Tuesday, December 27, 2005


A- Z of How GPS works

Our ancestors had to go to pretty extreme measures to keep from getting lost. They erected monumental landmarks, laboriously drafted detailed maps and learned to read the stars in the night sky.

Things are much, much easier today. For less than $100, you can get a pocket-sized gadget that will tell you exactly where you are on Earth at any moment. As long as you have a GPS receiver and a clear view of the sky, you'll never be lost again.

In this article, we'll find out how these handy guides pull off this amazing trick. As we'll see, the Global Positioning System is vast, expensive and involves a lot of technical ingenuity, but the fundamental concepts at work are quite simple and intuitive.

Trilateration Basics

When people talk about "a GPS," they usually mean a GPS receiver. The Global Positioning System (GPS) is actually a constellation of 27 Earth-orbiting satellites (24 in operation and three extras in case one fails). The U.S. military developed and implemented this satellite network as a military navigation system, but soon opened it up to everybody else.

Photo courtesy NASA

NAVSTAR GPS satellite

Each of these 3,000- to 4,000-pound solar-powered satellites circles the globe at about 12,000 miles (19,300 km), making two complete rotations every day. The orbits are arranged so that at any time, anywhere on Earth, there are at least four satellites "visible" in the sky.

Photo courtesy U.S. Department of Defense

Artist's concept of the GPS satellite constellation

A GPS receiver's job is to locate four or more of these satellites, figure out the distance to each, and use this information to deduce its own location. This operation is based on a simple mathematical principle called trilateration. Trilateration in three-dimensional space can be a little tricky, so we'll start with an explanation of simple two-dimensional trilateration.

2-D Trilateration

Imagine you are somewhere in the United States and you are TOTALLY lost -- for whatever reason, you have absolutely no clue where you are. You find a friendly local and ask, "Where am I?" He says, "You are 625 miles from Boise, Idaho."

This is a nice, hard fact, but it is not particularly useful by itself. You could be anywhere on a circle around Boise that has a radius of 625 miles, like this:

GPS Trilation

You ask somebody else where you are, and she says, "You are 690 miles from Minneapolis, Minnesota." Now you're getting somewhere. If you combine this information with the Boise information, you have two circles that intersect. You now know that you must be at one of these two intersection points, if you are 625 miles from Boise and 690 miles from Minneapolis.

If a third person tells you that you are 615 miles from Tucson, Arizona, you can eliminate one of the possibilities, because the third circle will only intersect with one of these points. You now know exactly where you are -- Denver, Colorado.

This same concept works in three-dimensional space, as well, but you're dealing with spheres instead of circles. In the next section, we'll look at this type of trilateration.

3-D Trilateration

Fundamentally, three-dimensional trilateration isn't much different from two-dimensional trilateration, but it's a little trickier to visualize. Imagine the radii from the examples in the last section going off in all directions. So instead of a series of circles, you get a series of spheres.

If you know you are 10 miles from satellite A in the sky, you could be anywhere on the surface of a huge, imaginary sphere with a 10-mile radius. If you also know you are 15 miles from satellite B, you can overlap the first sphere with another, larger sphere. The spheres intersect in a perfect circle. If you know the distance to a third satellite, you get a third sphere, which intersects with this circle at two points.

The Earth itself can act as a fourth sphere -- only one of the two possible points will actually be on the surface of the planet, so you can eliminate the one in space. Receivers generally look to four or more satellites, however, to improve accuracy and provide precise altitude information.

In order to make this simple calculation, then, the GPS receiver has to know two things:

  • The location of at least three satellites above you
  • The distance between you and each of those satellites

The GPS receiver figures both of these things out by analyzing high-frequency, low-power radio signals from the GPS satellites. Better units have multiple receivers, so they can pick up signals from several satellites simultaneously.

Radio waves are electromagnetic energy, which means they travel at the speed of light (about 186,000 miles per second, 300,000 km per second in a vacuum). The receiver can figure out how far the signal has traveled by timing how long it took the signal to arrive. In the next section, we'll see how the receiver and satellite work together to make this measurement.

Measuring Distance

In the last section, we saw that a GPS receiver calculates the distance to GPS satellites by timing a signal's journey from satellite to receiver. As it turns out, this is a fairly elaborate process.

