DGPS Beacons used by Trimble being discontinued?

I didn't see that location in the list of stations in the article.

DGPS is/was used by many. It is being discontinued to save the government money. Therefore you get to pay for a private differential service. The alternative is to consider ranging from SBAS (WAAS) satellites as per the Ashtech BLADE Technology. Trimble now owns Ashtech and BLADE ranging is available in certain Trimble products.

Paul in PA

With my RTK rover and WAAS correction I get sub-meter accuracy (around 50cm). That's about what I was getting with the Pathfinder Pro XRS and beacon DGPS. Guess I'll start using the rover with WAAS instead of the Pathfinder when sub-meter is good enough. In Missouri and Minnesota I get cm accuracy with my rover using the MoDOT and MnDOT Real Time Network (RTN). Be nice if all DOT's offered that service.

I think WAAS is a very useful (free) service for sub meter accuracy.?ÿ

But, I wonder how many users of WAAS are aware that it uses ITRF and NOT NAD83(2011). I have heard people say it is not accurate, but I believe they are comparing it against NAD83(2011) coordinates.?ÿ

Also interesting is the fact that the WAAS CORS located at the Mexico City Airport (MMX1) is sinking (the whole area is subsiding). The current published elevation is about 8 cm too high.?ÿftp://www.ngs.noaa.gov/cors/Plots/mmx1_08.short.png

I think WAAS is a very useful (free) service for sub meter accuracy.?ÿ

But, I wonder how many users of WAAS are aware that it uses ITRF and NOT NAD83(2011). I have heard people say it is not accurate, but I believe they are comparing it against NAD83(2011) coordinates.?ÿ

Also interesting is the fact that the WAAS CORS located at the Mexico City Airport (MMX1) is sinking (the whole area is subsiding). The current published elevation is about 9 cm too high.?ÿMMX1

In Carlson SurvCE there is an option box Convert WGS84 to NAD83. I noticed that when using my RTK rover autonomously and getting WAAS correction, if I compare the rover reading against a datum recorded in NAD83 and the box is unchecked the position is off about 1.5 meters, when it is checked it is off about 0.5 meters.

DGPS from WAAS has been available in all Trimble receivers going back at least as far as the 5700 and 5800, which were the first ones I used; it has nothing whatsoever to do with the acquisition of Ashtech and their buzzword technobabble.

And yes, most Trimble users in the US just use the straight up NAD83 coordinate system when surveying in NAD83 coordinates; there's a coordinate system in Access and TBC called ITRF to NAD83 that should be used with WAAS, which is as John stated in ITRF coordinates. You'll see the same meter level improvement that bisenberger saw in Carlson.

Most people I spoke with over the years felt that WAAS was less accurate than the DGPS Nav Beacons because they were unaware of the ITRF - NAD83 issue, and it wasn't until fairly recently (4 - 5 years) that Trimble added the coordinate system containing the transformation. WAAS is in fact much more stable and accurate than the RTCM Type 9 corrections delivered by the Nav Beacons.

Lee,

I am talking about ranging from the WAAS satellite, which is different from the WAAS correction. Since the Ashtech ProMark 3 L1 and the Z-Max L1/L2 the Blade Technology allowed the receiver to calculate a ranging distance to the any SBAS/WAAS satellite using the L1 SBAS/WAAS broadcast signal. This is similar to the C1/P1 or C2/P2 values deciphered from the L1/L2 satellite frequencies. Since the SBAS satellites are not changing positions as fast as the GPS it allows the receiver to have a reliable position estimate much faster that using the GPS alone. The US plans to add an L5 correction to be broadcast from WAAS give two very reliable distance to start a positioning calculation, very important for aviation usage.

Depending on the internal board not all Spectre Precision or new Trimble units have the capability. I believe some Leica and others also now have the capability.

Paul in PA