https://in-the-sky.org/satmap_worldmap.php
Was listening to a surveyor at dinner the other evening. He was insistent that a clear southern horizon is necessary for good gps sessions- North America; latitude 34. My gps experience is just starting and I haven't had a chance to quiz him on it.
So, I did a search and found the linked site. No assertion that the info is accurate but, pretty cool. You can toggle the types of satellites it plots in the 'select satellites' drop down.
From a plot of nav satellites (gps, glonass, galileo, beidou), doesn't seem like any particular cardinal horizon would out-perform another given use of a fully enabled receiver.
Insights, thoughts, facts appreciated. TIA.
It depends.... that used to be the gospel and still is fairly solid advice, especially if using legacy equipment?ÿ
Not all systems are equal.
High end systems are generally best.
Javad has a system that is top of class. Imho
N
The advice at NGS is that the sky should be visible from 15 degrees above the horizon in all directions, with minor exceptions for poles or small trees.?ÿ South is the most important direction for most of the US.?ÿ
https://www.ngs.noaa.gov/marks/descriptors.shtml#visibility
https://www.ngs.noaa.gov/AERO/Genspecs_A/Volume%20A_Attachment%2011-19.pdf
In my experience, you can push that somewhat and get usable results with greater obstacles (i.e., a larger trees), but any serious deviation will impact the accuracy to some extent.?ÿ Longer sessions make up some of the accuracy loss, but not all of it.
https://in-the-sky.org/satmap_worldmap.php
Was listening to a surveyor at dinner the other evening. He was insistent that a clear southern horizon is necessary for good gps sessions- North America; latitude 34. My gps experience is just starting and I haven't had a chance to quiz him on it.
So, I did a search and found the linked site. No assertion that the info is accurate but, pretty cool. You can toggle the types of satellites it plots in the 'select satellites' drop down.
From a plot of nav satellites (gps, glonass, galileo, beidou), doesn't seem like any particular cardinal horizon would out-perform another given use of a fully enabled receiver.
Insights, thoughts, facts appreciated. TIA.
You could use this site and obsruct the south to see how it affects your DOPs:
?ÿ
?ÿ
The GPS satellites are in six orbital planes that are at a 55 degree angle to the equator, meaning that no satellite ever passes directly above the north or south pole - the idea was to have at least four satellites in view at all times in all of the populated lands. So there's a "hole" in the constellation above the horizon that gets larger the farther north you go. It's for that reason that we were always taught that if you had to have an obstruction try to be due south of it.
I don't know what the orbits of GLONASS and Galileo are like; it may no longer matter with multi-constellation GNSS.
One thing to not do that I have seen some users do...
Do NOT put the point on the south side of a large solid object (water tower, tall building, etc), it WILL cause multipath. I have seen extreme examples of this, like a point almost underneath a large metal water tower, on the south side. I asked why, they said they were told to always put it on the south side of any blockage...that north did not matter...
A clear northern sky view is more important than a clear southern sky view. There is almost always enough satellites visible to the South that a 20?ø or partially blocked horizon can be overcome by other satellites. Sometimes to the North, satellites are only visible low or high in the sky.?ÿ?ÿIt is those low ones that help the most with the geometry.
Paul in PA?ÿ
Android app GPS Test and/or my Garmin GPSmap 60CSx have a screen that lets me know what is in the sky and as a check to see if my is connected and to compare signal strength.
The collective positions can form weak geometry at times and PDOP will get bad at times and locally from 11am till 1pm can become bad reception periods.
Thanks to everybody for the comments and insights. Southern exposures aside, I'll be bookmarking some web pages and trying to be more diligent with pre-field planning.
Feeling a little more confident that southern sky is not necessarily as strong a concern using 4-constellation gnss in my locale, the comment about being more attentive to the northern sky makes sense to me.
So, a subsequent question if I'm correctly understanding @paul-in-pa : For gnss surveying, I was unaware of the need for good satellite geometry in terms of 2d orientations (spread of satellites in xy plane). I thought variability in 3d can afford solid geometry even in situations where available satellites are grouped in a particular quadrant of the sky ( you can still have good triangles in the xz or yz planes)?
I accept that increased strength of position should come from good xy and xz/ yz?ÿ geometry, simultaneously; however, I did not consider that I should expect a statistically significant error if satellite spread is only in the zx/ zy.
checking in and checking out. Again, TIA.
?ÿ
?ÿ
?ÿ