NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: typical standard deviation?
From: M v Noorden
Date: 2009 Aug 13, 02:07 -0700
From: M v Noorden
Date: 2009 Aug 13, 02:07 -0700
>EXCELLENT! I am afraid that with so few people such as myself out here who actually practice celnav, our hopes for at sea data are fairly slim, especially from the larger vessels. >I wouldn't expect to find such data. During the history of celestial navigation _IT_ was the most accurate navigation system available so there was no other data that the celnav positions could have been compared with to develop such an accuracy data set. Really, only since the development of GPS (maybe LORAN C) has such another set of positions become available so only now can such data be developed. But how many navigators continued to use celnav on a regular basis and then logged the accuracy of the celnav position derived after comparison with the contemporary GPS positions and then made their logs available. Acually you don't need an exact GPS nor a hugh amount of people to estimate the error. A good way of doing the analysis would be to use what is called a 'MSA' (Measurement System Analysis) and is used in industry to distinguish between operator errors and machine errors. A simple setup would involve one sextant, one ship and 2 or 3 operators. The operators (users) will shoot in random orders with the same instrument and calculate their position. The total variance (square of the standard deviation) is the sum of the variance of the inter operator error and the error caused by the measurement setup. If you want to include all types of potential errors due to for instance horizon (as mentioned above), you can either instruct the operators very well (the error will be in the test setup) or not at all (the error will be in the operator part). If the experiment is carried out at the same location, no GPS fix is needed or desired, it will add an extra variance to the equation (but probably very small) If somebody is willing to carry out this experiment, I am more than happy to assist with the statistical part. Regards, Maarten van Noorden --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---