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Joe only looks at DOPs chart and weather report for mission planning. Moe looks at both DOPs chart and Sky Plot and weather report. Is Joe missing out on something relative to Moe in terms of predicting accuracy in the field?

http://www.trimble.com/GNSSPlanningOnline/#/Settings

Note that there is a function to add obstructions or change cut-off elevation value in Settings, which affect both charts equally.

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The various measures of DOP are probably sufficient for any reasonably flat terrain, and knowledge of satellite positions isn't adding anything. In fact, looking at a snapshot of satellite positions is less useful for planning than the plot over time (where you can see the times where DOP is going to be bad, and you can take a lunch break or relocate sites).

Note the caveat about flat terrain though. If you have uneven terrain (effectively asymmetric cut-off angle), such as a mountain range or urban canyon, and you know that there will be a particularly difficult position to work, then you might be able to use the sky plot to work a "probable DOP" for that particular site. For example, if you have a mountain range running east-west, then at the time shown in the sky plot above, you are probably better off to be on the north side of it than the south side. You can't figure that out from the DOP plot alone.

You also might be able to apply that logic to some particularly uniform multipath situations (e.g. working around aircraft hangars, or near Stobie Poles), but I'm having trouble finding a scenario where you could do anything with the information that would be more useful than "it'll be a problem, lets take the choke ring antennas", which you probably would do anyway. As a contrived example, if you knew that you had a case where you get strong multi-path from a particular object (say the Stobie pole, which is close to a corner reflector on the ends where the steel U shapes are; or a flat metal wall like an aircraft hangar), you might be able to avoid the worst case situation where there are many satellites positioned at a reflecting angle (say where the line of poles runs north-south, or the hangar wall is east-west, for the sky plot shown in the question: PRN 6, 16, 27 and possibly 3 are going to be bad if you're north of the poles or north of the wall).

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  • I could only take the snapshot for Sky Plot but the actual website allows one to vary the time (bottom-right of Sky Plot). It seems that, if I have a particular point in mind, the mountain range situation can be resolved with Define Obstruction Curtain in Settings (screenshot added in the main question). However, if a project requires me to collect on both the north and south sides, I can see Sky Plot helps deciding which side to collect for the day, when to switch sides if that makes sense, etc.
    – user24397
    Dec 14, 2013 at 0:18
  • Could you clalify on the last paragraph: If I do not have the choke ring antennas, how can I reduce multipath with information on Sky Plot?
    – user24397
    Dec 14, 2013 at 0:19
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    I added a couple of fairly contrived examples. Not sure how that is going work in reality though.
    – BradHards
    Dec 14, 2013 at 2:53
  • My first comment says "if a project requires me to collect on both the north and south sides, I can see Sky Plot helps deciding which side to collect for the day, when to switch sides if that makes sense, etc." But now I guess that setting up Define Obstruction Curtain for both north and south side cases and looking at DOPs chart is better because it gives more precise estimate.
    – user24397
    Dec 14, 2013 at 21:03
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    The obstruction curtain might be an alternative to the sky plot, but it might get complex in some situations, so you might be better off looking at both (which was your original question).
    – BradHards
    Dec 14, 2013 at 22:45

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