  Auto calibration On or OFF.  From what I can see it calibrates to the GPS within the first 15 minutes or so of the unit being powered up.

It stores elevation based on whatever method is turned on. If the barometer is turned off, tracks and waypoints will record the GPS elevation.

Share this post


Link to post
On 3/10/2018 at 4:32 PM, Mineral2 said:

You wouldn't (or shouldn't) be using a consumer handheld gps for your rocket launches because they're not that precise. That said, using the barometric altimeter will be more accurate as long as it is properly calibrated. 

No, the barometric altimeter will be more precise than the GPS altitude.  If properly calibrated, the barometric altimeter may be more accurate than the GPS altimeter because of the precision.  However, it is rare for a barometrically calibrated elevation to be more accurate than the GPS elevation for more than an hour or so.  And the barometric altimeter usually has a lag of 30 seconds or more.  Which is not a big deal hiking, but can be significant for e.g. rockets.

Edited by fizzymagic

Share this post


Link to post
9 hours ago, Mineral2 said:

It stores elevation based on whatever method is turned on. If the barometer is turned off, tracks and waypoints will record the GPS elevation.

How can you turn off the barometer?

Share this post


Link to post
10 hours ago, fizzymagic said:

........  And the barometric altimeter usually has a lag of 30 seconds or more.  Which is not a big deal hiking, but can be significant for e.g. rockets.

Unfortunately, the above is a complete non sequitur.  The altitude of a rocket in flight would never be determined from an onboard barometric source.  Think of the dynamic pressure as being proportional to the square of velocity.  Yes, putting your arm out the car window at 60 mph results in 4 times the aerodynamic pressure as at 30 mph.

Share this post


Link to post

You can measure static pressure in a moving object or in a flowing stream.  That is simple and very common, but a bit off topic.  Air speed is commonly measured by comparing the differential pressure between total and static pressure giving the dynamic pressure.

Back to the stored elevation data, unless I'm missing a setting, it always uses the barometric elevation in the waypoint data and track data.  Maybe Mineral2 can show me what I'm missing, but I just went through all of the settings.

Share this post


Link to post

I don't have a 64, and it sounds like the barometer settings are similar but different, but on my Oregon, if I set the altimeter settings to: Auto calibration - off; and Barometer Mode - fixed elevation then the unit will record and display the GPS elevation. I use these settings when flying and the tracks show altitudes of 35000 feet rather than the 6-8000 I would get when the barometer is set to variable.

Share this post


Link to post
1 hour ago, Mineral2 said:

I don't have a 64, and it sounds like the barometer settings are similar but different, but on my Oregon, if I set the altimeter settings to: Auto calibration - off; and Barometer Mode - fixed elevation then the unit will record and display the GPS elevation. I use these settings when flying and the tracks show altitudes of 35000 feet rather than the 6-8000 I would get when the barometer is set to variable.

Correct!

 

 

Share this post


Link to post

I appreciate the attempts posted here in order answer me question.  However, as a review of the above does not assure me of a specific answer, I am implementing a new plan: 

1.  I have gone to Amazon and posted the same question:  https://www.amazon.com/ask/questions/Tx1VLX1SQKW6VE8/

2.  If I decide to procure one and have not received an answer in which I have the confidence that it is correct, I will go to customer service Chat function and ask if I can return for full refund (inc. return shipping) if the device does not meet my requirements.

3.  Outside of that................................

 

Thanks again!

Share this post


Link to post
2 hours ago, Team CowboyPapa said:

I appreciate the attempts posted here in order answer me question.  However, as a review of the above does not assure me of a specific answer, I am implementing a new plan: 

1.  I have gone to Amazon and posted the same question:  https://www.amazon.com/ask/questions/Tx1VLX1SQKW6VE8/

2.  If I decide to procure one and have not received an answer in which I have the confidence that it is correct, I will go to customer service Chat function and ask if I can return for full refund (inc. return shipping) if the device does not meet my requirements.

3.  Outside of that................................

 

Thanks again!

Where have we not answered your question? The answer is yes, the settings can be made so that only the elevation returned back by the GPS satellites is displayed and recorded.

Share this post


Link to post
12 hours ago, Mineral2 said:

Where have we not answered your question? The answer is yes, the settings can be made so that only the elevation returned back by the GPS satellites is displayed and recorded.

Yes, I checked Mineral2's settings and it does display and record the GPS Elevation.  Team CowboyPapa has problems believing people.  I'm not sure of his purpose in asking here if he will not ever believe anyone.

Share this post


Link to post
4 hours ago, Red90 said:

[...] I'm not sure of his purpose in asking here if he will not ever believe anyone.

He is either rather ignorant and stupid or a Troll. Both qualifies an Ignore.
Done. ;-)

Hans

NB: I'm sorry being that harsh here. But the TO's behaviour is more than unfriendly to helpful people.

Edited by HHL

Share this post


Link to post

I mean, he did provide us to the amazon link. We can just answer his question there. :lol:

Share this post


Link to post

Amazon question and answers are known the world over as the most reliable source for factual information on the planet.

