Archive for 2006

NAVITEC Workshop Report

Thursday, December 14th, 2006

I just attended the ESA sponsored NAVITEC Workshop which is a very welcome effort to bring together mainly european efforts in GNSS signal processing, applications and hardware.

The workshop was well attended and the atmosphere was cordial and welcoming. Many old faces on the European GNSS field take these opportunities to meet-and-greet each other, and the newcomers and students have a good chance to learn and to network.

The workshop had very interesting presentations on LEO (Low Earth Orbit) GNSS receivers, these are mounted on low flying scientific satellites (300 to 1200 Km). These receivers have been flying for the last few years but only recently has Europe had complete systems developed and in operation such as the GRAS receiver on Metop. These receivers can aid in the navigation operations of the satellite but are mainly used as scientific instruments to analyse the Earth’s atmosphere through occultation processing: Sounding the Atmosphere, Zandbergen & Dow

There was as expected a lot of work presented on multipath correction and mitigation techniques. As GNSS moves into more realistic consumer applications one cannot simply assume that the user will have a clear sky view. More than likely all upcoming “real” civil applications will have obstructed views and that leads to reflecting surfaces and thus to multipath. Some of the modern navigation codes are advertised as much better in terms of multipath attenuation, but some correction and mitigation will always be welcome.

Some other very interesting presentations included: the use of the GPStk library to build a receiver in a mini-computer, the simulated single frequency navigation solution of a LEO using a COTS receiver down to sub-meter accuracy, the implementation of L1/L2C receivers, EGNOS and Galileo Status presentation and EGNOS Signal in Space characterisation and applications.

The workshop was very well organised at ESTEC, as usual the facilities there are very welcoming and having an initial general session and two parallel sessions makes for a better workshop, too many parallel sessions are sometimes distracting and confusing for both speakers and listeners!. Having to access the ESTEC canteen at the same time as all the other ESTEC personnel probably inconvenienced the regulars more than was necessary since the workshop attendees could have been scheduled a bit later to avoid aglomerations, but all in all it was not a terrible problem.

I invite everyone to plan to attend the next Navitec in 2008, which I hear may be organised in Barcelona!

Happy Positioning!

Ignacio Romero

GNSS Antenna Phase Centre corrections

Thursday, November 30th, 2006

For precise GPS positioning and scientific applications it is important to recognize that the antenna phase centers do not represent fixed points with respect to the antenna reference marker (neither at the emitter end or at the receiver end).

The antenna phase center is the point where the receiver detects the signal and on the emitter side where the signal originates, this point actually moves as the geometry changes. The PCV (phase center variation) file has been used up to GPS wk1400 (Nov, 2006) to correct the GNSS measurements, this file specifies the corrections depending on elevation angle for most GNSS receiver antennas. The corrections are specified in relative terms by assuming that the first mass produced geodetic antenna (DORNE MARGOLIN) was giving the ground truth and all the other antennas where calibrated to that model antenna. The satellites were assumed not to have zenith variations and the Phase Center to Center Of Mass vectors where agreed to, according the GPS satellite block:

/* CLK ANT Z-OFFSET (M): II/IIA 1.023; IIR 0.000

Since GPS wk1400 the antenna calibrations have been changed. This effect has recently been calibrated for a very large number of antennas in an absolute sense using most available data from the last few years, and presented in a new international format called ANTEX (ATX). The new absolute calibration has as before L1 and L2 offsets (1st order effects) for all antenna types (receivers and now satellites!), it also contains elevation(zenith) dependent corrections for all antennas (2nd order effect), additionally there are azimuth effects (3rd order effect) for ground antennas since most of them do not have symmetrical correction maps:


Happy Positioning!

Ignacio Romero

What is GNSS about …

Wednesday, September 27th, 2006

For general information to the beginner I want to stress in this post the fundamentals.
I feel like they are often forgotten, and this is the most fundamental concept; ” It is all a matter of time!” With that phrase I mean to say that GNSS position is only possible because we measure the time ‘t’ that a signal generated in point X (the source) takes to travel to point Y (the receiver) and this time ‘t’ times the speed of light (300000 km/s ; 187500 mi/s) gives us a distance between points X and Y.

As long as we have 4 independent distances and we know the positions of all the sources we can calculate the 3D position of point Y. This is important; we need 4 distances because the emitter and receiver clocks are never synchronised properly by having 4 measurements we can solve the 3D + dT (receiver clock correction).

