As explained in the previous entry of this blog, the ODTS algorithm inside magicGNSS is able to calculate precise station coordinates. Another technique that is becoming increasingly propular to calculate receiver coordinates is Precise-Point-Positioning (PPP).

The main difference between ODTS and PPP is that ODTS is a multi-station global solution that calculates also satellite orbits and clocks, and PPP is a single-station technique where satellite orbits and clocks are solved beforehand using an independent software (or are fixed to IGS solutions). ODTS is based on a batch least-squares algorithm whereas PPP is normally based on a sequential filter that solves for the user reciever coordinates, clock, tropo, and phase ambiguities.

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One of the available scenario settings is the “Refine Station Coordinates” check box. When this is checked, magicGNSS will estimate the station coordinates, yet keeping a constraint to their initial value, as provided by ITRF (or the IGS). This refinement can compensate for some inaccuracies, such as some mismodelling of the Earth motion, thus helping to achieve better performances.

On the other hand, when the observability is not good enough (e.g. when the number of stations/data is insufficient or their distribution is poor) the estimation of the coordinates may be correlated with other parameters and lead to a degradation of performances! So, should one check the box or not?

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As the magicGNSS blog gets more entries it obviously becomes increasingly difficult to find some specific information on it. But do not worry, that is why the Search window is there at the top right. Just type what you are looking for (e.g., “presentation” or “paper”) and click on Search. Enjoy!

What is the most exciting way to use magicGNSS? Actually, the easiest one! Inside your magicGNSS account, just click on New to define a new scenario (scenario Name and Start and End dates are provided by default), then click on Save to create the new scenario, and then click on Run to process the data and generate results.

In fact the application selects by default yesterday as Start Date and today as End Date. In this way you get the most recent ODTS estimations possible, for example to monitor the latest behaviour of all GPS satellite clocks, with a latency of just a couple of hours.

Start and End dates are relative to GPS Time, not to the local time of your town! Currently GPS Time is ahead of UTC by just 14 seconds, therefore UTC (or its equivalent Greenwich Mean Time) is a good approximation to GPS Time.

One of the objectives of magicGNSS is to make GNSS algorithms easy to use. No matter how complex these algorithms actually are, settings can be reduced to a few key parameters. Default values for the other algorithm configuration options are provided by the application; they have been optimized to provide robustness and performances in most cases.

We have prepared a video tour that shows you how easy is to create and run an ODTS scenario with magicGNSS Beta. Don’t miss it!

magicGNSS Video Tour

Note: You will need QuickTime to watch the video.