voyage leg analysis (1 Viewer)

Good afternoon,

I have track data (position: latitude, longitude and date, time speed and fuel consumption) for a fleet of ships and I’d like to analyze it by leg.

Legs are voyage segments between waypoints. I have a table of 150 waypoints – name, latitude, longitude

How can I process the track data to give leg analysis results such as

Elapsed time (finish time – start time)
Fuel consumed
Average speed

With MS Access?

The tables are relatively large, but I’ve provided excerpts to describe what I’m working with.

I don’t have much experience with Access, so any help is much appreciated!

Regards,
Dave

TVehLegs table :
VehID
Leg
Latitude
Longitude
DateTime
FuelAmt
Mileage
Driver

Implicit in this is that you have Lat/Lon coordinates but need linear-distance formulas to determine the length of the leg. Do you already have formulas for that computation? Or do you have other ways to compute the linear distance between two related waypoints?

Such formulas exist, but you have to be careful about how you use them. What are the distances involved here? 1, 10, 100, 1000 miles?

To compute the linear distance, you can use something called the "Great Circle Distance" formula, which should be possible to look up online. You give it lat/lon for starting and ending points and you have to feed it a couple of constants for whether you are doing miles or kilometers, but it gives you the distance in a way that would be usable for the analysis you appear to be attempting.

For very short distances, you can pick a latitude or longitude or both (depending on whether you would want to precompute the x/y values corresponding to your lat/lon values). Whether you pick a central latitude, a central longitude, or a central coordinate depends on whether you would then try a Mercator projection, Lambert projection, or Cassini-Soldner projection to do the pre-conversion. IF you are talking really long legs between waypoints, you might be unable to use the pre-conversion method because the accuracy of pre-conversion drops off REALLY fast after a few hundred miles. Fast enough to become unusable for pre-conversion.

Be careful when dealing with ships and the way they navigate.
Most of the time they will be using rhumb line instead of great circle since great circle is a major pain in the a.. to use.
For short distances (<100 nm) there will be not appreciable difference between the two distances but a transatlantic voyage will give you a good difference.

Even if a ship is claiming to use a great circle, they will most likely be using rhumb line between points on the great circle.
The problem is the course to steer will continously change on a great circle while a rhumb line will give you a steady course.

You cna find a good illustration of the difference on this page: https://www.dougv.com/2009/07/calcu...en-two-latitude-longitude-coordinates-in-php/