Archive for October, 2010

Regional PPP

October 25th, 2010 by Ricardo Píriz

Precise Point Positioning (PPP) is normally understood as a global positioning service, since precise satellite orbit and clock products used as input in PPP are best calculated using a network of GNSS reference stations distributed worldwide.

However orbit and clock corrections for PPP can also be provided over a world region in a similar way to WAAS or EGNOS corrections. It is even possible to provide a national PPP service over a single country, using national GNSS stations exclusively.

Satellite orbits and clocks calculated using regional stations do not have of course a high overall accuracy, but they do have a higher accuracy over the service area and, most importantly, orbit and clock errors largely cancel out over the service area. For a static or kinematic PPP user located inside the region, positioning accuracy using global or regional products is very similar.

In magicGNSS version 3.1 it is possible to evaluate the performance of regional PPP in a very simple way. Just process an ODTS scenario to calculate orbits and clocks covering the time period of your interest. On the Stations tab, select stations over your region only. Click on the station icons to select/deselect, you can use core stations and/or your own stations.

In regional ODTS it is better to deselect “Refine Station Coordinates” in Settings. Core stations have already precise coordinates, and for your own stations you are supposed to have processed them beforehand in PPP using the “Update My Station Coordinates” option. Try also to use a longer ODTS scenario duration (3 to 4 days), in order to maximize satellite visibility. It is also important to select a good reference clock in ODTS. The reference clock time should be close enough to UTC (or GPS Time), with an offset of the order of the microsecond or less. You can see the offset of a station clock by processing it in PPP.

When ODTS processing is ready, create a new PPP scenario for that period, and select Products from the ODTS scenario you just processed, instead of the global ones (Operational):

You can use COMP to compare static or kinematic PPP solutions using global and regional products.

Kinematic positioning now available

October 6th, 2010 by Ricardo Píriz

It is now possible to process kinematic data in the latest magicGNSS version (3.0). Precise Point Positioning (PPP) supports now both static and kinematic modes, including GPS-only, GPS+GLONASS, and GLONASS-only data.

Flight over Louisiana (from the Kinematic GPS Challenge)

You can download this KML file generated by our kinematic PPP, and corresponding to one of the flights from the Kinematic GPS Challenge. In Google Earth, use Shift-s and scroll with the mouse to see the flight in perspective.

Combined GPS+GLONASS products used by PPP (satellite orbits and clocks) are internally generated with a 30-min latency. Note that our internal clocks have a 5-min rate. Final IGS products provide clocks at a 30-sec rate (GPS only), and they are used by our PPP when they become available (2-week latency).