GPS Primer - Revision history

Mparadis: /* Speed and Altitude Limits */

2012-12-12T18:21:37Z

Speed and Altitude Limits

← Older revision		Revision as of 18:21, 12 December 2012
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	===Speed and Altitude Limits===		===Speed and Altitude Limits===

	Commercial GPS chips are limited to a maximum of 515 m/s at 18,000 meters. This limitation is an industry standard first introduced by CoCom during the beginning of the Cold War, and has been adopted by the U.S. Department of Commerce to this day. When a GPS module reaches these limits, it will cease signal acquisition until the unit has dropped below the limits. Some chips, like the one used on the [[1040 User Guide\|1040 - PhidgetGPS]] will only cease acquisition when both of these limits are exceeded.		Commercial GPS chips are limited to a maximum of 515 m/s at 18,000 meters altitude. This limitation is an industry standard first introduced by CoCom during the beginning of the Cold War, and has been adopted by the U.S. Department of Commerce to this day. When a GPS module reaches these limits, it will cease signal acquisition until the unit has dropped below the limits. Some chips, like the one used on the [[1040 User Guide\|1040 - PhidgetGPS]] will only cease acquisition when both of these limits are exceeded.

	==GPS Antenna==		==GPS Antenna==

Mparadis: /* Signal Acquisition */

2012-12-12T18:19:46Z

Signal Acquisition

← Older revision		Revision as of 18:19, 12 December 2012
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	===WAAS===		===WAAS===
	WAAS or Wide Area Augmentation System is a system designed to increase the capabilities of the GPS system. The intention was to improve the accuracy and reliability to increase the usability of GPS in aircraft. WAAS works by using a network of ground based GPS stations that measure differences in the GPS satellite's signals and are used to give correction factors to WAAS satellites. The WAAS satellites broadcast the correction signals and WAAS capable GPS receivers can pick them up and use them to increase the accuracy of their readings.		WAAS or Wide Area Augmentation System is a system designed to increase the capabilities of the GPS system. The intention was to improve the accuracy and reliability to increase the usability of GPS in aircraft. WAAS works by using a network of ground based GPS stations that measure differences in the GPS satellite's signals and are used to give correction factors to WAAS satellites. The WAAS satellites broadcast the correction signals and WAAS capable GPS receivers can pick them up and use them to increase the accuracy of their readings.

			===Speed and Altitude Limits===

			Commercial GPS chips are limited to a maximum of 515 m/s at 18,000 meters. This limitation is an industry standard first introduced by CoCom during the beginning of the Cold War, and has been adopted by the U.S. Department of Commerce to this day. When a GPS module reaches these limits, it will cease signal acquisition until the unit has dropped below the limits. Some chips, like the one used on the [[1040 User Guide\|1040 - PhidgetGPS]] will only cease acquisition when both of these limits are exceeded.

	==GPS Antenna==		==GPS Antenna==

Burley: /* Time Accuracy */

2012-10-25T15:32:16Z

Time Accuracy

← Older revision		Revision as of 15:32, 25 October 2012
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	==Position Accuracy==		==Position Accuracy==
	Even at the best of times commercial GPS units are not exceptionally accurate, often having an accuracy of several meters. For example, the PhidgetGPS is listed as having a position accuracy of 2.5m CEP (circular error of probability) but that is only in a situation where the antenna is located in a field with no tall buildings around, no clouds in the sky, etc... In a more typical environment you can expect the CEP to be larger.		Even at the best of times commercial GPS units are not exceptionally accurate, often having an accuracy of several meters. For example, the PhidgetGPS is listed as having a position accuracy of 2.5m CEP (circular error of probability) but that is only in a situation where the antenna is located in a field with no tall buildings around, no clouds in the sky, etc... In a more typical environment you can expect the CEP to be larger.

	~~==Time Accuracy==~~
	The PhidgetGPS is rated at having a maximum error of 300ns. This is a bit misleading as this does not refer to the time that the GPS outputs with its data. Rather, it refers to the timing error when it compares the local time to the satellites time. This is done as part of the GPS coordinates calculate and is very important to the accuracy of the position data.

