Dear LLH,
No problem to wait your trimming for precise formula. If you have such one which is also convenient to apply, I would like to use it.
There are other formulae (precise?) in literatures. Here is the one I met in Gernold North’s book:
I do not use GN’s approach for two reasons:
1. His listed formulae look sophisticated and do not convince me by tests through examples, just theory.
2. In visual measurements without equipment aids, a person often produces human error which already overrides the need of trimming for “precise” mathematics.
I am speaking as a practical amateur. Try to measure repeatedly the same lunar photograph, you probably get pixel reading of 80 today, 78 tomorrow or 82 next week. The worst uncertainty of measurement comes from short shadow such as the Straight Wall I showed in my worked example: you probably get unsteady readings of 15, 16, 17 or even 18 pixels !!! More uncertainty if you measured eccentric craters such as Schiller in the SW limb. |
發表於 2008-4-9 02:27:17