Need help selecting a Static GPS for OPUS

I work for a County Hwy Dept which already has the County mapped in GIS under SPC.  I'd like to roughly tie my local survey work into it using a low cost static OPUS solution.  At one time, the NOAA site stated that OPUS-S solutions had to be L1/L2, is that still the case (http://www.ngs.noaa.gov/OPUS/about.jsp) because I currently only see specifics on Rapid Static solutions?

Thanks.

All 'flavors' of OPUS are strictly L1/L2 at this time. Occupation duration requirements are the only real difference between OPUS_S (2+ hours) and OPUS_RS (15 minutes – less than 2 hours). Well...there IS a lot of difference in the processing algorithms between the two, but that's a whole different discussion.

 

If you ONLY have L1 equipment, you could post-process to the local NGS_CORS, if you are in an area of relatively dense CORS coverage. I would hesitate to process L1 only to CORS in excess of about 15-20 kilometers though, and things can get tricky much past 10 km too. There is L1-ONLY post processing software available for free download out there.

 

Good (but old) L1/L2 systems (receiver & antenna) turn up on ebay all the time, and often can be had for $1000 (or less). I assembled a really nice system (antenna, receiver, cables, controller) for well under $1k last year (3 separate purchases), BUT I already had the requisite software (controller & binary-RINEX converter) to utilize it. Most (but maybe not all) manufacturers have free “to-RINEX” converters available for their equipment, but I would verify availability (and connectivity) before buying anything.

 

Loyal 

  

Thanks.  I downloaded NOAA's powerpoint file on OPUS and also caught that it was still L1/L2 for static.  My old company had picked up a demo Sokkia GRS2200/2300 (really a rebadged Astech Z) which we used for RTK and static work using OPUS.

I'm fairly certain we don't have good CORS coverage to get by with just L1.  We used to use OPUS to resolve our work in Central Illinois to sites from Rock Island, Springfield and Champaign.  Is there a place I could check, using just L1 is new territory for me.  I did find this on BLM's website, http://www.ngs.noaa.gov/PUBS_LIB/Illinois_harn.pdf but it doesn't really give me the warm fuzzy to buy a L1 only unit.  I'm used to the DOS command line of TEQC to convert to RINEX for uploads to OPUS.

Illinois is a bit light on CORS locations, but I note enough in the Marshall County area to make the following doable.

Using Ashtech's GNSS Solutions create a VRS (Virtual Reference Station) point near your L1 observation. The VRS is an imaginary L1/L2 observation close enough to your L1 observations to avoid the necessity of having L1/L2 receivers. You solve from this imaginary base to your L1 field point. I have used it and know it works. Solutions automatically gets the required CORS data. I would have loved to have had it years ago when I did quite a bit of positioning using 3 ProMark 2 receivers from downloaded CORS sites. Today I have L1/L2 receivers so after knowing it worked I had no further need to test.

If you want to locate surveys using L1 receivers it is best to have at least 3 so that you can mean out your network. In the distant past I regularly used the 3 nearest CORS in Ashtech Solutions to get 3 different field positions which I meaned. It is best to find 3 CORS that form a triangle around your project. Then holding my meaned position fixed I checked how close the L1 CORS positions was to record. 3 ProMark 2s can be had today for under $5,000 possibly under $3,000. 

Paul in PA

Paul thanks for the follow up.  Curious as to what is your collection time under this methodology?  I've seen some multi L1 bundles around the price point you mentioned.  In my private sector life, we had been able to get by with a single L1/L2 unit with a two hour occupation on two local project control points.  We always set three control points so the total station (TS) could occupy one while we had a GPS reciever camping on the other two during data collection (after backsighting one or the other) usually a spare Sokkia GSR2300 rover.  We used an assumed coordinate system on the first day for the TS, post processed the two points in OPUS and then adjusted to SPC for any return trips.

Seems like a toss up if we went with new equipment, a new single Sokkia Strata L1 is $2995 but I'd need multiple units whereas a new GRX1 L1/L2 Static is $6495.  The L1 route is certainly a new workflow to me, can you point me at some additional resources to read up on the VRS methodology?  Sounds like a possible consideration if I can find a deal on the used equipment route.  Right now I'm having to make a pitch to "upgrade" an 80s vintage digital theodolite and EDM to a used Sokkia Set 2110 for $2300.  GPS will a whole other hill to climb.

In the pway past if I happened to be in an area where a close COOP CORS had 15 second data, I would switch to 5 seconds for better commonality. Now that most COOP CORS can be downloaded through NGS I can usually get 5 or 10 second data from a 15 second CORS via ufcors interpolating the record file.
Knowing that I stay with 10 seconds. If I were planning shorter sessions I would increase the rate to 1 second, but in most cases I am seeking good elevations so my sessions are longer than minimum.

Paul in PA