[GRASS-user] Re: [GRASS-dev] vertical units New module for lake filling - r.lake

[Markus Neteler]

On Fri, Jul 07, 2006 at 04:16:49PM -0700, Dylan Beaudette wrote:
> On Wednesday 28 June 2006 17:24, Helena Mitasova wrote:
> > On Jun 17, 2006, at 5:26 AM, M??ris Narti??s wrote:
> > > Re-posting, as previous mail was larger than lists accept.
> > >
> > > Hello all GRASSers.
> > >
> > > GRASS CVS contains new module r.lake. This module can be used to
> > > create lake
> > > maps if only place and lake level is known. To use this module You
> > > need
> > > terrain raster map (DEM), water level for lake in same units as DEM
> > > values
> > > and coordinates for any point in lake.
> > >
> > > Module uses 3x3 sliding window to fill whole area connected to seed
> > > point (can
> > > be coordinate pair or already existing raster map) and having
> > > height values
> > > below water level. Output map will have lake depth in DEM units. More
> > > information about module is in help page.
> > >
> > > I use this module for palaeolake reconstructions based on single
> > > shore line
> > > measurement. It also can be usefull for reservoir planing, creating
> > > maps with
> > > scenarios for lake level changes etc. Unfortunately mailing lists
> > > does not
> > > accept attachments larger than 100kb - no sample images with r.lake in
> > > action.
> > >
> > > Currently this module has some limitations and I ask for help to
> > > other GRASS
> > > developers to help me to fix them.
> > > Most important - module is NOT large file safe.
> > > Lake volume calculations work only if DEM is in meters.
> > > G_area_of_cell_at_row() always returns cell area in square meters,
> > > but I
> > > could not figure out how to get information about DEM units. Thus
> > > if both are
> > > in meters, volume is correct, else not ...
> >
> > we have already discussed this in relation to r.slope.aspect which
> > has the same problem,
> > currently it gives warning when x,y in feet is converted to meters so
> > that user
> > can check and make sure that the elevation is in meters too.
> > There is no place currently in GRASS to store DEM z-units (and
> > vertical datum) so it is left to
> > the user to make sure that the units are handled correctly (big pain
> > here in US where
> > feet and meters are about equally common and mixed in various ways).
> >
> > I believe that for GRASS7 we should include the vertical datum and
> > units information for each location even if we
> > do not provide the transformation tools - this should help users
> > better manage
> > their elevation and volume data and they can use external tools to
> > convert the vertical datum
> > for the data that they want to import to the datum used in the GRASS
> > location.
> > For example there is an official open source code for US coastal
> > vertical datums conversion
> > available here (it is written in Java2 though)
> >
> > http://chartmaker.ncd.noaa.gov/csdl/vdatum.htm
> >
> > This would not prevent the users to mix misc. vert. and horiz. datums
> > and units in their database
> > (at their own peril as I have learned the hard way), but it will
> > encourage the management
> > of data in a well defined coordinate system and units in all 3
> > dimensions.
> >
> > Helena
> >
> > P.S. I would like to add this suggestion to the wiki development page
> > - apparently it should go
> > under Plans but it does not fit into Overview, should I add it to
> > sand box?
> > Or should we start a GRASS7 proposals/suggestions/todo section?

I have started such a page:
 http://grass.gdf-hannover.de/wiki/GRASS_7_ideas_collection

Please extend.


> >
> 
> Helena,
> 
> Thanks for the overview things:
> 
>  I would be very interested in the inclusion of vertical units and datum 
> parameters. Does GDAL have any notion of such concepts, and if so can we 
> learn from it?

AFAIK it is not really there:
 http://lists.maptools.org/pipermail/gdal-dev/2005-October/006857.html

(use
 http://64.233.183.104/search?q=cache:-4Cfx1cdvooJ:lists.maptools.org/pipermail/gdal-dev/2005-October/006857.html+gdal+vertical+datum&hl=en&ct=clnk&cd=3
 unless the maptools.org/gdal.org DNS problems are solved)

Markus