[GRASS5] Temporal data in GRASS?

[Helena]

Markus Neteler wrote:

> Hi Carl,
>
> On Wed, Oct 24, 2001 at 11:44:10AM -0400, Carl Worth wrote:
> > Greetings,
> >
> > I'm interested in working with some GIS data that has a rather dynamic
> > temporal element. For example, I plan to record the location of
> > various moving objects, (via GPS), and later I'd like to replay this
> > data in GRASS.
> >
> > I've considered doing something as simple as storing timestamped data
> > in a database and looping through the query results, displaying
> > successive images. But, I wonder if a more integrated solution might
> > not be more desirable.
> >
> > >From what I've seen so far, I haven't seen anything in GRASS that
> > deals with temporal data. (But I am a total newbie to GIS and GRASS so
> > I may have missed something obvious, just let me know.) I can imagine
> > many applications that have temporal elements, (ie. changes with
> > seasons, or from year to year). How have users of GRASS typically
> > dealt with these kinds of data?

Carl,

I have been working with temporal data in GRASS for many years - mostly in
the area
of spatio-temporal interpolation, simulation of landscape processes and
visualization.
You can see some examples at
http://skagit.meas.ncsu.edu/~helena/gmslab/
e.g. http://skagit.meas.ncsu.edu/~helena/gmslab/viz/erosion.html has
simulation of water
and sediment flow as well as insolation during winter and summer solstice
http://skagit.meas.ncsu.edu/~helena/gmslab/viz/sinter.html has rainfall as
it changes during the year
as well as change in pollutants in groundwater and in Chesapeake bay.
Currently I am looking at a time series of 20 years of bathymetry data and
temporal changes in topography
and water flow pattern due to development.
You can represent time either through a time stamp for raster, vector and
ite data, but if you have a moving
object time can be assigned as a string attribute (I think that we do not
have a specific time attribute) for each
site. There is a need to add the time display capability to other modules
such as d.rast, d.vect, xganim and nviz
as well as create tools for seraching and queriyng the temporal data sets
based on the time stamp
(for example I may want to extract the bathymetry data from my 130 files
time series for the dates
when there were big storms). So it would be wonderful if you could
contribute some capabilities, because the
development of time-related capabilities stopped about 5 years ago and many
people would welcome if
somebdoy could take it over. You can have a quick look at the Date-Time
library html docs at
http://skagit.meas.ncsu.edu/~helena/gmslab/htdoc/
(but then you would have to go to the programers manual as suggested by
Markus, it is in PDF or LATEX)
For the moving objects - especially of you have more of them moving at the
same time you can transform them
to raster (s.to.rast) and then animate them by xganim, however, as I am
writing this I remembered that for
the groudwater pollutants data Bill modified display of sites in SG3d so
that it is drawn as it was measured,
so that you can observe where you have a big time gaps in measurements etc.
But I am not sure where that
piece of code is. It would be nice to add it to nviz. If you have any
questions you can email me.

Helena

>
>
> well, currently only two modules are present
> r.timestamp
> v.timestamp
>
> The sites (point data) format also support timestamps.
>
> Then the "xganim" module allows to play selected raster maps as
> film sequence (note, just fixed in CVS).
>
> > If the current GRASS support isn't sufficient for what I need, then I
> > plan to implement whatever it takes. I'm an experienced C programmer,
> > and there are a couple of projects here at ISI that could benefit
> > from this. I would be interested to hear suggestions from more
> > experienced GRASS developers on what the right approach might be to
> > incorporate this into GRASS.
>
> This sounds very good. We are quite interested to fully support
> timestamps in GRASS. A suggestion could be to extend i.group
> (or develop a new module) to group maps according to timestamps
> for later analysis, display or whatever.
>
> Here at ITC we intend to improve the multitemporal image processing
> features, but a general implementation would be the best. GRASS 5
> provides a DateTime library, most (all?) required functions should
> be available on library level. Now it is time to extend the
> appropriate GRASS modules.
>
> Have a look at the Programmer's Manual to read about the DateTime.
> http://grass.itc.it/grassdevel.html#prog
>
> Please let us know your needs.
>
> I would appreciate a collaboration,
>
> best regards
>
>  Markus Neteler
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