At a particular time (let's say midnight), the satellite begins transmitting a long, digital pattern called a pseudo-random code. The receiver begins running the same digital pattern also exactly at midnight. When the satellite's signal reaches the receiver, its transmission of the pattern will lag a bit behind the receiver's playing of the pattern.

Photo courtesy U.S. Army

A GPS satellite

The length of the delay is equal to the signal's travel time. The receiver multiplies this time by the speed of light to determine how far the signal traveled. Assuming the signal traveled in a straight line, this is the distance from receiver to satellite.

In order to make this measurement, the receiver and satellite both need clocks that can be synchronized down to the nanosecond. To make a satellite positioning system using only synchronized clocks, you would need to have atomic clocks not only on all the satellites, but also in the receiver itself. But atomic clocks cost somewhere between $50,000 and $100,000, which makes them a just a bit too expensive for everyday consumer use.

The Global Positioning System has a clever, effective solution to this problem. Every satellite contains an expensive atomic clock, but the receiver itself uses an ordinary quartz clock, which it constantly resets. In a nutshell, the receiver looks at incoming signals from four or more satellites and gauges its own inaccuracy. In other words, there is only one value for the "current time" that the receiver can use. The correct time value will cause all of the signals that the receiver is receiving to align at a single point in space. That time value is the time value held by the atomic clocks in all of the satellites. So the receiver sets its clock to that time value, and it then has the same time value that all the atomic clocks in all of the satellites have. The GPS receiiver gets atomic clock accuracy "for free".

Using the Data

In the last couple of sections, we saw that the most essential function of a GPS receiver is to pick up the transmissions of at least four satellites and combine the information in those transmissions with information in an electronic almanac, all in order to figure out the receiver's position on Earth.

Once the receiver makes this calculation, it can tell you the latitude, longitude and altitude (or some similar measurement) of its current position. To make the navigation more user-friendly, most receivers plug this raw data into map files stored in memory.

Photo courtesy Garmin

The StreetPilot II, a GPS receiver with built-in maps for drivers

You can use maps stored in the receiver's memory, connect the receiver to a computer that can hold more detailed maps in its memory, or simply buy a detailed map of your area and find your way using the receiver's latitude and longitude readouts. Some receivers let you download detailed maps into memory or supply detailed maps with plug-in map cartridges.

A standard GPS receiver will not only place you on a map at any particular location, but will also trace your path across a map as you move. If you leave your receiver on, it can stay in constant communication with GPS satellites to see how your location is changing. With this information and its built-in clock, the receiver can give you several pieces of valuable information:

Source: www.howstuffworks.com

Friday, December 09, 2005


Love your mobile? Blame your personality

Teenager on the phone
Young people who can't live without their mobiles are likely to be extroverts or have low self-esteem, researchers say (Image: iStockphoto)

People who chat on their mobile phones in the movies or who have crippling phone bills tend to have particular personality types, say Australian researchers.

Psychology lecturer Dr James Phillips and his team from Melbourne's Monash University say people who are more likely to get into trouble with their dangerous or disruptive mobile phone use are young, extroverts or people with low self-esteem.

Their study, published in the current issue of the journal CyberPsychology & Behavior, surveyed 195 people over 18 about how they used their mobile phones.

Among the questions the researchers asked were about the size of their phone bills, reasons for calls, and aches and pains linked to phone use, such as 'SMS thumb' brought on by lots of text messaging.

The researchers also asked if family and friends complained about their phone use; if they were late to appointments because they were on the phone; or if they became annoyed when someone asked them to switch off their phone.

The researchers did not ask about using the phone while driving as study participants may have lied to avoid incriminating themselves, which would have affected the results, says Phillips.

Participants also undertook psychological testing that Phillips says shows a clear correlation between personality type and problem phone use.

"These people don't appear to value what they are doing at a particular time," says Phillips.

"They may have spent $100 on a Paul McCartney ticket but even that isn't enough to get them to switch the phone off."

Different reasons for a huge phone bill

Phillips says people with different personality types use their phones for different reasons.

"Those with poor self-esteem are more likely to seek reassurance using their phones or they are unhappy and using their phones to reach out to others," he says.

"While the extroverts tend to be using them more to make social arrangements with a large network of friends."

Phillips says the results would help authorities develop advertising campaigns to target problem users to dangers like using a phone while driving, in hospitals and at petrol bowsers.

