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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