[Qgis-user] (no subject) (elevation question)

[Nicolas Cadieux]

Hi, 

Thanks for the precision.  So they are basically prone to the same problem (which is reassuring).  My guess is that the true befits is that they add a compass with the barometer so you can take a heading reading when not moving... I guess that is worth 100 bucks!  

Guess we’re moving away for the topic here... shitty ADHD! :)

Nicolas Cadieux
https://gitlab.com/njacadieux

> Le 21 avr. 2021 à 08:26, kirk <kirk at nortekresources.com> a écrit :
> 
> 
> Hi Nicolas.
> 
> You can set the barometer my using a known point and elevation or by setting the current atmospheric pressure. As with an anologue altimeter, your readings will change throughout the day as the pressure changes. This is less of a problem if you are out on a sunny day with a high pressure cell with a small pressure gradient. but becomes bit more problematic if a low pressure system is moving in.
> 
> 
> Sent from my Galaxy
> 
> 
> -------- Original message --------
> From: Nicolas Cadieux <njacadieux.gitlab at gmail.com>
> Date: 2021-04-21 9:14 a.m. (GMT-04:00)
> To: David Strip <qgis-user at stripfamily.net>
> Cc: Qgis Users List <qgis-user at lists.osgeo.org>
> Subject: Re: [Qgis-user] (no subject) (elevation question)
> 
> Hi,
> 
> Interesting but I very much doubt they are not applying a geoid  on top of the ellipsoid. If they can put maps of the earth on the device, they can put a geoid with a posting of 15´x15´! 
> 
>  I have been wondering about those barometric altimeters GPS for back packing.  I have a none electronic altimeter with me normally but it only really good if you consider the temperature changes.  
> 
> Nicolas Cadieux
> https://gitlab.com/njacadieux
> 
>>> Le 20 avr. 2021 à 23:03, David Strip <qgis-user at stripfamily.net> a écrit :
>>> 
>> 
>> In the course of trying to find what geoid model Garmin uses, I found this on a Garmin support page:
>> . It is not uncommon for satellite heights to be off from map elevations by +/- 400 ft. Use these values with caution when navigating.
>> Apparently some, but not all, models of the Garmin64 have a barometric altimeter. Depending on your actual model, this may or may not apply.
>> 
>> 
>>> On 4/20/2021 8:23 PM, Nicolas Cadieux wrote:
>>> Hi,
>>> 
>>> David gave you a very good answer. Your looking at a 11 meter difference.  That is not much.  The first thing would be to look at the gps measurement.  (Any trees? Good satellite constellation?  Any obstacles?). At best, your looking at a 6 to 10 meter error  vertically. SRTMs are affected by trees.  That would make the SRTM higher (not your case).  Last thing to look at the the differences between the gps geiod model (a model of the average sea level).  SRTM use EGM96.  Your GPS probably uses something a bit more modern. You can easily get a 5 meter error between two Geiods.
>> 
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