Chart Projection


Furuno Fan
Is there an easy way to see what chart projection has been used for the specific area the NN3D is using to navigate at the time? Mercator, etc...

And am I right that all charts are now to WGS84?

Thank you.

To help potential replies (!) it's important to know the projections for two main reasons,

1) To know if your chart datum is set correctly
2) You know if you need to set your route planning to Great Circle or Rhumb Line tracking.

Both can make a significant difference.

Does anyone know?

Hi Johnny,

Thanks for this. Do you also know how I establish if the specific chart I am using at the time is a Mercator projection (requires the nn3d to be set to rhumb line tracking) or a Gnomic projection (requires the nn3d to be set to great circle tracking)?

MM3 charts use a Mercator projection. Mercator is the most common projection used in maritime navigation; primarily because rhumb lines plot as straight lines.
Hi Johnny, thanks for the reply. My question was that for long distances across, for example, the Atlantic, one would expect gnomic charts and therefore great circle nav (which is possible in nn3d). Shall I ask my supplier? All my charts are Admiralty raster. Piers
The NN3D/TZtouch like MaxSea TZ uses Mercator projection style charts.
Maybe this from the MaxSea Manual will clear your question.

MaxSea Time Zero is capable of displaying great circle or rhumb line routes. The greatcircle route is the shortest path between two points on a sphere, like the Earth. A rhumb line route crosses all meridians of longitude at the same angle. Since the charts
displayed by MaxSea Time Zero are Mercator projections, rhumb line routes appear as
straight lines and great-circle routes appear as curved lines.

Additionally, I found the NN3D manual states on the specification sheet that it is indeed Mercator projection. Here is a quote from the manual about the great circle setting.

The two methods to measure the course distances are great circle and Rhumb line.
Great circle is the shortest line that joins two points on the surface of the earth. Rhumb line is a straight line compass course between two points. The great circle path is short, but requires frequent heading changes.

The NN3D will base the route on either method (based on your chosen setting) but the chart itself is Mercator projection.
Thanks Johnny. I understand the difference between rhumb line and great circle (I used to teach navigation!), but what I take from here is that all charts used in the nn3d are Mercator projections. BTW, I am told by my supplier that I don't have MaxSea, I just use the embedded nn3d s/w with Admiralty raster charts.

Best regards - Piers