VRS Question

I think it depends on how it was set up. The Trimble one Seiler set up for Missouri had to be good for ten miles outside the state. A lot of the Illinois side of St. Louis metro area falls within this zone, and I've heard it's all still good. Same at Hannibal.

It probably depends on what each States specs were when they set it up.

Thanks Marc

I looked at the station list for MODOT's network and it looks like they include stations in the neighboring states to get the 10 mile coverage.

I'm working near the Nebraska/Iowa border and I'm centered about 25km from the nearest IADOT and NE Seiler stations. Unfortunately the Nebraska Seiler network and the IADOT Leica network don't overlap stations...I'm sorta stuck in no mans land trying to figure which network would be the best to run off of.

It has been our experience that you can work off either one as long as you tell the data collector which state to show coordinates for. We have recorded 30 miles outside state lines.

VRS Question, Since All Projects Require Hard Control Points

Have enough control to encompass your site, then observe all control points using the State "B" network, then repeat using the State "A" network followed by your project itself. At the end of the day, reoccupy all control using both networks. Convert, compare with your field traverse and adjust if necessary back in the office.

If you do not do field traverse you will never know how good or bad your GPS is, no matter how many people you ask.

Paul in PA

VRS Question, Since All Projects Require Hard Control Points

Paul,

Thanks for the survey 101 lesson. Not sure how your method would determine if you were getting a true network solution or single base. Obviously I will calibrate to local control no matter which network I use.

A True Network Solution Requires You Be Within The Network

Since you are not within either network by definition you do not have a network solution. To be within a network requires 3 CORS sites . Because you are outside of either network your position most likely is from less than 3 CORS.

Being outside a network however may yield a solution from 2 CORS or sometimes a single CORS. If you can get a 2 CORS solution from both networks or even a 2 and 1 solution you may find yourself within a CORS framework and the solution may approach the precision of a network. My suggestion allows you to confirm your 2 or 1 CORS solutions are within your acceptable precision range.

Theoretically a single GPS receiver could output to multiple devices or a multi use computer program each comparing to a single CORS data and thus you could create your own network.

The simplest solution to your problem has been around for decades, it is caked RTK and requires you have a base station receiver. VRS allows one to survey within a network by creating that receiver in the form of a Virtual Reference Station.

In today's market a second GPS receiver is most likely cheaper than the computer hardware/software costs to replicate that receiver.

Paul in PA

VRS Question, Being Within A Network

Seems like there are more than 1 Surveying 101 questions to answer.

Being within a network allows the VRS program to interpolate corrections based on at least 3 receivers.

Being outside a network requires the VRS program to extrapolate corrections based on available 3 receivers, possibly 2 or 1. Precision degrades much more rapidly outside the network and may also vary with the software algorithms used.

Using RTK the software assumes you are so close that the corrections are the same as at the base.

The software used for OPUS-RS (RSGPS) is a post processed network solution using up to 9 reference stations. Even with 9 stations it is possible to be outside the reference station box and OPUS-RS does provide some close extrapolated solutions.

Because OPUS-RS picks the nearest reference stations and there are so many around here I sometimes get an "outside the polygon" abort or solution. I can then force 1 or 2 CORS choices farther away and hence become inside the polygon. I may or may not see a coordinate change with an outside to inside solution.

Hopefully we do not need any Geometry 101 answers.

Paul in PA

Have you checked into the Leica SmartNet coverage for Nebraska? Here is the coverage map: http://smartnet.leica-geosystems.us/coverage_network.cfm

Beavers area of work probably is just outside the SmartNet also.

However three outside the network solutions should be very helpful.

Paul in PA