My state DOT (INDOT) recently upgraded to 4 constellation corrections for its CORS network. They offer several correction types, but we will use iMAX or VRS corrections for our rovers (BRx7 w/SurvPC).
There is lots of great info online on the ups and downs, possibilities, impacts, etc. of each correction type. We will be trying both for a while and see what really works best for us in the field with our equipment and software.
Do you guys have any input, experience or opinions on which correction type you prefer?
I have just got our Trimble units on a Leica network and am slowly testing the different message types and systems types. They all produce and have not figured out just which to use yet. VRS for Trimble gear is easy. I have tried the IMAX with Trimble receiver and a few other mounting points . I would cook a point or two somewhere easy access static wise to nail it down then just test the different configurations with BRX7 and message types at different parts of the day on and off to see which one’s values and Precisions etc seem doable.
I prefer the MAX/iMAX corrections over VRS. My main gripe about VRS is all of the 'virtual' CORS you end up with. iMAX gives you a vector from an actual 'master' CORS with atmospheric/ionospheric correction derived from the surrounding 'auxiliary' CORS. It makes it nice for any post survey review.
VRS give the vector and ionosphere corrections etc as well if they have it set up correctly and in the dc it’s set up.
I prefer the MAX/iMAX corrections over VRS. My main gripe about VRS is all of the ‘virtual’ CORS you end up with. iMAX gives you a vector from an actual ‘master’ CORS with atmospheric/ionospheric correction derived from the surrounding ‘auxiliary’ CORS. It makes it nice for any post survey review.
It is all virtual. The difference is whether you prefer Leica or Trimble. You could calculate a vector to any CORS you like.
I realize that both systems both systems use multiple CORS to best model the atmospheric, ionospheric and other corrections needed to extend the dependable length of the RTK vector. My point was more about from where that vector is begins. In the iMax/Max environment, the vector begins at the master CORS. If, for some reason, I choose to use something other than the transmitted realization it can be done by simply after the fact. Every time I have utilized a VRS system I have ended up with short vectors from multiple virtual CORS. While it might be possible to change the values, it seems a little more complicated. Another issue is reporting your results. While a VRS system will inherently have shorter base lines and thus less uncertainty based on its ppm, the majority of the error will be made up in the value of the virtual CORS. How is that reported?
I will say that my experience with VRS is limited, mostly for small scale mapping control on the magnitude of a county or forest. For these projects I have always ended up with a large number of virtual CORS, basically per observation. I'm not sure how many are created for a typical job site.
I'm not trying to which system is better, this is just my personal experience.
Near as I can tell (and with only limited experience), with a VRS the vector data from the PRS (the hardware CORS) to the rover is available to Trimble Access, but not to 3rd-party data collectors. I know this is true with Javad, and I've been told it pertains to Leica as well. They only get the virtual-base-to-rover vector, which is worthless for post-processing and adjustment.
I had planned to do a project in OPUS Projects using my Javad for the NRTK data, but the Javad was unable to extract the PRS vector data from the stream. I ended up buying a used R8-3 and renting a TSC7 to collect the data instead.
Thanks for the info Jim. That really seems match my experience with VRS and Leica hardware. Talk about proprietary.
