Introduction

1. Distributed processing systemsfor large geodetic solutionsIAG WG 1.1.1“Comparison and combination of precise orbits derived from different space geodetic techniques”Henno Boomkamp REFAG2010 Paris

2. Introduction • Objectives of IAG WG 1.1.1 • Study systematic errors between orbits based on different data • Improve models and solution strategies • Develop the means to allow the above • Key solution mechanism: simultaneous analysis • simultaneous (re-)processing of geodetic datasets is either free of biases, or allows estimation & analysis of inter-system biases • Concrete targets • Analysis of all GPS / GNSS data in a single solution Dancer • Analysis of all geodetic data in a single solutionDigger REFAG2010 Paris

3. Dancer • - data types: GNSS & VLBI • - short arc (48 hrs) • short latency (30 min) • key technology: JXTA POD module ITRF Large scale, direct access ITRF • Dart (Dancer-RTK) • data types: GNSS only • very short arc (RT) • zero latency • key technology: BURST • Digger (… reprocessing) • data types: all • long arc (years) • long latency (1 week) • key technology: BOINC Real-time access to accurate ITRF Consistency among techniques Three WG projects Effort: Dancer 90 % Digger 9 % Dart 1 % REFAG2010 Paris

4. 20,000 permanent GPS receivers 5,000 public 400 ITRF The trouble with GPS • Limited processing capacity of AC • Current IGS approach would require hundreds of Analysis Centres … • Most data not available at short latency • Reduces statistical quality ITRF • Reduces relevance of ITRF • If we want to run a conventional batch LSQ solution for all receivers • Distribution over many computers is inevitable • Geographical separation of the computer cluster is inevitable REFAG2010 Paris

5. 10 GPS sites = 10 PC = 10 AC REFAG2010 Paris

6. Dancer overview Dancer brings the analysis to the data rather than vice versa • LSQ solution implemented as a peer-to-peer process on the internet • Based on existing JXTA P2P software (SUN Microsystems) Natural separation of analysis is by receiver, not by AC • Geographical distribution of data is at the level of receivers • Solution becomes scalable in the number of stations • 99% of estimated parameters can be pre-eliminated at receiver level … the required computers are readily available! • Every permanent receiver is connected to a local or remote computer • Most of these computers do not do anything apart from RINEX ftp • Processing capacity is perfectly collocated with the data owners REFAG2010 Paris

7. global (orbits, sat clocks, pole) local j = 1 … N Separation of LSQ in tasks per receiver (1) Local parameters are pre-eliminated at the receiver: • With 10,000 receivers: • Total solution • 30 million parameters • 170 million observations • After pre-elimination • 90,000 global parameters • Single process • 15,000 non-zero eq. REFAG2010 Paris

8. Separation of LSQ in tasks per receiver (2) Global normal equation represents the average equation of all receivers Dancer averages diagonal Dbefore solution, and the vector afterwards Same solution , thanks to distributive property of multiplication with REFAG2010 Paris

9. Averaging N vectors without a central serversquare dance algorithm • N/2 pairs can be formed by toggling one bit of each number 1...N 011010110  111010110 • Pair-wise exchange of vectors: both computers find the same sum x11010110 first bit has now become irrelevant… • New exchange pairs are formed by toggling the second bit 011010110  101010110 xx1010110 first two bits are now irrelevant; etc… • Some additional operations are necessary: • folding nodes are introduced to make N an exact power of two • N splits into 50% core nodes and 50% spare nodes for contingencies After log2Nexchange cycles, all N computers have the same vector REFAG2010 Paris

10. MB arc length / epoch rate N core node data volume (1-way) REFAG2010 Paris

11. Dancer project status Sched  beta REFAG2010 Paris

12. Summary • Rigorous LSQ solutions for all GPS receivers are possible • workload can be distributed over (some) existing hardware • Dancer has no data centres,analysis centres,combination centres,product centres, central bureau… • anonymous participation avoids political issues of data access • differences regional vs. global reference frames disappear • GNSS receivers become smart receivers • Dancer process can be embedded on future receiver hardware • Smart receiver generates products, not (just) observations • Other distributed processesto follow • DIGGER simultaneos reprocessing of all geodetic techniques • DART RTK layer on top of Dancer for global access REFAG2010 Paris

13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . www.GPSdancer.com • for • further information • more details on solution mathematics • download latest version of the software • check project status • e-mail contacts and web links Dancer screenshot REFAG2010 Paris