"If we can predict who is more likely to have problem and why then we can target them in advertising," says Phillips.

He said problem mobile phone use could be fixed as it was similar to a "very strong bad habit or bad priority".
By Catrina Purcell
ABC Science Online

Thursday, December 08, 2005


Hands-free mobile no safer when driving

Agence France-presse

Holding a mobile phone while driving more than quadruples the risk of an accident, and using a hands-free phone kit is almost as dangerous, according to an Australian study.

Researchers interviewed more than 450 drivers in Western Australia who owned or used mobile phones and who had been involved in car crashes serious enough to warrant hospital treatment.

Most of the drivers also gave their permission to get records of the phone use from their mobile phone company to get precise timings of calls and see how these compared to the estimated time of the crash.

Drivers who had used a mobile phone, either holding it to their ear or using a hands-free system, were 4.1 times more likely to have an accident in the next 10 minutes than if they had not made a call.

The comparative risk with a hand-held phone was no less than 4.9 times, and with hands-free phones it was 3.8 times.

The study, published today online by the British Medical Journal, says the findings raise worrisome questions about the expanding use of hands-free technology, adopted by many drivers in response to safety messages or laws about using a hand-held phone while at the wheel.

"If this new technology actually increases mobile phone use in cars, it could contribute to even more crashes," the paper says.

The researchers say the next step is to see if certain types of hands-free devices, such as car kits or voice activated units, are safer than others.

Because of concerns about the risks of a potential crash, using a hand-held mobile phone while driving is illegal in the European Union, all Australian states, and selected states or provinces in the US and Canada.

Graham Chalker, chief executive officer of the Australian Mobile Telecommunications Association, says a hands-free device can reduce the physical effort to make and receive calls.

"However, drivers should also avoid making calls in heavy traffic or bad weather conditions and they should not engage in distracting, complex or emotional conversations," he says.

Tuesday, December 06, 2005


The truth about the Mobile virus scares

Some simple facts before proceeding to cabir, the nemisis you were told

Fact: no-one can pass a virus to your Symbian smartphone over Bluetooth or MMS without your knowledge. See Viruses for Symbian OS below for much more on this.

Fact: it's impossible for any piece of malicious software to make your smartphone unusable. Even if you allow a piece of 'malware' (i.e. a malicious program) onto your unit, it can't touch the OS and applications in ROM, which means you can always do a hard reset to get back to a working system.

(For hard reset, type in ‘*#7370#’ works with older Series 60 smartphones, 'Dial'+'*'+'3' while powering on for newer ones, procedures for UIQ and Series 80 units are in the manual) to get back to a working system.

Fact: the Symbian 'viruses' you read about aren't really in the wild, in the same way that Windows viruses are. Because it's realistically impossible for these apps to spread, you simply will not come across them in any significant number in the real world.

Fact: you're not going to pick up a worm through being online either, as Symbian OS's TCP/IP stack and port handling is far, far tighter than that (that used to be) used in Windows.

Fact: the biggest hazard in the Symbian world is the 'warez' scene, where unscrupulous people 'crack' commercial software and then put it up for free download or try to get friends to beam it around. Quite apart from the ethical considerations about putting genuine Symbian authors out of business, these cracked versions are the perfect opportunity for a malicious cracker to insert routines designed to cripple your phone or scramble your data. You can stay clear of such malware by downloading your Symbian OS third party software from trusted sources and staying clear of warez.

There really is no danger whatsoever of your Symbian OS smartphone becoming 'infected' with something without your knowledge. So sleep easy.

Now do you think, you need a Anti-virus program for your mobile ?

Related Readings:
Symbian resolute in face of mobile virus row:

Mobiles catch Cabir virus at world athletics:

Mobile phone viruses: 'Don't panic!' -- http://networks.silicon.com/mobile/0,39024665,39130139,00.htm

Viruses for Symbian OS - the truth -- http://3lib.ukonline.co.uk/viruses.htm

Excerpts from Original article by Steve Litchfield (www.allaboutsymbian.com)


Have you ever tried getting an application (or indeed any other kind of file) from one smartphone to another? Quite apart from the logistics of getting Bluetooth in the right mode ('Visibility: shown to all') on the recipient phone and getting the phones to actually find each other, anything request from another phone to send something has to be manually authorised (i.e. the recipient has to actively read the warning and press a button marked 'Yes'). And, for an application, there are many extra steps to agree to, in terms of accepting that you want to install it in the first place, that it probably hasn't been officially signed and then deciding which disk (internal or expansion card) to install to.

