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

[kirk]

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 Cadieuxhttps://gitlab.com/njacadieuxLe 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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