

Feedback requested on an idea to simplify entering locations on GPS devices - jgrahamc
http://www.jgc.org/blog/2006/07/simple-code-for-entering-latitude-and.html

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cperciva
I have four suggestions for improvements:

1\. Remove L from your alphabet. As long as people use upper-case letters,
it's fine; but someone is going to use lower-case letters and get confused
between "l" and "1".

2\. Remove T from your alphabet. With poor handwriting, "T" and "7" can be
confused.

3\. Remove U from your alphabet. It's easy to confuse "U" and "V".

(Note that 29^9 > 6.48 x 10^12, so the above changes don't affect the ability
to pack the value into 9 symbols.)

4\. Use a better checksum. Maybe there's some deep logic which I'm missing,
but I can't see any way to prove that your checksum will detect all single-
symbol errors or all two-symbol swaps (these are by far the two most common
data-entry errors). I suggest using C = 1 x p_1 + 2 x p_2 + ... + 9 x p_9 mod
29, which will always detect both of these errors.

\-- the other local Comlab DPhil.

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jgrahamc
Thanks for the feedback. I'll look into implementing those changes. I'm not
sure why I chose that particular checksum... it's been a while since I wrote
this.

John.

