[GRASS-dev] Re: [GRASS GIS] #1161: g.region and r.info decimel issue when using grass python libs

GRASS GIS trac at osgeo.org
Sun Oct 3 18:37:36 EDT 2010


#1161: g.region and r.info decimel issue when using grass python libs
-------------------------+--------------------------------------------------
  Reporter:  isaacullah  |       Owner:  grass-dev@…              
      Type:  defect      |      Status:  closed                   
  Priority:  normal      |   Milestone:  6.4.1                    
 Component:  Python      |     Version:  6.4.0                    
Resolution:  invalid     |    Keywords:                           
  Platform:  All         |         Cpu:  All                      
-------------------------+--------------------------------------------------

Comment(by hamish):

 Replying to [comment:6 glynn]:
 > Given that coordinates are limited by the circumference of the earth,
 > both %.15g and %.8f should be converted without loss (i.e. adjacent
 > values should have distinct floating-point representations), so if
 > you format as decimal with the correct number of digits, you should
 > get the original value. This has to be done when you convert to decimal,
 > though; you can't "tag" floating-point values with formatting options.

 note that for lat/lon you'll need to go to %.12g or so.

 I guess what I find weird is that g.region will never report with
 precision > .15g, which is exactly representable & will never saturate the
 double-prec bitspace, and so the python repr() example above is perhaps
 using %.16f internally?
 {{{
  echo 5.1 | awk '{printf("%.16f\n", $1)}'
 }}}

 ?,
 Hamish

-- 
Ticket URL: <https://trac.osgeo.org/grass/ticket/1161#comment:8>
GRASS GIS <http://grass.osgeo.org>



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