The Dancer Project

GPS Dancer is a voluntary project of the International Association of Geodesy.

The next project milestone will be to install a core network of Dancer peers for all GNSS stations in the formal ITRF.

As a project, GPS Dancer is rather unique. It started as an initiative of the IAG Working group on "Comparison and combination of precise orbits based on different geodetic techniques", which existed from 2004 to 2010. This was probably the first time that some IAG component launched a real software development project, which is unusual because IAG Working Groups have no budget. They are merely professional networks of experts in a certain specialist field.

IAG Commissions, Sub-Commissions and Working Groups also have a limited lifetime. Every 6 years or so, the entire IAG is reorganised under a "sunset provision", for sensible reasons of innovation explained here. If some project or activity has not yet completed by the time of the organisational reform, there are two options: just stop with the project, or find another formal platform for it. The GPS Dancer project was going rather well, so obviously we went for option B. The main issues were to properly define the Intellectual Property Rights of the Dancer software, and to ensure long-term continuity of software maintenance and the on-line Dancer network solution, once it would have been deployed.

The GPS Dancer system is available under the Apache II license, but it is not (yet) a formal Apache project. A project does not have to become a formal Apache project in order to use the Apache license. It could just adopt take the license, even modify it to its own needs, and call it the Comanche license. However, the advantages of just using the existing Apache license is that many users will already be familiar with it. Official Apache projects apoint the "Apache Software Foundation" as the owner of their software. If only the software would be at discussion, the Dancer project could have done exactly the same thing. However, Dancer must also organize the ownership of the operational GPS Dancer network solutions. These are of course available to every Dancer peer in the network but may also be of interest to the scientific community, most notably to the IGS.

In particular, two aspects of the operational Dancer system must somehow remain under control of the IAG, or a closely related sister organisation:

  1. The start-up of the official Dancer network on-line should remain the privilige of a single entity. This avoids the appearance of dozens of separate Dancer systems, each using their own slightly modified models or processing approach, and each being unable to communicate with any of the other networks. By safe guarding the on-line network, we ensure that only one global reference frame solution is defined by Dancer, which was the whole point of making the system. Some person or organisation must be in charge of this.
  2. Updates of models and standards require a formal update of the software. The mechanism to do this automatically is already part of the Dancer software, but we cannot just give anybody in the world the capability of changing the on-line Dancer software. Again, some entity must be in charge of this.

During the development of the Dancer system, the system administrator was the only person who knew the password to start-up the on-line network. For the operational network, this would be a dangerous situation, because if he falls of a cliff or gets hit by a bus, the ability to upgrade the Dancer software would also be lost. The details of how to do these administrator tasks are therefore parked in a new non-profit organisation, called the Global Geodetic Grid Foundation, or GGGF. The GGGF (not the Apache Software Foundation) is the formal IPR holder of the Dancer software, and releases the software under the Apache II license because the latter is well-known, which makes life easy on the Foundation, and on the users. The GGGF is also the formal owner of the administrator rights (and passwords) for starting up the network, or releasing a software update.

Because users can get the Dancer software for free from the foundation (...in fact, from this website) nobody needs to pay for getting the system. However, a Dancer process is computationally demanding, and if you operate a few hundred GPS sites you will simply need a few hundred computers to join the Dancer network. A far more practical way of running your own Dancer processes, is to launch them in the cloud.

Because each Dancer peer is an independent process, starting and stopping Dancer processes becomes a tedious task: the same actions of login in a cloud computing account, uploading the system, and launching it must be repeated dozens, or hundreds of times. To make life easier on the users, a web-portal is currently being implemented that will do all these menial tasks on behalf of the operator. The user opens a single account in the web-portal, configures the data upload from his receiver(s) to this account, and the webportal takes care of launching the Dancer processes for all these receivers in commercial cloud computing capacity. After completion of each Dancer run, the outputs of all peer processes are availble for download in the same user account. This exposes one account to the user instead of a few hundred, and one interface to the Dancer system instead of one per peer process. Obviously, only the user has access to data and products, via password protection and via a non-disclosure agreement. The webportal disperses the Dancer peers evenly over different commercial cloud computing providers in Europe, the United States and Asia - the user could not care less where the processes are actually running. The costsof the commercial cloud computing capacity are passed on to the user, because the GGGF has no money of its own.

Unfortunately, the lawyers tell us that it is illegal for the GGGF to run such a web-portal: it is effectively a commercial undertaking, because it involves buying and selling goods or services (...the actual cloud computing capacity needed to run your Dancer peers). Hence, yet another organisation would be necessary that is run like a business, and is not financially affiliated with the GGGF directly. The provisional name of this organisation is Geodetic Cloud Computing Service (GCCS).

The GPS Dancer project does not want to see commercialisation of the Dancer system or its on-line operations. Even though this is made impossible by the creation of the GGGF foundation, the creation of the GCCS is still under consideration by the time of this writing (early 2013), and will be carefully discussed with all involved parties in IAG and IGS.

The various options of running your own Dancer process will then be as indicated in the Figure below. Any user can get the Dancer software from the foundation, and run it on his own hardware. This will typically be rather expensive, especially if you operate a few hundred sites.

The second option is to get the software from the Foundation, and launch it in commercial cloud computing capacity of your own choice. This is much cheaper and more practical than option A, but still requires interaction with and monitoring of each of your individual Dancer peers in the cloud. You probably need one or two operators for that, and some local server at your premises to automate all interactions between your Dancer processes and your receiver network.

The third option is to use the proposed GCCS service, which greatly simplified your own effort and avoids local cost. You still pay the same cloud computing cost as in option B.

As long as a Dancer user maintains the free choice to run Dancer in any way that bests suits his needs, the option of formally creating the service is in fact quite attractive to the GPS Dancer project. It means that we will qualify for various external government subventions and incubation schemes, which would immediately provide the funding for running an operational ITRF backbone network over several years. In cooperation with the receiver manufacturers, this might bridge the period between the initial Dancer operations, and the time that proper "smart receivers" become available. However, if anybody has a better idea, we remain open for alternatives.

 

Figure 1: proposed organisational structure for system maintenance and network operations, separating semi-commercial activities from the scientific objectives of the GGGF

 

 

Project details

Ultimate Browsers SupportThe GPS Dancer project started in 2007 as a voluntary project of a working group of the International Association of Geodesy.

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Square dance algorithm

Great Docs and SupportThe GPS Dancer system was named after its "square dance" exchange algorithm. Of course, it also wants to to make the GPS reference frame denser.

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Here, there be pirates

The Dancer on-line network became immune against internet connection problems by leaving the US marines, and becoming a pirate.

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