What is GPS Survey: Learn the basics

GPS Satellite surveying usually involves relative positioning modes of operation, and in turn high accuracies. So, let us now discover what GPS survey is in a detailed manner, and analyze how GPS satellite surveying is different from a conventional GPS survey.

Basics of GPS Satellite Surveying

In GPS Satellite Surveying, the points of observation are considered coordinated as stationary, and the collected GPS data pertains to a specific "observation session.” Before we move towards the details, let us start with the significant features of GPS Satellite Surveying:

• GPS data collection is done instantly, thereby rendering a real-time solution.

• The positioning modes of operation can be either relative or absolute, involving relatively lower degrees of accuracy.

• All the measurements are usually done primarily based on PRN codes; hence, pseudo-range data processing becomes essential.

• With the application of this software, safe passage of aircraft and ships is ensured to the maximum extent.

• The measurements made on the L-band carrier wave, require special instrumentation and software associated with the traditional surveying and mapping functions.

Basic Instrumentation Set-uP Involved With a GPS Network Survey

The GPS network survey involves a number of fixed-height tripods, antennas, receiver sets, meteorological and minor scientific instruments.

Identical equipment is used whenever possible in order to nullify the equipment bias effects.

A validation survey is usually used to determine and demonstrate the compatibility of using a mixed bag of instrument models. Calibrations are done to all the equipments and possibilities of erroneous measurements are ruled out. Finally, validation survey serves as a starting point to start the proceedings of live GPS Survey.

Survey Planning Considerations

Survey planning considerations are usually based on following parameters:

Nature and Aim of Project: It is done just as in case of conventional GPS surveys.

Determining Unique Characteristics of GPS: This brings about severe simplification in survey design, and there are no requirements for station inter-visibility in particular.

Deciding Upon Total Number of Points to be Surveyed: This has always been one of the biggest logistical problems involved with a GPS Survey as the resources are at the surveyor’s disposal. Depending upon the strategy to be used for propagating the survey, a decision is made on the count.

Prudent Survey Practice: This involves check measurements and increases the level of redundancy in the network design, but it usually helps in obtaining better results.

Rapid Static GPS Surveying

Also referred to as quick-static or fast-static, the rapid static GPS survey has the following salient features, which tend to differ from the conventional ones.

Observation Time Requirements: The Observation times are significantly shorter in comparison to the conventional GPS surveying time. They are calculated as function of satellite geometry, number of satellites that are tracked, and the baseline length.

Baseline and Number of Satellites: In a typical GPS satellite surveying setup with four to six satellites and a baseline between five and 20 kms, receivers occupy baseline for five to 20 minutes, depending upon the value of baseline.

Hardware Requirements

Depending upon the GPS products involved with the survey, the hardware requirements may change to a considerable extent. In some cases, merely dual-frequency phase measurements may suffice, while surveys involving tedious measurements require accurate dual-frequency pseudo-range measurements as well.

Unlike conventional GPS surveys, the GPS Satellite Surveys requires lot of data processing, but the option of "mixing" of receivers has not been successfully devised to date.

The exact configuration of hardware to be used during the survey also greatly depends upon the tracking software being made use of. For instance, the rapid static GPS survey produces results with single frequency phase data. Hence, high-end hardware is not needed.

Specialised Software

The GPS Satellite Surveying heavily relies on the software to resolve the ambiguities (if any) and estimate their integer values, with the help of a relatively short observation period.

Varieties of software are available in market that can be used during different surveys involving variable levels of sophistication and peculiar characteristics. However, fast ambiguity resolution capability remains the primary requirement in all the cases.

Related Articles

For more information on using GPS in surveying, read the Bright Hub articles Handheld GPS Surveying Unit – Fast and Easy Survey, GPS Survey - Benefits of Using a GPS in Surveying and GPS Systems Used in Construction Surveying.

Tomtom vs. Nuvi: Which Should I Buy?

In the market for a GPS and having having trouble deciding between a TomTom GPS and a Nuvi GPS? We found that price is not the only issue. Follow along as we line the devices up feature-by-feature and try to pick a winner.