This is totally unlike the virus situation on desktop computers, where viruses infect you quickly and silently, reaching out to others via extra email transmissions and via direct Internet probes. Under Symbian OS, there is (so far) no known way for software to get sufficiently under the hood without your express permission to be able to do any of these things.

A Symbian targetted virus in the Real World

So you're walking through Paddington station, London, within Bluetooth reach of a hundred other smartphone users. And you've left your Nokia 6600 (or similar Series 60 smartphone) open to incoming Bluetooth connections because you often share contacts and appointments with colleagues and it's simply more convenient to leave this setting 'on'. All of a sudden, an 'infected' Series 60 smartphone (assuming there are any in the wild) reaches out to your phone and you hear a beep. Looking at the display you see

"Receive message via Bluetooth from Nokia 3660?"
with buttons marked 'Yes' and 'No'.

Your first choice should obviously be 'No', as you're not with a friend or colleague and are not expecting an incoming contact, appointment or file. Pressing 'No' means instantly stopping the incoming connection dead in its tracks. But let's say that you press 'Yes', out of curiosity perhaps. The virus application will be received into your Inbox, which may even automatically spot that it's a Symbian Installation (SIS) file and will start installing it. There's still no need to panic, though, as you'll then have to accept the various installation warnings and questions:

"Installation security warning: Unable to verify supplier. Continue anyway?"
with buttons marked 'Yes' and 'No'.

There's no application title shown yet, and perhaps you decide to carry on a little further, again out of curiosity (remember that you're not expecting anything).

Now we're getting to the nub of the matter. Symbian OS next pops up the question:

"Install Cabir?" (or "Sexxy", or whatever the heck today's media-favourite virus is called)
with buttons marked 'Yes' and 'No'.

At this point, if you still answer 'Yes', then you deserve everything you get! (As an aside, there are still at least two more questions to answer before the application is actually installed, giving you two more chances to back out)


Does the above sequence sound like the seamless and invisible mechanism needed by any decent virus if it's to propagate itself effectively in the wild? An emphatic NO.

You can keep your Symbian smartphone completely free of malware by following a couple of simple rules:

1) Don't accept unsolicited Bluetooth transmissions from other phones. Or trust applications tacked onto MMS messages ('e.g. Hey, try my new, kewl game!')

2) Don't install applications unless they are ones you've asked for or have downloaded from reputable software sites (Handango, AllAboutSymbian, My-Symbian, 3-Lib, etc.)

3) In most cases, it's quite safe to leave Bluetooth visibility as 'Shown to all'. If you do get bothered by too many unsolicited connection attempts, simply change the setting to 'Hidden'. Although given that the number of 'infected' Symbian Series 60 phones worldwide is truly tiny, you really don't have to worry! You're more likely to be hit by lightning or to win the lottery...

(C) 2004, 2005 Steve Litchfield

Friday, December 02, 2005


Google Sandbox Effect: What the hell is it ?

A site is sandboxed when it is new and does not rank for keyword phrases that are not incredibly competitive (such as a unique company name) in Google after making the page "search engine friendly" and after being indexed. This phenomenon, the techies describe as Google Sandbox Effect

A sandboxed site doesn't means a site that has not been indexed by Google. That is wrong. Sandboxed sites are very much so indexed by Google, but have a hard time ranking for keyword phrases, no matter how competitive they are.

Origin of the name:

Guys from Search Engine Roundtable found existence of some form of issue with Google and new sites. The first post was named New Sites = Poor Results in Google, that was before it had a name. In a WebmasterWorld thread linked to from the "New Sites = Poor Results in Google" entry, the term "sandbox" came about. Later on, guest author SEO Guy posted an entry here using that title The Sandbox Effect, which helped make its name

Does the sandbox really exist?

Google engineer Matt Cutts has essentially acknowledged that a sandbox effect exists and that it's a product of their algorithm, and at least one other anonymous Google engineer is reported to referred to a "probation" period for new sites. Despite some differences in terminology, the sandbox as an abstraction for a specific sum of parts in Google's larger algorithm is almost certainly existent.

How long are sites sandboxed?

