[GRASS-dev] Re: [GRASS GIS] #1562: Introduction of spatial and temporal vertical units for raster3d maps and r3.support

GRASS GIS trac at osgeo.org
Mon Feb 6 14:37:52 EST 2012


#1562: Introduction of spatial and temporal vertical units for raster3d maps and
r3.support
--------------------------+-------------------------------------------------
  Reporter:  huhabla      |       Owner:  huhabla    
      Type:  enhancement  |      Status:  closed     
  Priority:  major        |   Milestone:  7.0.0      
 Component:  Raster3D     |     Version:  svn-trunk  
Resolution:  fixed        |    Keywords:  r3.support 
  Platform:  Unspecified  |         Cpu:  Unspecified
--------------------------+-------------------------------------------------

Comment(by huhabla):

 Replying to [comment:11 cmbarton]:
 [snip]
 >
 > This example seems to do what I would need a temporal GIS to do. It
 suggests that handling negative numbers is not a problem. So perhaps we
 are talking past each other somewhat.
 >
 > A calendar date (e.g., 6 February 2012) is in fact a relative date
 calculated from an arbitrary moment in the past. However, I suppose that
 program date functions treat this differently than what you are calling
 "relative dates". For most prehistoric/deep time analyses--archaeological
 and paleoenvironmental--the kind of relative date that you show above
 should serve fine.


 I use the absolute and relative time definition of the GRASS datetime
 library which is a common concept in temporal GIS:
 1) Absolute DateTimes express a single time or date referenced to the
 Gregorian calendar (e.g. 14 Feb 1995) [1]
 2) Relative DateTimes express a difference or length of time (e.g., 201
 days 6 hours) [1]

 [1] http://skagit.meas.ncsu.edu/~helena/gmslab/htdoc/time/index.html


 >
 > In fact, while these are written as a text string (e.g., AD 1235 or 3150
 +/- 200 cal BC), using them in a temporal GIS would be much easier if they
 were just transformed into numbers (e.g., +1235 and -3150).
 >
 > This example brings up another issue that may be worth thinking about at
 some point. Many age estimates in the deep past are expressed with some
 kind of error range (often a mean +/- 1SD or 2SD). Often readers
 (including archaeologists) just focus on the mean. But actually, a
 calibrated radiocarbon date of  3150 +/- 200 cal BC means that the dated
 material has a 65% chance of falling between 3350-2950 BC. This can be
 very important when comparing different events. It would be worth thinking
 about how to express such uncertainty or at least date ranges rather than
 a single date in a temporal GIS so that comparisons between events with
 overlapping ranges would be considered as contemporaneous (or even better
 contemporaneous within some probability).

 The temporal GIS framework allows the use of interval time. You can add
 relative or absolute time intervals to raster, raster3d and vector maps
 and register them in space time datasets. Hence maps with overlapping time
 intervals are supported in space time datasets. These intervals may
 represent the uncertainty?
 The temporal relations between the registered maps can be computed using
 t.topology[1]. It is possible to sample space time datasets with each
 other[2].

 [1]
 https://trac.osgeo.org/grass/browser/grass/trunk/temporal/t.topology/test.t.topology.reltime.sh

 [2]
 https://trac.osgeo.org/grass/browser/grass/trunk/temporal/t.sample/test.t.sample.sh


 > The thing is, the concept of actually implementing a production-level
 temporal GIS is very exciting and offers a the potential for new kinds of
 analyses that have never before been possible.

 I hope that the temporal GIS framework will be very useful indeed.

 Sorry for undocumented modules and tests, but i need first to get the
 temporal GIS paper ready before adding to much information ... .

 Soeren

-- 
Ticket URL: <https://trac.osgeo.org/grass/ticket/1562#comment:13>
GRASS GIS <http://grass.osgeo.org>



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