If you are in the market for a new (or a first) car based GPS system then you may find yourself in the middle of a debate. Should you get a TomTom GPS or a Nuvi? It may seem like it is an arbitrary choice, or one that you should make based solely on price. It is not, it is a decision you should base on well thought out research. Luckily for you, there is no need to spend hours scouring the web for that data. We have done somel of the basic leg work for you, with a head to head comparison of two of the basic models.

Why These Models?

The models that were chosen are a TomTom One and a Nuvi 1200. Granted, this is not a top of the line model for either of these brands. That choice was deliberate, since very few people are going to invest in a top of the line model for their first GPS. Not to mention that top of the line models can cost up to and over 500 dollars.

Screen Size

Screen size will be a factor for anyone who is worried about having vision problems. If you are vision impaired or simply nearsighted then you may want to make this a major factor. In this case however, both have a 3.5 inch screen.

Emergency Help

Your GPS should be able to help you get out of a jam. If it does not have some kind of emergency help, you should put it back on the shelf. Luckily, both the TomTom and the Nuvi model have a built in help feature. For the Nuvi model this is called, “Where am I” and it can help you to find hospitals, police stations or gas stations close to you. TomTom’s version is know as Emergency Menu and can help you find these facilities or get roadside assistance.

Compatability Issues

One factor that sips most people’s attention is compatibility with your computers operating systems. This may seem trivial, but if you want to be able to update your maps or use software compatibility. Luckily for you both the TomTom and the Garmin Nuvi are compatible with Windows XP, Windows Vista and any Mac OS 10.4 or above.

Route Calcualtions

Both models allow you to select a route by either shortest time or shortest distance, which is good to know. It is also good to know what is unique. The Nuvi has "eco route," which allows you to get the most fuel efficient route. The TomTom model has a feature know as, “Beat the traffic” which helps you to find alternate routes when you encounter a sea of brake lights.

So Which Should I Pick?

With so many useful (and similar features for both models, you may have a hard time choosing. That is why we will look at some differences. The Nuvi weighs less then the Tom Tom, and is slightly smaller. That means a space conscious user should choose the Nuvi. The advertised battery length is the same for both models. Since the Nuvi also allows for MSN Direct support and lets you make custom map changes, it may just be the way to go for everyone.

Now you can make an informed decision about which GPS model to buy. Go with what you feel would be best based on that information and anything else you feel is relevant.

Accuracy of GPS Navigation Receivers

GPS navigation systems are invaluable in travel, helping us find specific addresses and locations in unfamiliar areas. These systems need to be very accurate in order to do their job, but just how accurate are they?

Introduction

When commercial GPS receivers were first released, they were much less accurate than today's units. Typically, an early generation GPS receiver could only locate your position within 100 meters. That kind of accuracy might be OK if you're looking for a large building or landmark, or need to know what part of town you're in, but you can forget looking for, say, a specific car in a parking lot.

The thing is, this 100 meter accuracy wasn't a limitation of the GPS network, it was an intentional obfuscation set up by the government called Selective Availability. No, this isn't a conspiracy theory: in the early days of GPS, the military didn't want unfriendly nations to be able to have the same advantage as the US when it came to GPS, so they programmed the satellites not to give the most accurate positioning data to non-military GPS units.

Accuracy Improvements

A system called Differential GPS was eventually developed to improve the accuracy of GPS units to around 10 meters. DGPS used a network of reference stations to more accurately calculate the GPS receiver's position. This made the system much more suitable for precise navigation. After the year 2000, the government disabled Selective Availability for commercial GPS units, and the accuracy was once more improved to about 5 meters.

However, while plenty accurate for most users, this still wasn't good enough for the FAA's standards of aircraft navigation, and a new system, called the Wide Area Augmentation System, was developed. The WAAS works similarly to DGPS, but can offer GPS precision within 1 meter. WAAS has some disadvantages, however, such as only being available in North America.

Conclusion

Today's GPS navigation receivers are much more accurate than early models, and with systems like Differential GPS, can typically offer precision within 10 meters. This level of accuracy is great for vehicular navigation, even when trying to find specific addresses. It also makes activities like Geocaching possible with commercial GPS receivers.

