[PROJ] Unexpected conversion behaviour.

[Chris Crook]

UNCLASSIFIED

Hi PROJ people

I am looking at a conversion (EPSG:4176->EPSG:4272) which is lat/lon->lat/lon via a distortion grid.  Unexpectedly I get a different answer by adding 360 degrees to the input coordinate.

It looks like this possibility is not accounted for when testing whether the grid is applicable, so it falls back to the less accurate option.   Is that correct? And if so would it make sense to allow longitude wrapping when evaluating conversion options?

$ test_nzgd1949.sh
+ cs2cs
Rel. 8.2.1, January 1st, 2022
usage: cs2cs [-dDeEfIlrstvwW [args]]
              [[--area name_or_code] | [--bbox west_long,south_lat,east_long,north_lat]]
              [--authority {name}] [--accuracy {accuracy}] [--no-ballpark]
              [+opt[=arg] ...] [+to +opt[=arg] ...] [file ...]
+ echo -42 173
+ cs2cs EPSG:4167 EPSG:4272 -d 8
-42.00171693    172.99984072 0.00000000
+ echo -42 -187
+ cs2cs EPSG:4167 EPSG:4272 -d 8
-42.00169999    172.99986158 0.00000000

Thanks


Chris Crook  (he/him<https://www.publicservice.govt.nz/our-work/diversity-and-inclusion/pronoun-use-in-email-signatures/>)
Geodetic Scientist

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