[GRASS-dev] [GRASS GIS] #3480: m.cogo enhancement request: add declination support

GRASS GIS trac at osgeo.org
Sun Jan 21 11:44:31 PST 2018

#3480: m.cogo enhancement request: add declination support
 Reporter:  fgfletcher   |      Owner:  grass-dev@…
     Type:  enhancement  |     Status:  new
 Priority:  normal       |  Milestone:
Component:  Default      |    Version:  7.0.1
 Keywords:  m.cogo       |        CPU:  Unspecified
 Platform:  MacOSX       |
 m.cogo converts  a sequence of (bearing,distance) pairs into cumulated
 cartesian (x,y) coordinates beginning from a user provided starting x,y

 The bearing entry is in the form "N 52:17:04 W", widely used in survey

 However, many surveys use magnetic bearings which are rotated from true
 geographic North by an angle called the Declination - which itself depends
 on the date and survey location.

 Currently when using m.cogo with such data it is first necessary to
 convert the magnetic bearing by adding(subtracting) the Declination as
 known for the date and location of the survey.

 This is tedious and error prone when a survey could consist of hundreds of
 bearings, especially as adding a declination can "wrap around" a bearing
 into a different quadrant, for example: a 15° declination wrapping  from N
 10 E to N 5 W.

 It would be very helpful if one could provide a Declination argument to
 m.cogo which would be added to each bearing.  All that is needed in
 processing is to add the Declination value to the Azimuth (from input
 bearing) and handle the special cases of result <0 or >= 360.

 Way above my skill level, but I'm hoping somebody might take an interest.

Ticket URL: <https://trac.osgeo.org/grass/ticket/3480>
GRASS GIS <https://grass.osgeo.org>

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