[GRASS-dev] [GRASS GIS] #2918: Infinite loop in i.landsat.toar with method=DOS4

[GRASS GIS]

#2918: Infinite loop in i.landsat.toar with method=DOS4
----------------------------+-------------------------
  Reporter:  DmitryKolesov  |      Owner:  grass-dev@…
      Type:  defect         |     Status:  new
  Priority:  normal         |  Milestone:  7.0.4
 Component:  Imagery        |    Version:  unspecified
Resolution:                 |   Keywords:
       CPU:  Unspecified    |   Platform:  All
----------------------------+-------------------------

Comment (by mlennert):

 Replying to [ticket:2918 DmitryKolesov]:
 > == Description: ==
 > I.landsat.toar with method=DOS4 fails to stop. For example if run the
 module using Landsat8 scene (id=LC81680222013351LGN00) as input, the
 module doesn't finish the calculation.

 Thank you for the very detailed description and the nice catch !

 [...]

 > == Proposed solution: ==
 > I see two possibilities if Tz becomes NaN:
 >  * emit fatal-error like "DOS4 method isn't applicable for the scene.
 Use other method or use other sun_elevation parameter." and exit.
 >  * emit warning, then reset Tz and Tv, using default values (1.0) for
 the coefficients
 (http://trac.osgeo.org/grass/browser/grass/branches/releasebranch_7_0/imagery/i.landsat.toar/landsat.c#L122).
 >

 I'm no expert in the different DOS versions, but DOS4 is defined as:

 DOS4: TAUv = exp[-t/cos(sat_zenith)], TAUz = exp[-t/sin(e)], Esky = PI *
 radiance_dark

 Does this really make sens when TAUv and TAUz are set to 1 ?

 Unless it does, I would prefer your first solution.

--
Ticket URL: <http://trac.osgeo.org/grass/ticket/2918#comment:1>
GRASS GIS <https://grass.osgeo.org>