#1562: Introduction of spatial and temporal vertical units for raster3d maps and
r3.support
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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
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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
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Ticket URL: <https://trac.osgeo.org/grass/ticket/1562#comment:13>
GRASS GIS <http://grass.osgeo.org>