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GINI is software that blends the raw data of GPS and inertial navigation sensors to obtain optimal GPS/INS navigation in real-time, and best estimate of trajectory (BET) in post-processing.

GINI uses a "tightly-coupled" approach to GPS/INS integration by combining the raw data of the two sensors in a single, optimal Kalman filter. The common "loosely coupled" alternative cascades two filters, one for each sensor.

The primary functions of GINI are:

Strapdown Navigation
Receiver Aiding
Satellite Orbital Computations
Kalman Filtering
Recursive Smoothing

Sensor data accepted by GINI include:

GPS pseudorange and precise carrier phase.
The raw data of a differential reference station. (Optional)
The sensed, accumulated angle change and accumulated velocity change in the moving coordinate frame of an . IMU instrument cluster.
Free baro-inertial position, velocity, and attitude of a navigation-grade INS. (Alternative to IMU data)

GINI outputs blended GPS/INS position, velocity, and attitude, as a function of time, at a navigation reference point that you specify.

Small Businesses Now Building Tightly-coupled GPS/INS Systems

It has been recognized since the dawn of GPS that tight coupling of GPS and INS sensors is highly desirable. The sensors have complementary bandwidth and error characteristics, and coupling them obtains the best advantages of both. Owing to greater synergism of elements, tightly-coupled systems are significantly more accurate, robust, jam-resistant, and less costly.

Improved system accuracy, availability, and continuity.
Superior performance in environments where GPS signals are frequently obstructed.
Reduced system cost.

Unfortunately, in the past, tightly-coupled systems were difficult to build. In the two decades after the X-Set (the first GPS navigation system and also first tightly-coupled GPS/INS) a handful of large aerospace companies succeeded in building tightly-coupled systems, but each system was one-of-a-kind. Substituting a different GPS receiver or IMU would have been as expensive as developing the original system.

The GINI author was active in GPS/INS during those two decades, helping to design the X-Set and other, similar systems. During that time, he saw industry make the same costly mistakes over and over again, but he remained convinced of the advantages of tight coupling. So, drawing on his experience, he developed and published a new concept that makes the systems vastly easier to design, assemble, test, and modify.

Next, he assembled a team to build a tightly-coupled GPS/INS prototype using the concept. The team designed, fabricated, and successfully van tested the prototype within a matter of days, demonstrating the speed with which tightly-coupled systems can be built.

Finally, he took the software element of the concept, named it GINI®, and made it available to system developers. The conference article introducing GINI was picked up and re-printed in the February 1997 issue of IEEE Aerospace and Electronics Systems Magazine.

Since then, several small and medium-sized companies have succeeded in building GPS/INS systems using GINI.

GINI Specifications.

Opportunity for Small Enterprises

The GINI vision is to bring tightly-coupled GPS/INS within reach of small enterprises serving niche markets, by making it possible for the enterprises to build their own tightly-coupled systems.

Example markets include surveying, mapping, positioning, instrumentation, exploration, resource management, remote sensing, and special-purpose navigation. Examples of special-purpose navigation include road-surface monitoring and crop-dusting.

Tightly-coupled systems were previously available for those markets, but the options were few and expensive. Loosely coupled systems were the more common choice, but that meant settling for systems that are less accurate, less robust, and more expensive.

The ability of small businesses to build their own tightly-coupled systems means that they can choose the exact sensor combination most appropriate for their own unique application. They can then change the sensors in response to developments within their specialty.

For numerous small businesses, GINI is a source of empowerment. There used to be only a very small list of companies that could build tightly-coupled systems. Now, your small enterprise might be a candidate to join the list.

Advantages

Simple. GINI bundles up complexity, and gets it out of your way. That leaves you to specify your system at a high level, acquire sensor data, and manage the timing of sensor events. In other words, you can focus on what your system is supposed to be doing, instead of on the inner workings of GPS/INS integration.

Flexible. The central ideas that led to GINI began as a way of easing the complexity and inflexibility of prior GPS/INS designs. The first conference paper on GINI was entitled: "Achieving Modularity with Tightly-Coupled GPS/INS." It is relatively easy to modify a system built with GINI by substituting other sensors. The same software works in real-time as in post-processing.

Accurate. In addition to flexibility, applicability, and ease of use, GINI achieves accuracy by optimizing uniquely for each IMU. That is especially important for low-cost IMUs where the peculiarities of each device have to be taken into account. A high-fidelity modeling approach is used; It was not known at GINI design time which parts of the modeling would be especially critical to eventual applications, and so the best modeling was applied all across the board.

Compact and Fast. In a typical application, GINI requires 0.2 Megabytes of memory, and runs in a small fraction of the computing capacity of a desktop PC. It can post-process hours of recorded field data in a few minutes.

Portable. GINI is written in a generic subset of C, making it portable. GINI is equally at home in a workstation, PC, or deeply embedded in a real-time system. (+) GINI reference to functions outside itself are resolved through a module that can be adapted to your system.

Drawbacks

The GINI concept is not a panacea. Conference articles address the drawbacks. GINI is not guaranteed to work in every application. There are requirements placed on sensors to be compatible, and while those requirements are easy to satisfy, they cannot be dismissed.

GINI leaves the choice of sensors and features up to system developers. Hence, it cannot shield developers from having to understand the sensors' basic properties and limitations. Developers do not need anything like the knowledge required when designing a GPS receiver, IMU, or navigation filter. But complete newcomers to GPS/INS are not advised to use GINI as the starting point for learning.

The developer will need access to systems integration capability, and will have to do prototyping work to find out if the software is right for a particular application. The toughest single task is to tag inertial data with GPS time, accurate to a small fraction of a millisecond. Next in order of difficulty is data acquisition. The developer will have to be able to sort through the options regarding GPS augmentation and be able to interface with sensor manufacturers. Even if you just simply have a file of data to post-process, it will still be necessary to ascertain what that data represents.

Building a tightly-coupled GPS/INS requires up-front investment to purchase sensors for the prototype.

Support

Most GINI users require support. You get individualized attention from the GINI author, owner of the business, and someone who is knowledgeable and genuinely interested. (*)

"Your level of support has been astonishing."

(*) This is not a commitment to accept an assignment, nor to provide labor, without a written quote from Knight Systems describing the work to be done, and estimating its cost. Don's availability varies, and is not guaranteed. Applications involving software modification or incidental work may or may not be feasible, due to limitations of time, or of the software, or both.
(+) Embedding in non-Intel microprocessors may or may not be feasible, depending on the availability of tools for software conversion, and on the availability of time to complete the conversion.

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