Just got my R8s Base/Rover combo and i need some help setting up and start experimenting.
-First off, in cases where i know the Grid and projection of my current project, there is no need for localisation right?
Also, is localization and ground calibration the same thing? Here it says it is, but here it says its another thing.
-Ok so imagine this. I just took the rover on the roof of a building to have a clear view of the sky. I set Grid/projection/units and geoid and took a peek on Grid coordinates. It wasnt a benchmark so there was no testing the accuracy of the solution, and also i hadnt connect to a base or network RTK, it was an SDGPS autonomous solution. But i immediately noticed something weird. The Elevation was -22m. I was close to the Sea but i was looking something more llike +15 or +20m. Isnt 40m elevation error way off, even for an autonomous solution. I was tracking 13 sats by the way.
So would you say this was the solution not getting corrections, an incorrect geoid file or the fact that the unit was not perfectly level?
BTW how can i check if i have a localised geoid? I live on Greece and EGM2008 is used. I used EGM96 Global instead though.
-An unrelated question is, if i do static, or base/rover RTK do i need to track SBAS? Or is there any reason for SBAS?
The SBAS system uses L1 only, which helps to improve the Autonomous position. I nit certain it can be used in RTK or post processing.
For the basics of RTK see thread https://surveyorconnect.com/community/threads/gps-mistakes.328963/
Do you have a geoid model set up in your data collector? That could easily throw you off 30 meters.
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Sounds like he has an automous position.
I know The post must have been boring being that long, but there was no way i could have given all that information and also been brief. Here it goes again.
Jason Graves, post: 402278, member: 9531 wrote: Do you have a geoid model set up in your data collector? That could easily throw you off 30 meters.
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therock003, post: 402271, member: 12282 wrote: So would you say this was the solution not getting corrections, an incorrect geoid file or the fact that the unit was not perfectly level?
BTW how can i check if i have a localised geoid? I live on Greece and EGM2008 is used. I used EGM96 Global instead though.
leegreen, post: 402280, member: 2332 wrote: Sounds like he has an automous position.
therock003, post: 402271, member: 12282 wrote: ....and also i hadnt connect to a base or network RTK, it was an SDGPS autonomous solution.
I don't know about Greece. Around here Eastern US, New York state, the Geoid Height is about -30m. When I see GPS derived orthometric elevations 30m below the theoretical elevation, the likley problem is wrong Geoid. So it sounds like you have the wrong Geoid, and an autonomous position. Which means a Double wammy that creates lot's of error. Without the GEOID you will be closer to the Ellipsoidal Height.
I suspected as such. Does anyone know how i can localise my geoid for use with my Trimble units (.GGF)? Carlson has a utility X-port which does that, but since Carlson does not support new Trimble units i'm using Survey Pro on the Collector and i need to localise it on the provided .ggf format.
I managed to get a valid geoid file for my area, but i'm using survey pro DEMO for windows and i dont see any option to import it into the program.
therock003, post: 402289, member: 12282 wrote: I managed to get a valid geoid file for my area, but i'm using survey pro DEMO for windows and i dont see any option to import it into the program.
You can't HELP those that won't help themselves.
You need to commit and purchase full version. Or at least have dealer give you a 30 day license with some direction and support.
Finally figured it out. You were right you cant help someone, he only needs to help himself 😉
Was it the geoid issue?
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Without a Geoid model loaded that covers the area where you are running the receiver, the heights you get are ellipsoid elevations, which will always be low by about the amount you mentioned.
No one's GPS receiver I am aware of will give you a precise position without a source of correction data. So while it may have been an interesting and illuminating trial of the receiver in SDGPS mode, that will never suffice for precise positioning.
JerryS, post: 402483, member: 205 wrote: Without a Geoid model loaded that covers the area where you are running the receiver, the heights you get are ellipsoid elevations, which will always be low by about the amount you mentioned.
No one's GPS receiver I am aware of will give you a precise position without a source of correction data. So while it may have been an interesting and illuminating trial of the receiver in SDGPS mode, that will never suffice for precise positioning.
Hate to nit pick here, but.
Ellipsoid HEIGHTS or not technically "elevations," but that might be an esoteric distinction. Personally, I think that the term "elevation" can be misleading, but that's just me.
More importantly, the GEOID can be either ABOVE or BELOW the surface of the Ellipsoid, depending on where you are on Earth. It's true that the GEOID is "always" below the ellipsoid here in conus, but some folks who post (and I assume read) here, are not in conus.
Just saying.
Loyal
Thank you for the correction. I know that we tend to use terms interchangeably that are not really the same thing. But hey, my degree is in tractor driving...
An autonomous setup like a static raw data solution has a very variable elevation. It can easily be .100' +/- but usually high. A poor elevation can also affect your vector solutions. You can greatly improve it by using an elevation from a USGS quad map if you are in an ortho system. The only way to get a truly good elevation is to occupy a benchmark or have CORS data and control, OPUS-S, OPUS-RS or post process your self. If you do not have any of those capabilities, you are merely a button pusher.
-22m is not weird. Consider that in most SPC systems any seacoast is well removed from the control coordinates and that the coastal geoid is equally above or below the ellipsoid on an earthwide basis. I learned very early to write it out before doing the math and to compare it to a nearby benchmark datasheet, whether I could occupy that monument or not, the ellipsoid geoid spread should be similar.
Paul in PA
