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

[Nicolas Cadieux]

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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