Gridded Charts Q
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Gridded Charts Q
Moderator: Tried this on the Questions forum first - may I try it here also?
I posted up the following Q recently and gratefully got a reply from, I think 'Send Clowns', here is that Q:
Q: A Northern L.C.C is overprinted with false grid. Constant of cone of chart is A. At B degrees West the grid track is C and the true track D. At which longitude is the false grid aligned?
The below is CS's reply which I found very helpful. However being dim I don't understand the part that says 'also whether E or W'. I would appreciate further information/explanation with respect to that part of the explanation and suggestions for a diagram to aid visualisation. Thanks in advance.
Ans: Comparing C and D will give you the chart convergence, and also whether E or W. On a Lamberts chart, convergence = change of longitude (from the datum) x sin of parallel of origin (or 'n' factor). Therefore, change of longitude = chart convergence/'n' That change of longitude is the difference between B and the datum.
You now have to work out which sense to apply it . In the N hemisphere, if convergence is W, B is E of the datum. In the S hemisphere, if convergence is W, B is W of the datum.
I posted up the following Q recently and gratefully got a reply from, I think 'Send Clowns', here is that Q:
Q: A Northern L.C.C is overprinted with false grid. Constant of cone of chart is A. At B degrees West the grid track is C and the true track D. At which longitude is the false grid aligned?
The below is CS's reply which I found very helpful. However being dim I don't understand the part that says 'also whether E or W'. I would appreciate further information/explanation with respect to that part of the explanation and suggestions for a diagram to aid visualisation. Thanks in advance.
Ans: Comparing C and D will give you the chart convergence, and also whether E or W. On a Lamberts chart, convergence = change of longitude (from the datum) x sin of parallel of origin (or 'n' factor). Therefore, change of longitude = chart convergence/'n' That change of longitude is the difference between B and the datum.
You now have to work out which sense to apply it . In the N hemisphere, if convergence is W, B is E of the datum. In the S hemisphere, if convergence is W, B is W of the datum.
There is a diversion of longitude if its given some latitude, on Gilberts chart. However there is a coincidence at the cos of theta, around the trans mercator, this is because hexi decimals come into play on or around the convergence zone (southern hemisphere). It can be ignored if you are bipolar.
Hope this demystifies the theory.
Hope this demystifies the theory.
Love your work!