Share this post


Link to post
16 hours ago, Mineral2 said:

Where have we not answered your question? The answer is yes, the settings can be made so that only the elevation returned back by the GPS satellites is displayed and recorded.

My apologies, you stated above that you did not have a 64 and then went on to describe your Oregon...:

"I don't have a 64, and it sounds like the barometer settings are similar but different, but on my Oregon, "

Not directly describing how a 64st works from personal key pushing made it hard for me to accept.

Share this post


Link to post

yeah, I understand that. I just checked the 64 series manual and the altimeter settings are identical, as I expected. You'll find that when it comes to settings, Garmin is fairly consistent with structure from model to model, even across time.

Share this post


Link to post
On 3/10/2018 at 0:01 PM, Team CowboyPapa said:

Now, if I had been asked the same regarding the PN-60 model, my response would have been:

1.  Holding it in my hand, invoking Device Setup, then Compass & Altimeter ..., I then see two, yes or no, check boxes, Enable Barometric Altimeter and Auto Calibrate Altimeter.

2.  Checking the Enable Barometric Altimeter would activate it and it would be used, unchecking it would deactivate barometrically derived elevations and elevations would be derived from satellite data.

3.  I both both boxes were checked the barometric elevations would be auto calibrated, but if only the second box was checked, the elevation would not be affected.

Again, can someone, particularly those who denigrate my intelligence, provide a hands-on, step-by-step procedure with a 64st similar to that which I have just quoted above?

Share this post


Link to post
3 hours ago, HHL said:

He is either rather ignorant and stupid or a Troll. Both qualifies an Ignore.
Done. ;-)

Hans

NB: I'm sorry being that harsh here. But the TO's behaviour is more the unfriendly to helpful people.

Yes, it is my complete idiocy that prefers a step-by-step description in a how-to context.

Share this post


Link to post

Looking at the 64st, I see 9 buttons, one of which allows 4 options, for a total  of 12 selected pushes at a time.  As I could not gain access to one at a local retailer, I was hoping that someone here who has one could provide such a keypunch-by-keypunch, how-to, procedure to accomplish track recorded elevations not calculated from barometric pressures.

Share this post


Link to post

my instructions with the Oregon are identical to the 64s. That is how you effectively disable the barometric altimeter with a Garmin gps. You're not going to find an identical workflow to a DeLorme GPS because it's not designed by Garmin. But there is a homologous option.

Settings > Altimeter >
Auto Calibration > Off
Barometer Mode > Fixed Elevation

Setting the Barometer mode from Fixed to Variable turns on the Barometric Altimeter.
Turning Auto Calibration on automatically calibrates the altimeter with the GPS elevation at fixed intervals. You can always manually calibrate the altimeter at any time if you know the correct elevation and/or pressure.

Are we done? Do you still not believe me? The same steps are used with an eTrex 30. Or an Oregon 700, or an Oregon 450, or a Montana xxx, or a 62s, or a 78s. Maybe even with a 60csx.

Share this post


Link to post
4 hours ago, HHL said:

He is either rather ignorant and stupid or a Troll. Both qualifies an Ignore.
Done. ;-)

Hans

Whew!  What luck!  My ignorance did result in a launch failure of a Delta II rocket to put a GPS satellite in orbit.

I just can't remember which one blew up.

Edited by Team CowboyPapa

Share this post


Link to post
19 minutes ago, Mineral2 said:


Are we done? Do you still not believe me? The same steps are used with an eTrex 30. Or an Oregon 700, or an Oregon 450, or a Montana xxx, or a 62s, or a 78s. Maybe even with a 60csx.

OK, while not actually touching a 64st, I do accept it as implementation of traditional methodology.

Share this post


Link to post
4 hours ago, HHL said:

He is either rather ignorant and stupid or a Troll. Both qualifies an Ignore.
Done. ;-)

 

How lucky were those Boeing executives that required me to approve and sign-off on preflight documents sent to the launch sites VAFB and CCAFS.  Oh yes, and the Iridium satellites that the Garmin inReach Explorer+ communicates with.

 

Come back later for my next autobiographical lie!

Share this post


Link to post
41 minutes ago, Team CowboyPapa said:

Again, can someone, particularly those who denigrate my intelligence, provide a hands-on, step-by-step procedure with a 64st similar to that which I have just quoted above?

I have a 64S.  The settings are identical to what Mineral2 posted and they result in the GPS Elevation being displayed and recorded....as I posted earlier.

Share this post


Link to post
18 minutes ago, Team CowboyPapa said:

How lucky were those Boeing executives that required me to approve and sign-off on preflight documents sent to the launch sites VAFB and CCAFS.  Oh yes, and the Iridium satellites that the Garmin inReach Explorer+ communicates with.

And you do not understand static and dynamic pressure and that aircraft use a barometer for altitude calculations?  You would have thought an engineering degree would be a minimum requirement.  Scary stuff.

Share this post


Link to post
18 minutes ago, Red90 said:

I have a 64S.  The settings are identical to what Mineral2 posted and they result in the GPS Elevation being displayed and recorded....as I posted earlier.

Thanks!  I accept that in this regard that the 64s and 64st are identical.

