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How does satellite geometry affect GPS accuracy?

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GPS accuracy depends on many factors, such as signal quality, atmospheric conditions, and receiver performance. But one of the most important and often overlooked factors is satellite geometry. Satellite geometry refers to the relative positions of the satellites that are used to calculate your location. In this article, you will learn how satellite geometry affects GPS accuracy and how to measure it using a simple indicator called Dilution of Precision (DOP).

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Jean Claude NIYOMUGABO

120K+ Followers | LinkedIn Influencer | Leveraging the power of digital technology to improve the livelihoods of…
Benjamin Fostaty

Technical Support at Lotek Wireless

1 What is DOP?

DOP is a measure of how well the satellites are arranged to provide accurate location information. It is calculated from the angles between the satellites and your receiver. A low DOP means that the satellites are well spaced and form a large triangle or polygon around your receiver. This gives you a more precise location estimate. A high DOP means that the satellites are close together or aligned in a line or plane. This gives you a less precise location estimate and increases the potential error.

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Jean Claude NIYOMUGABO

120K+ Followers | LinkedIn Influencer | Leveraging the power of digital technology to improve the livelihoods of people| | Digital Communication Specialist | CEO of Agirite
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Satellite geometry significantly influences GPS accuracy. Optimal accuracy is achieved when satellites are widely distributed, minimizing triangulation errors. For instance, in urban canyons with tall buildings, satellite signals may bounce off structures, causing multi-path interference and degrading accuracy due to poor geometry. Therefore, open-sky environments tend to yield better GPS performance.

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Benjamin Fostaty

Technical Support at Lotek Wireless
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When navigation data sent from different GPS satellites shares a large intersection of potential error, the effect on the output location's potential error is increased. When these satellites are far apart, the intersection of their beams are minimized, which reduces the potential area where the receiver is located, and therefore error.

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2 How does DOP affect GPS accuracy?

The DOP value affects the accuracy of your location by multiplying the errors from other sources, such as signal noise, clock bias, or atmospheric delay. For example, if the error from these sources is 5 meters and the DOP value is 2, the resulting error in your location is 10 meters. If the DOP value is 10, the resulting error is 50 meters. Therefore, a lower DOP value means a higher GPS accuracy and vice versa.

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Benjamin Fostaty

Technical Support at Lotek Wireless
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DOP is not directly indicative of GPS accuracy; rather, it indicates the likelihood of the location being accurate. It is possible for DOP to indicate very low precision on a very accurate fix. Lower DOP means the GPS accuracy is likely to be higher as the potential error is lower, but a high DOP fix can still be more accurate than a low DOP fix.

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3 What are the types of DOP?

Different types of DOP measure the effect of satellite geometry on various components of your location. GDOP (Geometric DOP) is the most common, indicating the overall effect on your 3D position and time. PDOP (Position DOP) evaluates the impact on 3D position, while HDOP (Horizontal DOP) concentrates on 2D position (latitude and longitude). VDOP (Vertical DOP) is used to measure the effect on altitude, and TDOP (Time DOP) examines the influence on time synchronization.

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4 How can you find out the DOP value?

Most GPS receivers and software can display the DOP value for your location. Some of them can also show you the DOP value for each satellite or the DOP value for different types of position components. You can also use online tools or calculators to estimate the DOP value based on the satellite positions and your location. Generally, a DOP value below 2 is considered excellent, between 2 and 5 is good, between 5 and 10 is moderate, and above 10 is poor.

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5 How can you improve the DOP value?

The DOP value is determined by the satellite configuration, which changes constantly as the satellites orbit the earth. You cannot control the satellite positions, but you can improve the DOP value by choosing a location that has a clear view of the sky and avoiding obstructions that block the satellite signals, such as buildings, trees, or mountains. You can also use a GPS receiver that can track more satellites or use a differential GPS (DGPS) system that can correct the errors from other sources and reduce the effect of DOP.

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Benjamin Fostaty

Technical Support at Lotek Wireless
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Differential GPS(DGPS) is the most reliable method for creating very high precision GPS fixes. It works by having a stationary reference in the general vicinity that is subject to similar environmental factors and multipath effects. DGPS can result in fixes that have CEP of less than 1 metre.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Benjamin Fostaty

Technical Support at Lotek Wireless
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DOP can be improved by connecting to more satellites, especially when those satellites are far apart. For best results with GPS, orient the antenna or module such that the horizon is visible in multiple directions. This increases the likelihood of satellites being visible which are on opposite ends of the horizon, and therefore far apart.

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How does satellite geometry affect GPS accuracy?

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4

5

6

1 What is DOP?

2 How does DOP affect GPS accuracy?

3 What are the types of DOP?

4 How can you find out the DOP value?

5 How can you improve the DOP value?

6 Here’s what else to consider

Geographic Information Systems (GIS)

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How does satellite geometry affect GPS accuracy?

1

2

3

4

5

6

1 What is DOP?

2 How does DOP affect GPS accuracy?

3 What are the types of DOP?

4 How can you find out the DOP value?

5 How can you improve the DOP value?

6 Here’s what else to consider

Geographic Information Systems (GIS)

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