Burley: /* Position Accuracy */

2012-10-25T15:27:40Z

Position Accuracy

← Older revision		Revision as of 15:27, 25 October 2012
Line 29:		Line 29:
	==Position Accuracy==		==Position Accuracy==
	Even at the best of times commercial GPS units are not exceptionally accurate, often having an accuracy of several meters. For example, the PhidgetGPS is listed as having a position accuracy of 2.5m CEP (circular error of probability) but that is only in a situation where the antenna is located in a field with no tall buildings around, no clouds in the sky, etc... In a more typical environment you can expect the CEP to be larger.		Even at the best of times commercial GPS units are not exceptionally accurate, often having an accuracy of several meters. For example, the PhidgetGPS is listed as having a position accuracy of 2.5m CEP (circular error of probability) but that is only in a situation where the antenna is located in a field with no tall buildings around, no clouds in the sky, etc... In a more typical environment you can expect the CEP to be larger.

			==Time Accuracy==
			The PhidgetGPS is rated at having a maximum error of 300ns. This is a bit misleading as this does not refer to the time that the GPS outputs with its data. Rather, it refers to the timing error when it compares the local time to the satellites time. This is done as part of the GPS coordinates calculate and is very important to the accuracy of the position data.

Burley: /* WAAS */

2012-08-14T20:47:54Z

WAAS

← Older revision		Revision as of 20:47, 14 August 2012
Line 22:		Line 22:

	===WAAS===		===WAAS===
	WAAS or Wide Area Augmentation System is system designed to increase the capabilities of the GPS system. The intention was to improve the accuracy and reliability to increase the usability of GPS in aircraft. WAAS works by using a network of ground based GPS stations that measure differences in the GPS satellite's signals and are used to give correction factors to WAAS satellites. The WAAS satellites broadcast the correction signals and WAAS capable GPS receivers can pick them up and use them to increase the accuracy of their readings.		WAAS or Wide Area Augmentation System is a system designed to increase the capabilities of the GPS system. The intention was to improve the accuracy and reliability to increase the usability of GPS in aircraft. WAAS works by using a network of ground based GPS stations that measure differences in the GPS satellite's signals and are used to give correction factors to WAAS satellites. The WAAS satellites broadcast the correction signals and WAAS capable GPS receivers can pick them up and use them to increase the accuracy of their readings.

	==GPS Antenna==		==GPS Antenna==

Burley: /* Interference */

2012-08-14T20:46:31Z

Interference

← Older revision		Revision as of 20:46, 14 August 2012
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	If you are having trouble getting the device to acquire a position fix and give you a reliable position, try moving outdoors into an open area, where most of the sky is visible; this allows the unit to calculate your current position much faster.		If you are having trouble getting the device to acquire a position fix and give you a reliable position, try moving outdoors into an open area, where most of the sky is visible; this allows the unit to calculate your current position much faster.

			===WAAS===
			WAAS or Wide Area Augmentation System is system designed to increase the capabilities of the GPS system. The intention was to improve the accuracy and reliability to increase the usability of GPS in aircraft. WAAS works by using a network of ground based GPS stations that measure differences in the GPS satellite's signals and are used to give correction factors to WAAS satellites. The WAAS satellites broadcast the correction signals and WAAS capable GPS receivers can pick them up and use them to increase the accuracy of their readings.

	==GPS Antenna==		==GPS Antenna==

Burley: /* Position Accuracy */

2012-08-03T16:45:59Z

Position Accuracy

← Older revision		Revision as of 16:45, 3 August 2012
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	==Position Accuracy==		==Position Accuracy==
	Even at the best of times commercial GPS units are not exceptionally accurate, often having an accuracy of several meters. For example, the PhidgetGPS is listed as having a position accuracy of 2.5m CEP (circular error of probability) but that is only in a situation where the antenna is located in a field with no tall buildings around, no clouds in the sky, etc... In a more typical environment you can expect the CEP to be ~~much~~ larger.		Even at the best of times commercial GPS units are not exceptionally accurate, often having an accuracy of several meters. For example, the PhidgetGPS is listed as having a position accuracy of 2.5m CEP (circular error of probability) but that is only in a situation where the antenna is located in a field with no tall buildings around, no clouds in the sky, etc... In a more typical environment you can expect the CEP to be larger.