The reported sandbox period is extremely variable; ranging from 3 months to indefinite, the typical range though seems around 6-9 months, and one Google engineer has reportedly stated the actual range is 6-12 months. Many have observed that the period appears to correlate with industry competitiveness/popularity, with the most popular and commercial industries having the longest "probation" period.

10 methods to bypass or escape the sandbox

Note: I've avoided listing methods aimed at only minimizing your time in the sandbox—as opposed to methods of actually escaping it—as those are basically paramount to good SEO practises, which is obviously way beyond the scope of this article.

Definition and origin borrowed from www.seroundtable.com
10 effective methods borrowed from www.webmasterbrain.com

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Thursday, December 01, 2005


Is Google Search Over Hyped?

Google is supposed to be the defacto queen of web search. Or so it look likes. Until now, even I thought so. Recent blind study finds not so. Is it a myth?

Guys from www.webmasterbrain.com began a Search Engine Experiment to discover which of the top search engines really offers the most relevant search results. With 5,000+ participants thus far, the below Pie reveal the results as they currently stand:

Most Relevant Graph

The modes operandi works like this -- the user is asked to key in a search string. Results are fetched from the three search engines branded as (brand x, y & z) and user is asked to judge which search engine is most relevant. The surprise is.......

Current results show Google offered 42% relevant results compared to 33% for Yahoo and 27% for MSN. This is not a great performance considering the close figures by yahoo & MSN and the much hype surrounding Google Search. Though, Google is clearly the leader, the margins are not so high to make it the defacto engine as perceived.

(Note: the image above is updated automatically, so you will probably be seeing newer figures than written).

They are planning to experiment indefinitely with the test results automatically updated every 15 minutes. The updated results will be shown in the images above and below.

Readers can take the blind test to find out which search engines' results you personally prefer.

Included is also a disclaimer that despite best efforts at making the test fair, and prevent cheating, they remind that by no means the accuracy of these test results can be gauranteed.

So watch out this blog.

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Tips for Searching Google

by Gary Price --> source: www.virtualchase.com

 Limiting by date can be a problem. Genie Tyburski and I wrote an article about this last year. Date searching is reliable only when Google can consistently identify them as it does with Usenet message (Google Groups) and news (Google News).

 A potentially useful way to limit the scope of a search is to use the syntax for file type (filetype:). For example, filetype:ppt google finds mention of Google in PowerPoint slides. Other formats include .pdf (Adobe Acrobat), .doc (Word) and .xls (Excel). Other search engines also let you query these formats.

 You can use an asterisk (*) as a wildcard. Example: "George * Bush" finds George W.
. Example: "To * * * to be" finds "To be or not to be". I've used this strategy to find email addresses: "email * * <domain>".

 Some documents are not completely indexed by Google. Indexing of the text in Web pages stops after 101kb (For PDF, it's 120kb.)

 Google limits the number of search terms to ten.

 Not every Google version offers all of Google's features. For example, Google via the Washington Post does not offer the cache or similar page options.

 Finding out who links to a Web page is popular. You use the link (link:) syntax. However, you
cannot limit the search using additional syntax. For example, you cannot discover which .edu sites link to the home page of The Virtual Chase. The search link:www.virtualchase.com site:edu does not work. AllTheWeb, on the other hand, lets you add additional syntax to a reverse link search.

 For the most part, search engines display one result per domain. For example, enter "competitive intelligence" "new york". Google returns two listings from SCIP. To see additional pages from the same domain -- scip.org, you have to click the "more results" link.

 Search terms are linked to dictionary definitions via Dictionary.com. Find the link near the top of the page in the blue bar. Other engines also offer this feature.

 Using Google UncleSam, limits your search to material from government sites.

 Findlaw also offers a focused version of Google. The filter boosts the relevancy of legal and government information. See LawCrawler.

 Google is wonderful, but it is not the only Web search tool. Take a look at Teoma, AllTheWeb and Vivisimo.

 Finally, learn about and bookmark specialized or, as a professor at Penn State calls them, niche databases. This can save you time and aggravation. Examples include the new keyword searchable version of The Wayback Machine or the even newer SMEALSearch, which indexes freely available, scholarly business information.

Gary Price (Gary Price Library Internet Research Consulting) is the author of the essential Weblog for searchers, The ResourceShelf.

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