Gps pathfinder office not measuring distance

Gps pathfinder office not measuring distance code#

If a fast time to first fix (TTFF) is needed, it is possible to upload a valid ephemeris to a receiver, and in addition to setting the time, a position fix can be obtained in under ten seconds. Variability in solar radiation pressure has an indirect effect on GPS accuracy due to its effect on ephemeris errors. While the ephemeris data is transmitted every 30 seconds, the information itself may be up to two hours old. When the GPS antenna is moving, the false solutions using reflected signals quickly fail to converge and only the direct signals result in stable solutions. Multipath effects are much less severe in moving vehicles. Short delay reflections are harder to filter out because they interfere with the true signal, causing effects almost indistinguishable from routine fluctuations in atmospheric delay. To address shorter delay multipath from the signal reflecting off the ground, specialized antennas (e.g., a choke ring antenna) may be used to reduce the signal power as received by the antenna.

For long delay multipath, the receiver itself can recognize the wayward signal and discard it. ДЄ variety of techniques, most notably narrow correlator spacing, have been developed to mitigate multipath errors. These delayed signals cause measurement errors that are different for each type of GPS signal due to its dependency on the wavelength. GPS signals can also be affected by multipath issues, where the radio signals reflect off surrounding terrain buildings, canyon walls, hard ground, etc. Its effect varies with local temperature and atmospheric pressure in quite a predictable manner using the laws of the ideal gases. The Atmospheric pressure can also change the signals reception delay, due to the dry gases present at the troposphere (78% N2, 21% O2, 0.9% Ar.). These traits make precise measurement and compensation of humidity errors more difficult than ionospheric effects. This effect is more localized than ionospheric effects, changes more quickly and is not frequency dependent. Humidity also causes a variable delay, resulting in errors similar to ionospheric delay, but occurring in the troposphere. The ionospheric data are transmitted via satellite in Satellite Based Augmentation Systems (SBAS) such as Wide Area Augmentation System (WAAS) (available in North America and Hawaii), EGNOS (Europe and Asia), Multi-functional Satellite Augmentation System (MSAS) (Japan), and GPS Aided Geo Augmented Navigation (GAGAN) (India) which transmits it on the GPS frequency using a special pseudo-random noise sequence (PRN), so only one receiver and antenna are required. Several systems send this information over radio or other links to allow L1-only receivers to make ionospheric corrections. This correction is also valid for other receivers in the same general location.

Those for any particular geographical area can be easily calculated by comparing the GPS-measured position to a known surveyed location. The effects of the ionosphere generally change slowly, and can be averaged over time. It allows a direct comparison of the L1 and L2 signals using the coded signal instead of the carrier wave.

Gps pathfinder office not measuring distance code#

To facilitate this on lower cost receivers, a new civilian code signal on L2, called L2C, was added to the Block IIR-M satellites, which was first launched in 2005. This can be done in civilian receivers without decrypting the P(Y) signal carried on L2, by tracking the carrier wave instead of the modulated code. Some military and expensive survey-grade civilian receivers calculate atmospheric dispersion from the different delays in the L1 and L2 frequencies, and apply a more precise correction. This phenomenon is known as dispersion and can be calculated from measurements of delays for two or more frequency bands, allowing delays at other frequencies to be estimated. It arises from ionized atmosphere (see Total electron content). Ionospheric delay of a microwave signal depends on its frequency. Once the receiver's approximate location is known, a mathematical model can be used to estimate and compensate for these errors. These effects are smallest when the satellite is directly overhead and become greater for satellites nearer the horizon since the path through the atmosphere is longer (see airmass).

Correcting these errors is a significant challenge to improving GPS position accuracy. Inconsistencies of atmospheric conditions affect the speed of the GPS signals as they pass through the Earth's atmosphere, especially the ionosphere. There is also a numerical error with an estimated value, Пѓ n u m or about 30 centimeters. User equivalent range errors (UERE) are shown in the table. Geometric Error Diagram Showing Typical Relation of Indicated Receiver Position, Intersection of Sphere Surfaces, and True Receiver Position in Terms of Pseudorange Errors, PDOP, and Numerical Errors