position fixing:

[bekket]

I would like to ask weather anyone has some information on the comparision of radial survey, intersection and resection.this is to do with position fixing.

[Paul Oliver]

Hi

You are talking conventional, land based navigation here. Radial Survey being map orientation and position fixing in relation to surrounding reference points.

Intersection is the location of a point by taking bearings from several other points that are quite widley seperated. Where the bearing from each point meets you get a small triangle and your location/object is there.

Resection works at sea if you are in view of the shore and can take a bearing on 3 points you can identify on your chart or map. By converting these to back bearings you can then plot the location you are at.

Hope this helps,

Paul

[Colin Barber]

I would like to ask weather anyone has some information on the comparision of radial survey, intersection and resection.this is to do with position fixing.


You ask for info. on comparison of these methods. See the first reply to your post. The method you choose depends on your needs. A two point transit will give you a line along which you are (at some point). A three point bearing (triangulation) will give you a position 'fix'. The 'fix' being within a triangle of error. A running fix will give you a position with a margin of error but you will have to account for tide and wind in doing the calculation.

The down side is all of these methods require a chart on a flat surface, reasonably dry conditions, pencil, ruler and a stable platform. Your average dive RIB provides none of these.

I suggest you stick to the GPS but always note down your outgoing track and bearing/s so that if the electronics go down you can return to somewhere close to your starting point using the reciprocal bearing/s. When travelling on reciprocal bearings out of site of land always 'aim off' a little in the uptide direction, you can always refine your course when you get in sight of your objective.

Colin