Commits on Feb 1, 2024

1. Add +proj=mod_krovak projection method for Modified Krovak that appli… …

   …es to S-JTSK/05 in the Czech Republic
   
   Validated with the test point given in EPSG Guidance Note 7-2
   
   Also validated with CUZK online calculator at https://geoportal.cuzk.cz/(S(g4ipaut0ckzb5lellu153lvf))/Default.aspx?head_tab=sekce-01-gp&mode=TextMeta&text=wcts&menu=19
   
   Unfortunately this calculator does not offer 'elementary'
   transformations, and cannot just validate Modified Krovak alone.
   The best we can do is to use ETRS89 <--> S-JTSK/05 / Krovak modified,
   which involves a Helmert transformation as well for the datum
   transformation.
   
   * Validation of reverse modified Krovak:
   
     Online calculator:
     - Souřadnice/input: -5568990.91 -6050538.71 100
     - Source CRS: S-JTSK/05 + Bpv (-Y-XH /east-north)
     - Destination CRS: ETRS89 (BLh / DEG)
     - Výsledek/result: 50.208297081 16.848326835 143.762
   
     With PROJ:
     echo -5568990.91 -6050538.71 100 | bin/cs2cs -d 9 EPSG:5516 EPSG:4937 --3d
     50.208297081 16.848326833 143.143233569
   
     Note the different on longitude is totally neglectable: 0.1 mm, as computed by:
   
     $ echo 50.208297081 16.848326835 50.208297081 16.848326833 | bin/geod -F "%.4f" -I +ellps=GRS80
     -90d 90d 0.0001
   
     and that when outputing Krovak modified, the online calculator displays Y/X with
     a precision of 1 cm.
   
     The difference on Z is significant, but can be explained from the fact that
     the online calculator using Baltic Height for S-JTSK/05 and thus apply a
     Baltic Height<-->ETRS89 geoid that we don't apply here.
   
   * Validation of forward Krovak using same point:
   
     Online calculator:
     - Souřadnice/input: 50.208297081 16.848326835 143.762
     - Source: ETRS89 (BLh / DEG)
     - Destination: S-JTSK/05 + Bpv (-Y-XH /east-north)
     - Výsledek/result: -5568990.91 -6050538.71 100
   
     With PROJ:
     $ echo 50.208297081 16.848326835 143.762 | bin/cs2cs -d 2 EPSG:4937 EPSG:5516 --3d
     -5568990.91 -6050538.71 100.62

   

   rouault committed Feb 1, 2024
   Configuration menu

   • View commit details
   • Copy full SHA for 828a472
   • Browse repository at this point

   Copy the full SHA

   828a472 View commit details

   Browse the repository at this point in the history