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Calgary, AB, Canada | Kelly,
Thanks for the question. I have been involved with CDGPS in Canada, for several years, as a retailer and I now work for a major manufacturer of agricultural GPS systems.
CDGPS was concieved over a decade ago to be used in northern Canadian conditions, where existing SBAS corrections were not available. When you look at a map of Canada, 90% or so of the population lives within 200 miles of the USA border. That leaves a whole lot of territory! The Canadian government owns most of this land, as thus needed to accurately survey the land. The existing GPS corrections simply did not function well at northern latitudes. So over a decade ago, the government started a project to have a survey grade correction available free of charge that would work in all of Canada. The signal was designed for ground use vs. avaition for WAAS, and the signal was designed to penetrate folige better than WAAS. In some of the areas that I work, before the upgrading of WAAS (moving PRN122, and adding 135, 138), some of the WAAS sat elevations were less than 5 degrees, which made it very difficult to use.
The CDGPS organization, which consists of NRCan (Natural Resources Canada, a Government department), who actual produce the corrections (called GPS-C) and CDGPS (a Parnership between the Federal Gov., the 10 provinces, and 3 territories), which looks after the distribution. The Canadian government has committed to keeping CDGPS a free correction. You could say that CDGPS is owned and controlled by the Canadian government. While this is true, the CDGPS management actively solicits input from GPS manufacturers, industry, service providers, etc. to help make the signal better and more widely used. I recently attended one of these meetings, and the future of CDGPS looks bright indeed.
Originally, the CDGPS coverage map was for Canada only. (http://www.cdgps.com/e/cov.htm), As of May 6 this year, the coverage area with valid corrections extends into the Gulf of Mexico, from Atlantic to Pacific, including the area in the link above. So CDGPS now has a much larger useable footprint than WAAS. You need a CDGPS capable receiver to access the correction. Right now, only NovAtel (novatel.ca) has included CDGPS capability in some of their dual frequency receivers. For agriculture, only the Raven 410 and Phoenix 300 are CDGPS capable, but I know other manufacturers are considering it.
The key difference in CDGPS vs WAAS is the correction sentence itself. WAAS is based on a precision of 0.125M message structure while the high accuracy messages such as MRTCA (CDGPS) have a precision capability of 0.004M. These high accuracy messages are required if you are to try and get into the 10cm, 2 Sigma range (Omnistar XP/HP) by using a phase correction. While CDGPS does not presently offer the phase correction, the capability is already built into the message structure (read between the lines!)
In two years of testing, at my latitude, 53.50 N, CDGPS showed a 10-15% increase in static accuracy vs WAAS. That may not hold true at more southern latitudes where WAAS works better. I know that NovAtel dual-frequency receivers will be capable of sub 50cm static accuracies using CDGPS by later this year. This is on a free correction. Many farmers in Western Canada are starting to switch from WAAS to CDGPS, not only for the slightly improved accuracy, but for the ability to switch between correction signals if one or the other gets a little "flakey).
IMHO, CDGPS has a very bright future, not only for agriculture, but for many other industries. In some ways, its history is similar to WAAS. WAAS was not created for agriculture, but there is no denying that it has proved very benificial for agriclture. CDGPS is the same, while it was created for northern survey work, it too has found a useful place in agriculture and will become more widely used in the years ahead.
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Question for Doug S-CDGPS?
