I just recently purchased two Locus Receivers and software. The first time I used the receivers I did a total system reset like the book said and then I let them gather data for 25 minutes (like the book said) then I cleared the memory and let them collect data. Both receivers locked on (green) to 6 or 7 sattelites. It took approximately 40 minutes before the hour glass blinked green. I'm working in a square mile or less area. Do I have to occupy points until the 1st light blinks green when working in this size of an area? I trimmed 20 minutes off the end of the 40 minute occupations and had no degradation of accuracy. I probably answered my own question, but would like some confimation from other users.

Mike J.,

I look at it kinda like this.

I am a 10 min or more drive from the office. If I cut off the receiver before it blinks green then I'm not sure of my data until I process it.

It's bad. I now have to drive back 10 min or more, setup the units again, 10 more minutes and then wait at least 15 min. more or less (best case). Now I have to drive back to the office 10 min or more. This extra trip just cost 45 minutes (best case) to save 20 minutes first time. This doesn't count wasted processing time spent finding out the first trip was bad.

I'd wait for the first blink myself.

jimbo

Jimbo,

I'll subscribe to that theory, kind of like insurance and "if that is enough then a litle more should be better" approach.
But then you have to determine which is the more feasible way to go. If the sats are few and far between with good PDOP levels, and its not too hard to run a conventional traverse, then I'd get a few static points to the site and run the rest with the total station.
But I still can't run a traverse with "good" trig levels for 5 km in less than say 17 minutes. Like they say, "speed cost money, how fast do you want to go?".......spend the time waiting on the occupation timer with a grin wondering where your competition is with their $50K RTK system running "control" in the RTK mode, and wondering what time tonight they will call and ask YOU "what have you got for an elevation at XXXX?"
Modified By Dave Huff on 3/20/2001 at 10:37 PM

Ashtech specs say one blink on the time light is sufficient data for a 5km baseline, two for 10K, 3 for 15K and solid for 20K. This light is a combination of # of SV's, PDOP and time, as I understand it.

I tell my customers to wait for one extra blink just to be safe, maybe some of the other Ashtech folks will tell me I'm wrong.

The most expensive part of your survey is getting to the point and occupying it (actually the most expensive part is going back and reoccupying it!). At the end of the day, the loss in efficiency is in my mind offset by the peace of mind gained in knowing you have solid solutions on your points.

I would be interested in hearing from some Locus users and their experiences on this.

Mike,

I'm with you on this one. I wait the "extra" light out because with good PDOP and 8 sats it is usually about 6 minutes more. Worse case, with 5 or 6 sats, it is about another 15 at the most.
Experience in the processing software will show you when you have a "good" solution; in the first days using the system a processed error of say 0.4' in a 10 or 15 km vector didn't appear to be so bad. But I've got a mindset now to go by, "let redundency cull your data"!
Oh, by the way, tell Cindy to call me, ok?
Modified By Dave Huff on 3/20/2001 at 11:02 PM

Mike,

I agree. Since I only set static control, I allow more than enough time for thorough data collection. For a pair of points, I'll allow an hour. If I can hit 20k light, that's what I'm looking for. Can't always do it in an hour, but 15k is normally sufficient. I still have questions about the time/data quantity considered to be proportionate to the length of vectors measured. I can't put my finger on it, but something keeps telling me the shorter lines actually benefit much more than the longer lines when given greater data collection times.

J.D. Billings, a Locus user that is anxiously awaiting the return of three units.

Mike

I'll "almost agree" on the extra light.
Ive found if I have 8 SV's and good PDOP I pick it up after the first light (90% of what we do is less than 5 Km) but..if the site is obstructed (tree limbs, leaves to one side) I let it go to solid, and this usually works out.. by the time you shuffle tripods, look for pins etc, their done. We don't (can't) locate everything with the locus but use it to set the controls that we trav off of later.

BTW JD .. what are they fixing on your three units??

Steve

Hey guys,

I also subscribe to the extra blink and solid in the trees practices.

Running kinematic with the system I have cheated on the re-inits after the alarm, like using 5-10 minutes on an unknown point for a re-init, but on static I always go with the recommended procedure or more.

Once I stretched the 12mile limit to about 15 and later x-checked with leap-frogging units. Worked out within a coupla tenths. Always kinda wondered if it was accidental that it came in this close or not? any thoughts ?

Jimbo

PS. We weren't doing anything that needed to be "tight" when we cheated.
Modified By James Webb on 3/28/2001 at 2:44 PM

The "beep" does a pretty good job at estimating the time for a good static shot.

Keep in mind that if you have no sky obstructions, you probably have the data you need in much less time, but that if there is one tall pine nearby, you better sit for another 20 minutes.

This has been my experience.

When the number of sats are 8, and the sky is clear, you have a lock in 8 minutes, at best.

When the sats are 6, and one tree stands nearby, you may have to sit for 45 minutes for the beep. It may be that you had the thing dialed in 12 minutes, but you just don't know. It may actually take 45 minutes or more.

You will get a "feel" for this over time.

Sometimes you have to be patient, and sit for an extra 5 minutes, to be sure.

This teaches us to take good notes again.