GPS systems will likely continue to become more and more accurate, with other continents developing systems like the North American WAAS, which makes <1>

GPS Simplified

Still entangled in the web of GPS? Here we give you a quick guide to help you understanding the intricacies of GPS - what it is, how it works, and how important a GPS Receiver is. We will try to explain these concepts as simply as possible.

Global Positioning System or GPS is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. It was created to serve military purposes at first, but then in the 1980s the U.S. government made it available for public use. Whether for military or public use, GPS serves one main purpose - navigation.

How Does GPS Work?

It is unavoidable to be technical when describing how GPS works. It is a radio-navigation system consisting of 24 satellites orbiting the earth, and their respective ground stations. To calculate a position, these satellites serve as reference points when calculating positions relative to a matter of meters.

In other words, GPS triangulates the position of a satellite, its ground station and the area you want to locate. However, this is done in a more scientific and finite measurement of travel time, distance, signal experiences, and atmospheric delays.

To measure GPS points, you must use a GPS receiver that calculates its position by the signals transmitted to the satellites. These satellites send messages containing information such as the time the message was sent and the satellites orbital information. Once it receives this information, the GPS receiver will then measure the transit time of the sent message and calculate the distance of the GPS receiver to the each of the satellites.

The location is then displayed through GPS maps.

What is a GPS Receiver?

As stated, GPS is only useful if you have a GPS receiver. Fortunately, there are many GPS receivers on the market. There are important features that you should look for when shopping for a GPS receiver.

One GPS receiver feature is turn-by-turn navigation, such as driving directions and route instructions. This is a useful feature since it frees your hands while driving, as the GPS receiver gives spoken directions.

Another feature to look for in a GPS receiver is Bluetooth technology. If you have a Bluetooth, you can practically use the GPS receiver as your mobile phone if you connect it via Bluetooth.

Other important features that you should look for in a GPS receiver include an integrated traffic receiver, screen size, points of interest, and memory card storage.

Conclusion

There are certainly other concepts and jargons that you need to learn before you fully understand the ins and outs of GPS. Other important concepts to look into include geocaching, digital maps, digital mapping, waypoints and other related information. Although knowing these concepts is not essential, it would not hurt to learn them if you are serious about getting into GPS and its components.

Check out the Bright Hub GPS Navigation Systems channel for tutorials and articles on these topics and more.

Garmin Fishfinder Tranducers: Worthy Fishing Companions

Garmin Fishfinder Transducers are the ultimate non-human companion for your fishing expeditions on a boat. These devices combine Global Positioning System technology with the ability to determine and display on a digital screen where fish are when traversing any body of water. Find out more below.

How Does Sonar Work to Find the Fish on a Garmin?

A transducer, in general, is any kind of device that converts energy of one type into energy of another type. What we’re essentially talking about here can be explained as converting the presence of the fish that is within the parameters of the fishfinder’s cone of detection, under the boat, to a digital facsimile of the fish on the display reader board topside. The Garmin Fishfinder display is fastened next to the steering wheel so the boat operator can maneuver the boat to optimize the chances of catching the fish which is, of course, the object of this technology. Knowing where the fish are down there doesn’t guarantee you’ll catch fish, however. You’ll still need human ingenuity and fishing skills to land them no matter how easy the machines are making it these days.

All fish finders operate by using Sonar (an abbreviation of SOund, NAvigation and Ranging), the same technology developed for submarines to navigate in deep water during WWII. If you’ve ever seen a movie about submarines, you’ll recognize sonar as that intermittent but constant “ping” noise. Sonar uses sound waves to determine where objects are in the water, just like a bat uses sound waves to locate and eat flying insects and to keep from crashing into trees and buildings unceremoniously.

Sonar emitted from the transmitter component of the fish finder travels downward from the boat to the ocean, bay, sound, marsh, or lake floor like the cone-shaped beam of a flashlight. So the beam, or sound wave, sent from the fish finder source becomes an increasingly larger wave in every direction as it travels away from its source. Anything that the beam hits, hopefully a fish, gets bounced back to the fishfinder through the transducer to be converted back to an electrical impulse in order to appear on the screen in the symbol of a fish.

The fishfinder approximates where the fish are by measuring the amount of time between when the beam was sent out and when it registered the hit. In this same manner, the fishfinder can tell you how far down the bottom is, too, because it always bounces the beam off the bottom. The readout constantly tells you how deep the water is and what kind of structure is down there, like the rocky habitat some fish like to feed in, for instance. These are critical components for both the safety of your boat and in finding where the fish like to congregate and conspire to elude you.

Garmin Accuracy and Innovation Leads You to the Fish

Traditionally, the boat would have to be right on top of your prey but with advances in technology these Garmin fishfinders allow you to see what’s off to the side of the boat too by expanding that cone of detection. Increasing the coverage increases the price. The high resolution display screens have come a long way also and resemble nautical charts and decent looking maps. Even the relative sizes of fish or schools of fish swimming nearby appear on the readout. Since you are linked to a satellite, the mapped shorelines are displayed as well. In days of old, fishfinders resembled something rather lame like a blipping Atari video screen.

The Garmin features technology called Ultrascroll™ which means the display keeps up with your speed by constantly refreshing to maintain the best accuracy of what you’re passing over. That’s great for trolling, a highly productive means of fishing for Marlin or Tuna. Incidentally, Garmin makes plenty of models for freshwater and the shallows you’ll likely find there as well. These are usually smaller and more compact units depending upon the type of freshwater you’ll be fishing. The newer models of Garmin Fishfinder Transducers are far more user friendly with less buttons and more intuitive applications. Convenient alarms are built in, sounding off in extremely shallow water or when your fishfinder battery is running low.

The Garmin Fishfinder on my friend’s boat was extremely useful in fishing for Striped Bass and Tuna off the coast of Cape Cod, in the Vineyard Sound and along the Elizabeth Islands. When the Stripers are making their solo runs in the fall, there’s obviously a whole ocean out there for them to run and the Garmin helps you find them. When they appear on the screen, there is an exciting scramble and call to action in the boat, especially when it looks like a huge monster of fish is close by.

Not only that, but that is some very tricky sea to operate in and the Garmin’s capability to pinpoint where the rocks were in that shallow water were crucial in keeping the boat out of harm’s way so we could concentrate on fishing. These devices double as excellent navigational aids. Since the display on most models also tracks the coast line when you’re close to shore, you can imagine how helpful that is in deep fog. It also pinpoint’s prominent structures on land such as towers to aid you in navigation when the skies are clear.

Cell Phone Navigation vs. Portable GPS

The portable GPS market is facing stiff pressure from the competition of the growing popularity of cell phones with GPS navigation functionality. Here's a brief comparison of these two navigation systems to help you decide which one to use.

Cell Phone Navigation

Because of the FCC mandated E911 program which required cell phone manufacturers to integrate GPS receivers in their cell phone units, cell phone manufacturers today have made it a standard to have GPS navigation as one of their cell phones' major attractions. GPS-enabled cell phones allow you to view and listen to turn-by-turn directions provided by the cellular provider. Cell phones with GPS navigation features are usually loaded with GPS chips that support A-GPS (or Assisted GPS). However, to use the A-GPS feature, cell phone users must subscribe to their cellular providers GPS-services bundle.

Equipped with a cell phone with the A-GPS feature and subscribed to a cellular provider's GPS navigation services, users can receive driving directions on the their cell phones. These driving directions are fully automated and calculated, so much so that when you miss a turn, the driving directions will adjust accordingly and give you new directions to use to get to where you are heading.

*Example of a cell phone with navigation feature - Nokia N95

Advantages and Disadvantages of Cell Phone Navigation

GPS equipped cell phones offer faster re-routing directions, updated traffic conditions and other location-based features including social networking. In addition, cell phones are affordable even if an A-GPS is included as one of their features. Even the data plans offered by Telco carriers with GPS features are very affordable.

Best of all, cell phone GPS information is quickly and easily updated on a regular basis. On the downside, cell phones have smaller screens so sometimes reading the routes is a pain and the chances of you getting lost is highly probable especially if you are not used to map reading.

Portable GPS

The portable GPS which takes the popular form of in-car GPS navigation systems are specialized gadgets made for the sole purpose of providing you with navigational information. These devices are commonly mounted to your car’s dashboard and run software that tells you the right route to take when going from one place to another. The software can be updated to include new routes and traffic conditions. In-car GPS navigation systems are very efficient for as long as you stay on the road. If you start to stray from the road, the GPS system will prompt you to go back, and stay driving on the road. When you miss a turn or get lost, the in-car GPS system will tell you of your conditions right away.

*Photo example of a Portable GPS - TomTom ONE 125 3.5-Inch Portable GPS Navigator

Advantages and Disadvantages of Portable GPS

Portable GPS devices generally have bigger screens than cell phones, so the chance of you reading the directional routes properly is much better. However, the hardware cost is higher than using a cell phone with GPS capability. Upgrading maps and the list of business establishments is also quite expensive, but is a must for portable GPS owners, unless they don't mind getting lost due to outdated information.

Conclusion

After knowing the basics of both cell phone navigation and portable GPS navigation, the question of which system is better still depends on your needs and preferences. Portable GPS devices are starting to feel the competition being posted by cell phones with assisted navigation features. Cell phone navigation is less costly and you can bring it with you anywhere. An added point is the fact that cell phones have other uses aside from GPS navigation.

But we still could not discount the fact that portable GPS navigation is still more reliable and dependable for the simple reason that these devices were built solely for navigation purposes. There may be additional costs, but in the long run, with its reliable and dependable information, the portable GPS device's navigation advantages outweighs its disadvantages.

Commonly Used Portable GPS Terms

Here's a follow-up to our GPS Simplied feature. This time we give you some of the most commonly used acronyms used in portable GPS as well as a brief explanation of what each term means.

Terms for Portable GPS

A-GPS (Assisted Global Positioning System) - a technology which utilizes an assistance server to reduce the time in determining a location using GPS.

CORS (Continuously Operating Reference Stations) - a network of sites that provides Global Navigation Satellite System coordinated by the U.S. National Geodetic Survey.

EGNOS (European Geostationary Navigation Overlay Service) - Europe's first satellite navigation venture that extends the US GPS and Russian GLONASS military satellite navigation systems, making them suitable various critical applications.

GIS (Geographic Information System) - a system that interprets and visualizes data that reveal relationships, patterns, and trends through maps, globes, charts, and reports.

GPS (Global Positioning System) - a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense.

GPRS - General Pocket Radio Service - a packet-based wireless communication service which can provide up to 114kbps Internet connection for mobile phones and computers.

GBAS (Ground Based Augmentation System) - a safety-critical system that extends the GPS Standard Positioning Service by enhancing its service levels.

MSAS (Multi-functional Satellite Augmentation System) - a Japanese satellite navigation system that supports Differential GPS to augment the GPS system by reporting the reliability and accuracy of its signals.

NDGPS (Nationwide Differential GPS) - a system that provides differential correction based on a known location of a GPS reference station antenna.

PNA/PND (Personnel Navigation Assistant/Device) - any portable electronic product which combines GPS and navigation functions.

POI (Points of Interest) - any specific location point that is useful or interesting to an individual.

RDS-TMC (Radio Data System-Traffic Message Channel) - a system that provides traffic and travel delay data to a driver through Radio Data Systems broadcasted through FM radio waves.

RINEX (Receiver Independent Exchange Format) - a data interchange format used in satellite navigation system data that allows post-processing to produce a more accurate solution.

SBAS (Space-Based Augmentation System) - systems that support wide-area or regional augmentation using satellite-broadcast messages comprised o multiple ground stations.

TTFF (Time to First Fix) - specifies the time required for a GPS receiver in acquiring satellite signals and navigation data.

WAAS (Wide Area Augmentation System) - an air navigation aid that augments GPS to improve accuracy, availability and integrity.