Share this post


Link to post
17 minutes ago, Red90 said:

And you do not understand static and dynamic pressure and that aircraft use a barometer for altitude calculations?  You would have thought an engineering degree would be a minimum requirement.  Scary stuff.

I absolutely do understand such.

Another lie:  I had to approve the tested performance data for the LOX tank pressure relief valves for the 1st stage propulsion system of the Delta launch vehicles. Yes, that does require knowledge of barometric pressures as a function of altitude.  Addtionally, I do understand the for aircraft, the pitot tube is used to measure dynamic pressure for speed calculations.

Would you like another lie later?

Share this post


Link to post
On 3/10/2018 at 0:08 PM, HHL said:

That's pretty nitpicking. I'm off from this point.

Yes,  (I am not being supercilious here.)  It just came to me as a bolt of lightning.  I agree with degree of nitpicking totally; furthermore, what just hit me is why and how I was affected.  It will take me a while, but I will put it together and post back.

Share this post


Link to post
1 hour ago, Red90 said:

And you do not understand static and dynamic pressure and that aircraft use a barometer for altitude calculations?  You would have thought an engineering degree would be a minimum requirement.  Scary stuff.

Yes, I do understand them and I did make those calculations as part of my career.

Yes, I do have a BS degree in engineering from an outstanding, private university. ( OTOH, not inclined to take the diploma off the wall, scan it and insert it here.) Subsequently, I was hired into the aerospace industry upon graduation and worked there for 45 years. 

Share this post


Link to post

OK, here is my response to all the comments above regarding my background and engineering competency. Please accept these in one of two possibilities, it is 100% true or 100% lies.  As I post them, there is no in between alternative.

 

Yes, in my aerospace career I worked in aircraft, manned spacecraft and launch vehicle programs.  Specifically:

1.  Aircraft - Douglas Commercial and USAF Transport.  Designed the Environmental Control Systems (cabin temperature and pressure), Anti-icing systems and Hydraulic Systems. 

1.a.  Verified predicted performance of bleed air conditioning subsystem design (for the CFM56 engine upgrade to the DC-8-70) in the following two steps.

1.b.  Firstly, I rejected the supplier's original design as not functional between all flight conditions [0 mph at sea level and 600 mph and 40,000 ft]); they did not tell me that I was wrong and argue with me. 

1.c.  Then, I accepted their redesign, we implemented the redesign and the US FAA certified it, and nobody subsequently died of asphyxiation.

2.  Manned spacecraft - Skylab and Space Station.  Thermal Control, Heat Transfer Systems.

3.  Launch Vehicle Programs - Delta and Delta II.  Verified performance of 1st and 2nd Stage Propulsion Systems.  Delta II 1st stage length was 12 feet longer than the original Delta, resized the Lox and Fuel tank lengths accordingly.  Verified predicted performance of 1st and 2nd stage propellant tank pressures during flight.

Yes, I have understanding of ambient pressures and temperatures as a function of altitude and the relationship between static and dynamic pressures during all flight conditions.

 

OK, that was how I developed my professional behavior with respect to the level detail to which I work (or, my level of nitpickingitness).

 

Now, which I have just come to understand is that I continue to work in my now HOBBY environment to the level of detail in which I worked in my former professional career environment.                                                       

 

Lastly, as I now understand the greater level of detail to which I work here is different from others in this hobby environment, I do not harbor resentment regarding the terms to which I have been described, such as:

"... do you not understand?"

 " That's pretty nitpicking."

" I'm not sure of his purpose in asking here if he will not ever believe anyone....He is either rather ignorant and stupid or a Troll. Both qualifies an Ignore.""NB: I'm sorry being that harsh here. But the TO's behaviour is more than unfriendly to helpful people."

Are we done? Do you still not believe me? "

" And you do not understand static and dynamic pressure and that aircraft use a barometer for altitude calculations?  You would have thought an engineering degree would be a minimum requirement.  Scary stuff."

 

Yes, I am not upset regarding the nature of the above comments.  I do understand that they stem from an unawareness of how I had to comport myself in my professional aerospace engineering career and that I continued similarly in this forum.

Share this post


Link to post

It's just that geocaching, and even orienteering and wilderness navigation don't require the level of precision that engineering requires. If your hobby is geographic/geologic surveys, then you really want a professional grade survey device as you won't get the level of precision you desire from a consumer grade recreational handheld gps. There's a reason we suggest that when you get within 30 feet of a cache, you put your gps down and search with your eyes. And elevation data from the gps is even less accurate and precise than the surface positional estimate.

Nevertheless, several times we answered your question for you (a question which did not require any engineering level expertise) and several times you failed to believe the answer was given to you.

Share this post


Link to post

I don't see the issue here as being "nitpicking", but rather a lack of trust. Rather than accept the word of those who have used these devices for years and have even gone to the lengths of doing additional testing to confirm, you seem to be insisting on some kind of incontrovertible proof directly from authoritative sources. If that's the only thing that will convince you, then you've come to the wrong place. You'll need to talk to Garmin, but you shouldn't be surprised if you find you get far less useful information from them than you have here.

  • Upvote 2

Share this post


Link to post

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
Sign in to follow this  
Followers 1

×