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Could a checker be made for GC41X9F Explorer 221 Challenge?

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A challenge cache asking the qualifying cacher to find geocaches in 221 squares of the Ordnance Survey 221 map. The CO made a macro to check this but it will not work on my computer. Thanks

asked Apr 9, 2016 in (OBSOLETE) Checker requests by dannyphipps (120 points)
It should be possible to do this using http://project-gc.com/Challenges/GC4Y6PT/19407?edit&tagId=19456 as the other "Explorer Challenges" already have.
There is discussion about these caches. It is no TODO list: http://forum.project-gc.com/viewtopic.php?f=10&t=74
I have made 250 & 209 , the next one is 157 which i'm working on at the moment.. Yours I will do after that. The json file I expect to have ready by the end of next week.

1 Answer

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The checker is released the link is

http://project-gc.com/Challenges/GC41X9F/19486

answered Apr 15, 2016 by vogelbird (Expert) (48,120 points)
There might be a problem CHOCALCHEMY has a ok result created by the CO  with the GSAK macro but fails with only 213 of 221 squares.

the problem might be that straight lines between point in WGS84 is not the same as lines in BNG.
There was a discussion of a similar problem about another checker.
If the a straight NS EW line has the same coordinares unchanges in booth systems the checker sould work. If they are not then the checker has to be done in BNG
Each 1x1 klik is converted so there is a very small margin of error between those points and I cannot compaire the GSAK result.

The TOP25 in the Netherlands is also based on this methode and after consulting the CO the margin of error was acceptable with the only difference with the UK that the squares are 2.5x2.5 kliks. (so the error in the Netherlands is bigger)

I send the CO of the Explorer250 and Explorer157 the link of those checkers but received no reaction so far.

The conversion of the point takes a lot of time and I would like to know if the slight margin of error is acceptable for the British CO's before continuing with the other Explorer challenges.
The CO of the Explorer157 challenge has responded that it is sufficiently accurate and has added a link to it on his cache page.
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