that will take a Rinex file and show a kinda "post-processed" planning window of the sats?

In Magellan's MSTAR I can zoom into the file times window and see all the gaps and see how they lasted etc.

BUT . . . what I'm thinking is to be able to see how all the sats relate to one another in a "map" similar to A.S.'s sky plot.

AOSS did this. I believe GNSS now does it. Somebody correct me if I'm wrong.

Tommy McClain

John, Open Planning with your project coordinates, and put in the date of your observation, set the correct time zone, and make sure you have a recent almanac. Shrink the time window, to your observation times, then click on the Sky Plot.

Solutions is a very powerful tool for the money. GPS Planning is a separate but useful tool, for no extra money.

Paul in PA

Are you saying Paul, that the Sky lot will show my observations, with the gaps and and all?

I want to reconcile my observation on the session and THEN use that to make an obstruction mask for another day.

I really think what you're refering to is nothing more than the simple sky plot based ONLY on an almanac.

I guess I misunderstood your original question. I thought you meant showing a bar graph in time mode that showed all the sats and where all the gaps of missing data were. AOSS did this and this was where you could actually exclude portions of the data. I see now that that's not what you're wanting.

I can see the benefit of what you are requesting. I've also wantedsimilar, but I took it from a different view. How about setting up a panoramic digital camera on the tripod. Use the resulting digital photo as way to create an obstruction mask in the planning software. I could see Ashtech selling such a camera as a seperate accessory along with the GPS receiver/antenna.

Tommy McClain

As I said Solutions is a tremendous value for the buck.

What the heck difference is it going to make? Do you plan on going back and shooting things from the sky?

The sky plot comes from the almanac, it is showing you where and when your is supposed to be. An obstruction mask is a lot of work, it is almost always easier to set up somewhere else nearby and getting additional or different data.

If you have obstructions greater than 15° elevation and cannot competently sketch them on a sheet of paper, how did you get licensed in the first place.
You have to use your brain in at least 4 dimensions. X, Y, Z and t.

You have your raw data, which is going to give you the time, so even if all you have is a pencil and paper you can figure out when the bad data is. I just set a planning window to 15 minutes of time with 5 minute markers. The satellites do not move far enough to really differentiate between the markers so I will leave it at 15 minute markers where it has always been. So now I know where the satellite was when it had bad data.

In reality for any one satellite to contribute 20 minutes of data is great, even if it is only 5 minutes here, there and somewhere else.

If the data is absolutely bad Solutions will drop that satellite from the computations. What is the PDOP and number of satellites on the vector in question.

John, I think you try to create problems where none really exist.

Paul in PA

In the olden days of short GPS 'observation windows' and smaller constellation, we used to do site reconnaissance prior to the GPS work. This involved, among other things, scouting proposed GPS site locations to assess access and site security, locate existing control, and to create obstruction plots. A plot was simply a circular graph on paper representing the available sky view in the cardinal directions around the site. We used a compass and a clinometer to observe and record on the plot any obstructions that might affect the observation data - tree lines, buildings, etc.

Back in the office, we could add this obstruction mask data in the mission planning software and determine what times during the available observation window would be best for visiting a given site.

To this day, this low tech approach is probably still the best, easiest and most accurate way to build sky view 'obstruction masks' at a given site.

You know, I've been giving a lot of thought to starting up an Internet based, product independent GPS technical support and project admin site. One of these days I may just do that.

Modified By Scott Partridge on 12/2/2004 at 1:46 PM

With the better constellation, in general it is less critical than in the past to do so before heading out on the job. If you encounter a potential problem, it can be dealt with in the field. I guess John does not want to take advatage of his time in the field to make an obstruction sketch, for future work.

Several key points about an obstruction. If there is a major obstruction in the SE say, you do not want to use a control site that has great SE sky and an obstruction elsewhere. That scenario can block out satellites from 2 quadrants, cutting down your common satellites to too few. In essence you have built yourself a wall.

If you have to occupy a site with a SE Obstruction make sure your control site has the same clear sky as your problem area. Then use planning to find the time when your clear sky area is overloaded with satellites. Off hand I would say that 8 satellites in 3 quadrants can get you the same area of precision of 6 satellites in 4 quadrants. It becomes more important to have them spread high and low, a good geometric figure can be created.

