engineering

GPS/INS

GPS/INS is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand GPS/INS rather than just read about it. In short: GPS/INS is the use of Global Positioning System (GPS) satellite signals to correct or calibrate a solution from an inertial navigation system (INS). The method is applicable for any global navigation satellite system (GNSS)/INS system.

Key takeaways

GPS/INS belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect GPS/INS to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GPS/INS from memory before moving on to harder problems.

Reference excerpt

GPS/INS is the use of Global Positioning System (GPS) satellite signals to correct or calibrate a solution from an inertial navigation system (INS). The method is applicable for any global navigation satellite system (GNSS)/INS system.

Overview

GPS/INS method The GPS gives an absolute drift-free position value that can be used to reset the INS solution or can be blended with it by use of a mathematical algorithm, such as a Kalman filter. The angular orientation of the unit can be inferred from the series of position updates from the GPS. The change in the error in position relative to the GPS can be used to estimate the unknown angle error. The benefits of using GPS with an INS are that the INS may be calibrated by the GPS signals and that the INS can provide position and angle updates at a quicker rate than GPS. For high dynamic vehicles, such as missiles and aircraft, INS fills in the gaps between GPS positions. Additionally, GPS may lose its signal and the INS can continue to compute the position and angle during the period of lost GPS signal. The two systems are complementary and are often employed together.

Applications GPS/INS is commonly used on aircraft for navigation purposes. Using GPS/INS allows for smoother position and velocity estimates that can be provided at a sampling rate faster than the GPS receiver. This also allows for accurate estimation of the aircraft attitude (roll, pitch, and yaw) angles. In general, GPS/INS sensor fusion is a nonlinear filtering problem, which is commonly approached using the extended Kalman filter (EKF) or the unscented Kalman filter (UKF). The use of these two filters for GPS/INS has been compared in various sources, including a detailed sensitivity analysis. The EKF uses an analytical linearization approach using Jacobian matrices to linearize the system, while the UKF uses a statistical linearization approach called the unscented transform which uses a set of deterministically selected points to handle the nonlinearity. The UKF requires the calculation of a matrix square root of the state error covariance matrix, which is used to determine the spread of the sigma points for the unscented transform. There are various ways to calculate the matrix square root, which have been presented and compared within GPS/INS application. From this work it is recommended to use the Cholesky decomposition method. In addition to aircraft applications, GPS/INS has also been studied for automobile applications such as autonomous navigation, vehicle dynamics control, or sideslip, roll, and tire cornering stiffness estimation. Integrating inertial navigation systems with high-precision GNSS technologies, such as real-time kinematic (RTK) and precise point positioning (PPP), enhances the accuracy of autonomous vehicle navigation by providing high-precision localization.

Worked examples

Example 1 — a first encounter with GPS/INS

Start with the simplest possible case. Write down what GPS/INS claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to GPS/INS before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about GPS/INS ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of GPS/INS

In research: GPS/INS appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses GPS/INS in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: GPS/INS is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aerospace engineering, Inertial navigation, Navigation, so understanding it makes those chapters shorter.
In everyday life: Look for GPS/INS outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study GPS/INS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GPS/INS means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain GPS/INS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GPS/INS in simple terms?

Why does GPS/INS matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study GPS/INS?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on GPS/INS.