MINESAPINT2
Member
Is it possible to convert Decca co ordinates Chain 3B to Lat Long WGS84 and vice versa? Perhaps something available online?
Thanks
Mike
Thanks
Mike
It cannot be done with any accuracy! I used to have a shipmate Decca and a 2000D, we used the kingfisher charts for wreck fishing, the problem is, Decca wanders at different times of the day, you could be bang on a wreck at 12 noon, but 300yards away at 4pm, we tested this using GPS with differential, decca could easily be 400 yds out of position at different times of the day, forget it, it will drive you daft!Is it possible to convert Decca co ordinates Chain 3B to Lat Long WGS84 and vice versa? Perhaps something available online?
Thanks
Mike
Decca receivers used to mange it with 'reasonable' accuracy using 1970s logic ICs, so it cannot have been that hard by modern standards.Is it possible to convert Decca co ordinates Chain 3B to Lat Long WGS84 and vice versa? Perhaps something available online?
Thanks
Mike
Is it possible to convert Decca co ordinates Chain 3B to Lat Long WGS84 and vice versa? Perhaps something available online?
Thanks
Mike
I am intrigued as to why you want to do that. Please spill the beans.Is it possible to convert Decca co ordinates Chain 3B to Lat Long WGS84 and vice versa? Perhaps something available online?
Thanks
Mike
It cannot be done with any accuracy! I used to have a shipmate Decca and a 2000D, we used the kingfisher charts for wreck fishing, the problem is, Decca wanders at different times of the day, you could be bang on a wreck at 12 noon, but 300yards away at 4pm, we tested this using GPS with differential, decca could easily be 400 yds out of position at different times of the day, forget it, it will drive you daft!
Yes, it reminded me of the days of listening to radio Caroline, the signal would fade in and out, in the evening, but as Wing Mark said, the repeatability of decca could be quite good, but only at the same time, ie, if you drop gill nets at noon, you will find them again at noon, but not at 9pm, local fishermen would calibrate the decca from a known buoy before setting out.I seem to remember it was particularly inaccurate around sunrise and sunset, due to diffraction (or refraction?) of the radio signals.
Now that is interesting. It would have been useful to know when I was teaching electronic nav aids to MN officers. However, for mariners working at sea level the Decca errors were mainly due to differences in the speed of propagation over land and sea. I suspect that at the heights aircraft were flying these errors were negligible.People seem all too eager to knock Decca for accuracy but a whole generations of pilots used it on the N Sea for navigation and instrument approaches, one of my bases had a Decca approach with, unless I am badly mistaken, a MDH (minimum descent height) of just 350ft, exceedingly low for a non-precision approach. That could not be possible without considerable confidence in its accuray and reliability.
Is it possible to convert Decca co ordinates Chain 3B to Lat Long WGS84 and vice versa? Perhaps something available online?
The principles aren't difficult; if you know the location of the transmitters you can work out the theoretical positions without over much difficulty; it's a conventional hyperbolic navigation system. Decca "lanes" are simply lines of equal difference of radio path length from two transmitters. The problem arises because there are a lot of secondary effects that vary with position and time, and which can't be dealt with by an algorithm; someone has to go and measure them.I doubt there are many, if any, people left who know the details of the Decca system sufficiently well to know how to do it. My dad was chief surveyor at Decca & this was his stuff, but he's travelling the Decca lanes in the sky now having reached an age of 94. There were no former colleagues at his funeral; he outlived them all.
And I'm trying desperately to remember the global system we tried to use in 1986 in Svalbard. Not Transit; it wasn't satellite based. Precision was good - about 100m - but accuracy was in the kilometre range!
We used Decca to lat/long conversions on our airborne nav computers in the 1970's and they were probably significantly more accurate than the charts. However, the caveats on reduced repeatability at dawn and dusk of course still applied! However, on one system we had an algorithm that predicted the real-time accuracy of the conversion (in metres), taking into account geometry and daily and seasonal fluctuations.By algorithm? I doubt it.
No; it was something else. It'll come back to me. Its advantage was global coverage; I don't think it was very widely used.Loran?
And why (OP) does anyone want to convert Decca to lat long? There are no Decca signals!
Consol? We tried in in the Channel in '63. Counting dots on long wave to get a bearing from the station in Norway (?) Not very precise..No; it was something else. It'll come back to me. Its advantage was global coverage; I don't think it was very widely used.