Few obstructions are so big that getting a second observation within line of sight of the first cannot clear the obstruction. One of those few would be the rocky mountains. A second point observed concurrently or even not can save a required bad position. When they are that bad, planning can generally take place in your head because we are talking many tens of degrees not less.

What John wants to do is to be able to download a LIDAR grid mesh of his site, have it automatically create a mask so that he does not have to think about what he is doing. That is all feasible, for tens of thousands of dollars worth of software and additional time. I can take all that money and buy an extra cup of coffee while I just wait a little bit longer to collect some extra data.

I had a college instructor talk about the future and it was a Dick Tracy wrist watch GPS, total station cappacino machine all in one. Maybe John should have taken that class.

Paul in PA

?
Modified By Lawrence Paul Lopresti on 12/2/2004 at 2:07 PM

To be frank (not Frank Morski), in the last 20+ years of doing GPS almost daily, I haven't done mission planning or built obstruction plots for a long long time. Well, there was that one time back in 1993 when I was doing a first order control survey within a large oilsands development and it was part of the project requirements. Heck, that is still a long time ago.

We put up our receivers in some of the most GPS hostile places you can imagine but I do not do any mission planning other than getting a feel for the optimum observation times on a given day when working in these places.

I don't stop others from doing it. You can learn a lot of useful stuff going through the procedures.


Modified By Scott Partridge on 12/2/2004 at 3:59 PM

I couldn't afford to buy one if there was. Probably would not use it if it was given to me, because of the resources it would consume.

I am like you Scott, I do some preplanning, but almost never does the ptimum timing work out. Once the unit is on, the sky view tells me what is going on, and my little preplanning tells me if it is going to get better or worse.

In Calgary, the satellites are barely overhead, but how good are the satellites peaking over from the NE and NW? I did a planning session for you and early this morning there was a time with only 4 satellites in the sky. Good time to stay in bed. Where you are GLONASS would be very helpful, satellites a bit farther North and some peeking over the pole.

Paul in PA
Modified By Lawrence Paul Lopresti on 12/2/2004 at 4:27 PM

Not in Calgary this week. I'm up in beautiful Rainbow Lake, Alberta providing supervision of a GPS project in the area of 58°47'N, 119°52'W.

All helicopter access and the weather has been forgiving.

Actually, satellite coverage is quite good up here with the exception of about an hour from 2:30 to 3:30 in the afternoon.

That is the only mission planning I did.

You are Mountain Time right? It looks to me as your worst time today was 12:45-1:15, there 8-6 sateliites but PDOP hits 8.5. Was it actually that bad? I see 0 satellites NE of your location.

They have satellite 02 scheduled off, yesterday, today and tomorrow to park it in final position near 24. 24 is scheduled to be turned off tommorow. They will probably turn 02 on before turning 24 off. Don't know if they have enough fuel to move 24 someplace else, or will just let it drift.

With 02 off I see a PDOP of 2.0 at 3PM.

Paul in PA

I had forgotten how long this job has been going on for.

Yep, Mountain Standard Time (-06:00 hr)

The hole in the coverage is actually about 1:30 to 2:30 PM now. It's advanced about an hour since the job started. Not a lot up there at that time. Just before 10:00 AM isn't great either but it takes until about 10 anyway to get out there and the receivers up and running. The helicopters can't fly until 'legal' first light which right now is about 8:45 AM. They have to be back on the ground at camp by 4:15 PM. It makes for a short work day.

The terrain is quite flat, mostly frozen muskeg with short black spruce and tamarack. There are some stands of 20 to 30 metre poplar trees but it is reasonably sparse.



Modified By Scott Partridge on 12/2/2004 at 7:14 PM

I am Eastern Standard Time -5hr.
Central Standard Time is -6hr.
Mountain Standard Time should be -7hr.
Mountain Saving Time was -6hr.

You been in the cold too long?

Yep... lol. My fingers can't hit the right keys anymore...

Hey, the offset was -6 when I came up here! ;-)

Modified By Scott Partridge on 12/2/2004 at 10:35 PM