NAVIGATION, COMMUNICATIONS & POSITIONING Navigation software alert to errors, disagreements, malfunctions

Tony Woods Cochrane Technologies Typical C-NAV software display showing a drilling unit after positioning it on location. Software packages are sometimes quirky, error prone, and subject to sudden, unexplained failure that often results in long periods of down time and loss of productivity. Many require numerous operational parameters to be entered by the operator at the time of initialization.

Jul 1st, 1995

Tony Woods
Cochrane Technologies

Software packages are sometimes quirky, error prone, and subject to sudden, unexplained failure that often results in long periods of down time and loss of productivity. Many require numerous operational parameters to be entered by the operator at the time of initialization.

Cochrane Technology's solution to these problems was to write their own software for C-NAV, a DOS-based survey and navigation application for the marine industry. The software is stable and virtually crash-proof. Any peripheral error that occurs is displayed and logged but does not lock the system out. The core functions remain in operation continuously, even though reduced capabilities are in effect. Operators are allowed to correct a problem while remaining on-line and the system will automatically recognize when the problem is fixed.

This allows the job to continue and minimizes down time.

Also, all survey parameters are stored when they are entered or changed so that if a power failure occurs these values are automatically recalled. The system can be back on-line in about 30 seconds from the time power is restored.

Displays are redrawn to the screen at a rate of about 4,000 times per second. All port input and output routines are independent of the normal program loop, thereby allowing a multitude of different equipment combinations to be incorporated. The software can handle up to 18 serial I/O ports, two bi-directional parallel ports, and multiple analog to digital interfaces. All data is logged real-time for archiving purposes.

Tracking remote vessels

CNAV also incorporates an efficient method of tracking remote vessel locations. Remote vessels are outfitted with GPS receivers which are fed differential RTCM-104 messages locally from the main vessel. Then the output of these remotes are time delayed based on the phenomenal GPS timing signals to provide a continuous data stream to the main vessel using point to multi-point, spread spectrum radio/modems at 64 Kbps.

Since each remote broadcast is offset from each other in time, there is no need to poll them and thereby increase processing overhead. All remote vessels as well as the main vessel are updated on the CNAV display every second. This gives a real-time view of vessel activity that is similar to an air traffic controller's display.

C-NAV also provides the ability to display and obtain bearing and range information from cartographic information. This data can be imported from various CAD systems in the Data Exchange Format (DXF). Cartographic information can also be entered using a text editor of choice to define multiple entities, colors, and display characteristics.

Additionally, waypoint information can be stored in text format and displayed graphically on screen. Both range and bearing to the waypoints from any other object can be obtained at a glance.

Two forms of cursors are incorporated to allow the ability to measure distances and bearings quickly and easily. One of these cursors is controlled from the keyboard, and the other from the mouse/trackball.

Another unique feature of this software is the ability to define the main vessel's shape and size. Virtually any shape can be defined, but is limited to 100 points. These vessel shapes also provide up to 12 anchor locations and unlimited pre-defined antenna offset points.

Users can also input antenna offsets on the fly during survey operations. Provisions are also made for derrick barge operations to show the position and orientation of the crane. When a remote vessel package is placed on the end of the crane boom, the software will rotate the crane's position and even account for inclination of the boom itself. This feature is extremely useful when positioning a template or during jacket installation.

Pre-defined survey track lines are easily entered and displayed. Three different line styles are available for use. Single lines are defined by two points, multi-point lines can be used as a predefined route, and curved lines are normally used to represent pipeline proposed locations.

Storage format

On line data can be stored in two formats. The first is the event format which only logs data at the predefined interval and the "all" format logs data every second. Eventing basis can be derived from time or distance.

No operator input is required to go on-line or off-line, and the software even changes from increasing to decreasing automatically. Distance downline, off-line (cross track error), to the end of the line, and to the next event can be displayed as well as a left/right indicator to help captains stay on-line. These "on-line" abilities are not limited to the main vessel, any remote vessel can be directed and data collected in the same manner.

During pipeline laying operations, special anchor templates can be generated and displayed during transit prior to arriving on location to help determine the most optimum anchor spread. These templates can then be placed on screen to be used as a guide to help place the anchors.

X/Y location, as well as range and bearing to the anchors, is displayed to give anchor windlass operators the information they require immediately. The fairlead distance and bearing is calculated to the fairlead, not the antenna location. Anchors can be dropped from the main vessel, at an X/Y location, at a range and bearing from the fairlead, or from a remote vessel. When an anchor is dropped, the software automatically stores the location in a separate anchor file that is then treated as a waypoint. Therefore, range and bearing information is available to and from all other objects.

Input from two navigation systems can be displayed on screen simultaneously for comparison and quality assurance purposes. Datum transformation from WGS-84 (GPS) to a user defined datum is performed real-time.

Cochrane will offer a version of the package in the near future. They are also planning the release of a Windows version soon after the release of Windows 95.

AUTHOR:
Tony Woods is the special projects manager for Cochrane Technologies, a Lafayette, Louisiana (USA) based navigation and positioning software development firm.

Copyright 1995 Offshore. All Rights Reserved.

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