The GPS Toolkit
The GPS position solution can be improved by using a better satellite ephemeris. The US National Geospatial-Intelligence Agency (NGA) generates and makes publicly available a number of precise ephemerides, which are more accurate satellite orbits. Satellite orbits described by the broadcast navigation message have an error on the order of meters, and the precise ephemeris has decimeter accuracy. The International GPS Service (IGS) is a global civil cooperative effort that also provides free precise ephemeris products. Global networks of tracking stations produce the observations that make generation of the precise ephemerides possible.
GPS observation data from many tracking stations are available freely on the Internet. Many such stations contribute their data to the IGS. In addition, many networks of stations also post their data to the Internet, such as the Australian Regional GPS Network (ARGN) and global cooperatives including NASA's Crust Dynamics Data Information System (CDIS).
Typically, GPS observations are recorded in a standardized format developed by and for researchers. Fundamental to this format is the idea that the data should be independent of the type of receiver that collected it. For this reason, the format is called receiver independent exchange, or RINEX. Another format associated with GPS is SP-3, which records the precise ephemeris. The GPSTk supports both RINEX and SP-3 formats.
GPS receivers have become less expensive and more capable over the years, in particular handheld and mobile GPS receivers. The receivers have many features in common. All of the receivers output a position solution every few seconds. All receivers store a list of positions, called waypoints. Many can display maps that can be uploaded. Many can communicate with a PC or handheld to store information or provide position estimates to plotting software.
Typically, communication with a PC and other system follows a standard provided by the National Marine Electronics Association, called NMEA-0183. NMEA-0183 defines an ASCII-based format for communication of position solutions, waypoints and a variety of receiver diagnostics. Here is an example of a line of NMEA data, or sentence:
The data here is a latitude, longitude fix at 51° 33.81 min North, 0° 42.25 min West. The last part is a checksum.
As a public standard, the NMEA-0183 format has given the user of GPS freedom of choice. NMEA-0183 is the format most typically used by open-source applications that use receiver-generated positions.
Closed standards also are common. SiRF is a proprietary protocol licensed to receiver manufacturers. Many receiver manufacturers implement their own binary protocols. Although some of these protocols have been opened to the public, some have been reverse engineered. GPSBabel is an open-source project to communicate with consumer-grade receivers. The Sharc Project is a similar project to provide communication with survey-grade receivers.
A number of interesting open-source applications are available that utilize consumer-grade receivers. With one, you can use open-source applications to navigate in your car. The GPS Drive Project helps you do that, using a graphical map. GPS Drive also can be linked to the Festival application to get driving directions in the form of speech output. Internet sites such as WiGLE.net have lists of the geographic coordinates of open wireless LANs; you can use your GPS unit to find these.
Traditionally, DGPS is accomplished with two or more receivers that communicate position information with radio waves. You can do DGPS over IP now, using open-source applications. The open-source project called gpsd essentially broadcasts NMEA-0183 sentences over TCP/IP. The gps3d Project, which allows you to visualize your position and the configuration of GPS in 3-D, also can utilize a gps3d server.
All of these applications are based on standard positioning. To move your positioning capability to the next level, you have to work directly with the observations made by the receiver. Only a few open-source or freely available programs exist that give the user this freedom. OpenSourceGPS is a project to create a GPS receiver based on the Zarlink chipset. teqc from UNAVCO performs quality assurance and processes raw data from receivers to generate RINEX, but it is closed source. In contrast, the purpose of the GPSTk is to give the user the ability to manipulate not only GPS observations but also to improve the processing algorithms.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide