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1. What is satellite trajectory?
The GPS Global Positioning and Navigation System has 24 GPS satellites orbiting the earth along six orbits (each group of four). Generally, there are no more than 12 satellites on the same side of the earth. Most GPS receivers can track 8 to 12 satellites. . Calculating LAT / LONG (2-dimensional) coordinates requires at least 3 satellites. Add one more piece to calculate 3D coordinates. For a given location, the GPS receiver knows which satellites are nearby at this time, because it constantly receives update signals from the satellites.
2. What is a parallel channel?
Some consumer GPS devices have 2 to 5 parallel channels to receive satellite signals. Because up to 12 satellites may be visible (the average is 8), this means that the GPS receiver must access each satellite in order to obtain information about each satellite.
Most GPS receivers on the market are 12 parallel channel type and 20 parallel channel type (Mio269, etc.), which allows them to continuously track the information of each satellite. The advantages of the 12-channel receiver include rapid cold start and initialization of satellite information, and better reception in forest areas. Generally, a 20-channel receiver does not require an external antenna, but an external antenna is still required in a closed space such as a cabin or a cabin to ensure accurate reception of GPS signals.
3. What is positioning time?
The positioning time refers to the time required for the receiver to determine the current position when the GPS receiver is restarted. For a 20-channel receiver, if you are near the location of the last positioning, the positioning time during cold start is generally 3 to 5 minutes, and 15 to 30 seconds for hot start.
Note:
Cold start: when it is used for the first time; when the battery is exhausted and the ephemeris information is lost; when the power is off, the receiver is moved more than 1000 kilometers.
Hot start: the start is less than two hours before the last positioning.
Warm start: Start more than two hours before the last positioning.
4. How is the current GPS positioning accuracy?
GPS requires three satellites for accurate positioning, but because the satellite clock frequency and receiver frequency are different (the satellites use rubidium and cesium clocks, the accuracy is very high, and the GPS receiver's clock accuracy is very low), so at least Four satellites can achieve positioning.
GPS was established for military purposes in the United States, and its current applications are also divided into two areas: military and civilian. From a technical point of view, due to technological progress, the accuracy of GPS can reach centimeters or even higher. At present, the US military GPS can reach the centimeter level.
In terms of civilian use, positioning accuracy has been greatly improved through GPS differential technology. Without interference, the positioning accuracy of most civilian GPS satellite positioning devices is about 2.93m ~ 29.3m.
5. What is the DGPS function?
Differential GPS (DGPS) is to form a base station by installing a high-precision GPS receiver at a location where the position is accurately measured. The position measured by the base station receiving the GPS satellite signal is compared with the known position of the station to obtain the position measurement error or pseudorange measurement error, and these errors are broadcast as correction values ​​to the surrounding space.
The GPS user receiver near the base station receives the correction signal from the base station and corrects its own GPS measurement value, thereby greatly improving the positioning accuracy. Many GPS equipment providers have set up DGPS transmitters in some regions for free use by customers with GPS receivers with DGPS capabilities.
6. In addition to considering positioning and navigation performance, what should we consider when purchasing GPS?
When purchasing a GPS device, the user must also consider some physical indicators in addition to the navigation performance. With the continuous development of navigation technology, especially the emergence of Sirf's third-generation navigation chip, GPS products have further improved in navigation performance, so that the new generation of GPS products have little difference in positioning and navigation performance. In addition to looking at product positioning and navigation performance when purchasing a product, physical indicators such as product size, weight, display screen, waterproof, shockproof, dustproof performance, high temperature resistance, and power consumption are also considered.
For those who buy GPS for the first time, they need to understand some GPS performance indicators in order to understand the product performance and make a suitable choice. The following is a brief introduction to some important GPS performance indicators.