Archive for July, 2009

GPS antennas and positioning

July 24th, 2009 by Ricardo Píriz

In GPS antennas, there are three important reference points that have to be considered, as shown in the following picture (borrowed from NRCan):


The Antenna Phase Center (APC) is the virtual electronic point that actually tracks the GPS signals. In principle, coordinates from any GPS receiver or station refer to this point.

However, for geodetic applications, since the antenna might be replaced by another model at some time, it is important to consider a physical point attached to the ground. This is called the Marker. (more…)

The Precise Point Positioning Software Centre

July 7th, 2009 by Ricardo Píriz

Our email-based PPP service is now part of the The Precise Point Positioning Software Centre (PPPSC). Four online PPP services are now included in the PPPSC. You can download an example of report with the results from the four PPP services currently included in the PPPSC. Here is another example.

Virtual PPP by email

July 1st, 2009 by Ricardo Píriz

No RINEX files at hand? Don’t remember where to download them from, or just too busy to do it? No worries: for IGS stations, you can now do virtual Precise Point Positioning by email (see our previous entry on PPP by email). With virtual PPP there is no need to attach RINEX files to your email, you just have to describe in the message body the station data you are interested in.

Just send an email to with the Subject Virtual and type one or two virtual RINEX filenames in the body of the message, with the following syntax:

rinex: ssssyyddd

where ssss is the station name, yy is the two-digit year, and ddd the day of year. For example:

Subject: Virtual

rinex: kokb08001
rinex: kokb09170

If you submit two RINEX files and they belong to the same station (as in the previous example), you will also get the comparison of the two PPP results (difference of coordinates).