snap/height_ref_notes.txt at master · linz/snap · GitHub

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* Coordinate file can contain geoid info
* Coordinate system can include height reference surface
* Explicit geoid info overrides height reference surface
  (snap warning if both present)
  (? option in snap to recalculate on load, or warn if different?)
* CSV coordinate file, needs to identify explicit geoid info and also
  default height type for network (less critical as not output from
  CSV?)

* snapconv can change coordinate system to coordinate system with
  height reference.  What will this do to geoid info?

* snapgeoid can
  * add explicit geoid info from height ref sys or geoid file
  * remove explicit geoid information
  * update geoid information from coordinate system if it defines geoid
  * add/remove height reference system to coordinate system

* snapconv and snapgeoid will both update orthometric heights if
  converting between coordinate systems with height reference
  surfaces there is no geoid information.

* snapconv and snapgeoid will maintain ellipsoidal heights when
  adding or removing either type of height.  Height type will revert
  to ellipsoidal.

* Can force retention of orthometric heights in either program.
  Will set height type to orthometric

* If adding geoid info to coordinate file without it, then will retain
  coordinates according to type defined in coordinate file. Default
  is ellipsoidal.

============================================================

Network has two flags to support this

NW_EXPLICIT_GEOID, meaning the geoid info is set for each station and
   independent of the coordinate system

NW_ELLIPSOIDAL_HEIGHTS, meaning input/output heights are ellipsoidal

============================================================

Functions

network_has_explicit_geoid
network_set_explicit_geoid 1/0
network_set_station_geoid_info
    option to preserve orthometric height
    specific station, sets explicit geoid
network_update_geoid_info_from_height_ref
    flag which height type to preserve
    flag to remove explicit geoid info, which also
    sets info to zero where cannot be calculated

network_set_height_type_ellipsoidal
network_set_height_type_orthometric

network_update

=============================================================

snapconv/snapgeoid options relating to heights

-l  list coordinate systems
-r  list height reference surfaces

-h hrs      set geoid info from height ref surface
-g geoid    set geoid info from geoid file
-c          set geoid info from coordinate sys
-z          remove (zero) explicit geoid info
-k          keep existing explicit geoid info - only calculate if not already defined

-a hrs      add height ref surface to coordinate system
-d          drop height ref surface from coordinate system

-e  set height type ellipsoidal
-o  set height type orthometric

-p  set height type orthometric and keep orthometric heights fixed in conversions

-i  ignore errors calculating specific geoid heights. Geoid info not changed

-y  conversion epoch
-q  quiet mode