Burley: /* Products that fall under this category */

2012-08-03T16:45:13Z

Products that fall under this category

← Older revision		Revision as of 16:45, 3 August 2012
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	==Position Accuracy==		==Position Accuracy==
	Even at the best of times commercial GPS units are not exceptionally accurate, often having an accuracy of several meters. For example, the PhidgetGPS is listed as having a position accuracy of 2.5m CEP (circular error of probability) but that is only in a situation where the antenna is located in a field with no tall buildings around, no clouds in the sky, etc... In a more typical environment you can expect the CEP to be much larger.		Even at the best of times commercial GPS units are not exceptionally accurate, often having an accuracy of several meters. For example, the PhidgetGPS is listed as having a position accuracy of 2.5m CEP (circular error of probability) but that is only in a situation where the antenna is located in a field with no tall buildings around, no clouds in the sky, etc... In a more typical environment you can expect the CEP to be much larger.

	~~==Products that fall under this category==~~
	*[[1040 - PhidgetGPS]]

Burley: /* GPS Antenna */

2012-08-03T16:45:07Z

GPS Antenna

← Older revision		Revision as of 16:45, 3 August 2012
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	==GPS Antenna==		==GPS Antenna==
	A number of variables can affect the overall performance of the GPS antenna: avoid putting the antenna very close to electronics or motors of any sort, as well as power transmitters such as WIFI antennas.		A number of variables can affect the overall performance of the GPS antenna: avoid putting the antenna very close to electronics or motors of any sort, as well as power transmitters such as WIFI antennas. The best location for an antenna is an elevated position with as clear a view of the open sky as possible.

	==Position Accuracy==		==Position Accuracy==

Burley: /* Signal Acquisition */

2012-08-03T16:44:02Z

Signal Acquisition

← Older revision		Revision as of 16:44, 3 August 2012
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	==Signal Acquisition==		==Signal Acquisition==
	Acquiring a satellite fix the first time ~~the device~~ is started up can take 5-6 minutes.		Acquiring a satellite fix the first time a receiver is started up can take 5-6 minutes. Phidgets GPS devices have a battery on board that can enable “hot starts.” What this means is that the GPS is capable of remembering the most recent position of good satellites and will check there again when it is reconnected. With a live battery installed GPS signal reacquisition can as fast as 1 second. The speed of hot starts is dependent on how long it has been since the device was last started up as well as how far the device has been moved since it was last active. The longer it has been the less effective the hot start will be, generally they take less than 5 seconds though. If the device has been disconnected for longer than a day or two, the device will likely take the full 5-6 minutes to reacquire.
	~~Many~~ GPS devices have a battery on board that can enable “hot ~~starts” by~~ remembering the most recent position of ~~a satellite~~ and ~~checking that region first~~.
	With a live battery installed GPS signal reacquisition can as fast as 1 second ~~or even better~~.
	The speed of hot starts is dependent on how long it has been since the device was last started up.
	The longer it has been the less effective the hot start will be~~. Generally~~ they take less than 5 seconds though.
	If the device has been disconnected for longer than a day or two, the device will likely take the full 5-6 minutes to reacquire.

	The ability of a GPS to acquire a signal depends greatly on the environment or type of building you are in. ~~Generally, signal~~ strength indoors is vastly ~~reduced~~. Commercial/industrial buildings and high rises are much worse than a single story house due partly ~~to size~~ and partly to using steel studs in the walls ~~as opposed to~~ wooden. Moving close to a window should give you a stronger signal. If you are still unable to get a GPS signal, try using another GPS unit at the same location to verify that there are readable satellites in the area.		===Interference===
			The ability of a GPS to acquire a signal depends greatly on the environment or type of building you are in. Signal strength indoors is vastly degraded. Commercial/industrial buildings and high rises are much worse than a single story house due partly because they are larger and consequently have more intervening material and partly due to using steel studs in the walls rather than wooden. Moving close to a window should give you a stronger signal. If you are still unable to get a GPS signal, try using another GPS unit at the same location to verify that there are readable satellites in the area.

	If you are having trouble getting the device to acquire a position fix and give you a reliable position, try moving outdoors into an open area, where most of the sky is visible; this allows the unit to calculate your current position much faster.		If you are having trouble getting the device to acquire a position fix and give you a reliable position, try moving outdoors into an open area, where most of the sky is visible; this allows the unit to calculate your current position much faster.