This is even more important; we must know the positions of the emitters and their clock corrections to a high degree of accuracy at the moment of the signal being emitted so that we can calculate the position of Y correctly. The GNSS constellations emitt each satellite’s positions and “clock bias” as part of the ‘Navigation Message’ encoded in the timing signal. It is also possible to use external sources for that information such as the IGS (IGS, etc).

In future blogs I will explain some of those fundamentals elements in more detail.

Happy Positioning!

Ignacio Romero

GNSS options

Friday, August 4th, 2006

When buying a new receiver for precise applications (where sub decimeter precision is needed) it makes sense to get a multi-constellation receiver.

A multi-constellation receiver takes the signals from the GPS and GLONASS satellite navigation constellations to calculate the receiver’s position more precisely and more robustly.

In environments where the open-sky visibility may be compromised the multi-constellation option greatly enhances the usability and precision.

Good luck and Happy positioning!

Ignacio Romero

Navigation and P-commerce

Monday, June 19th, 2006

Position and Navigation are the latest addition to the new economy, it is becoming necessary to be able to position every valuable item in the economy. This will be accomplished by GNSS services in the next decade.

An additional benefit will be the ability of certifying a position whenever it is needed. For example proving that one is within a certain region to access sensitive data or information.

It is also unquestionable to me that all the transport of sensitive or dangerous equipment, materials and residues needs to be properly tracked whether travelling by air, sea or land. Especially in areas as heavily populated as Europe it makes no sense to endanger the people and the livelyhood of thousands of people by uncontrolled dangerous shipments. In cases like the ship Erika (tanker that sank near France) and the Prestige (tanker that sank near Spain) the case has been proven that these ships need to report their certified position to central a “traffic control” center. The certified position would come from the combination of the Satellite Navigation Services (GPS, GLONASS, Galileo).


What is needed now is the agreement at governmental level and of the shipping companies that it is in everyone’s benefit to add this kind of equipment to ships to improve their services and everyone’s safety.

Happy Positioning!

Ignacio Romero

Canary Advanced Solutions starts!

Friday, May 5th, 2006

The core business of SAC is Satellite Navigation; GPS, GLONASS, Galileo. An expert recently commented that we are moving from the “information age” to the “position age”, all the same information will be available but we will be able to add value and context by including accurate certified position and time information. In critical and non-critical applications real-time position and time will become basic in a multid of services. We would like to be your partner in discovering new ways to use SatNav to add value and service, contact us with your ideas!

One thing that truly motivate us at SAC is the provision of off-site services using modern technologies. We have found that using good engineering and communications practices many organisations do not need the big overhead of having an entire development team in one place, they can be easily distributed and produce superior results. In the european context this may not be as fully exploited as it should be, if you want to implement such a system let us know, we can help!

Soluciones Avanzadas Canarias arranca!

Friday, May 5th, 2006

Lo que más nos motiva en Soluciones Avanzadas Canarias es nuestra area de trabajo: La Navegación por Satélite : GPS, GLONASS, Galileo. La navegación por satélite presenta una serie de oportunidades fantásticas en el futuro próximo. Estamos pasando de la era de la “información” a la era de la “posición”. Los mismos paradigmas seguirán existiendo pero cada vez más y más añadiremos contexto y valor a la información con la posición y el tiempo, en “tiempo real”. La posibilidad de certificar una posición y un tiempo añadirá servicios en aplicaciones tanto críticas como no críticas en los próximos años, de una forma todavia ¡inimaginable!

Otra cosa que nos motiva mucho en Soluciones Avanzadas Canarias es la provisión de servicios de ingeniería de manera remota; ¡el llamado tele-trabajo es algo que funciona! En los últimos años hemos acumulado mucha experiencia y hemos encontrado que usando buenas prácticas de comunicación y de ingenieria no hace falta tener a todos los desarrolladores de un sistema complejo en el mismo lugar. Desde el 2004 venimos demostrando que grandes organizaciones pueden ahorrarse tiempo, dinero y problemas y, a su vez, obtener resultados superiores, si se aplican bien las lecciones aprendidas y se distribuyen los equipos de desarrollo sobre diferentes áreas geográficas. Soluciones Avanzadas Canarias puede ayudar a cualquier empresa a implementar estas lecciones: Contáctenos si le interesa que estudiemos juntos su problema particular.

Les invito a leer los blogs donde desarrollamos las ideas de la empresa y del mundo GNSS, y también les invito a contactarnos con cualquier duda o idea que le surja.

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