"Curtis Olson" wrote:
> On Wed, Jan 14, 2009 at 9:35 AM, Martin Spott wrote:
> > Secondly, <PROPER DESIGN> using bathymetry 'elevation' data we'd
> > certainly be able to create seabed 'Terrain' for "Ocean" and probably
> > also for "Lake" areas </PROPER DESIGN> - probably not as detailed as
> > the regular surface but sufficiently accurate to model the seabed for
> > example within the twelve mile limit (just to put a figure). This would
> > allow for simulation of tides and the resulting effects at a later
> > development step.
> My sense is that there are many areas in the world where the slope of the
> shore line is very shallow. Also don't forget that our SRTM data has a
> resolution / random noise element of about +/- 5 to 10 meters. I think that
> these things combined together could lead to some extremely inaccurate
> shorelines and odd contour artifacts if we try to physically model the water
> level and the terrain elevation to create a shoreline.
>
> It's a neat idea and certainly could be worthwhile territory to explore, but
> I'm pretty sure it will yield highly inaccurate shorelines with ugly
> artifacts in many areas of the world. And there are many hidden dangers I
> would think. If we get the ocean level off by a meter or two and the land
> off by a meter or two, we could have unintended side effects such as putting
> all of KSFO under water at high tide.
Well, currently we're 'adjusting' the Terrain to a hypothetical
shoreline in a very simple way: Everything that lies within the VMap0
definition of political boundaries (our current coastline) is defined
as ground and any SRTM point that lies outside this area is getting
ignored - even if it lies remarkably above MSL, no matter if the SRTM
elevation and/or our coastline are valid or not. I don't see any reason
not to apply the reverse schema to bathymetry data.
The real cause of trouble is not our elevation data, it's the coastline
- due to the corresponding landuse data we're currently using.
As a side note: Before disesteeming my approach as being just "a neat
idea", your "sense" should get an update about the accuracy of
SRTM-derived shorelines (SWBD et al.). I know, they _do_ have huge
inaccuracies, notably at mudflats, but in the overall picture they're
not much worse than our current approach of telling between ground and
sea.
And your sense should also get an update about all the small airfelds
and large airports which are sitting out in the sea _now_.
Think about it,
Martin.
--
Unix _IS_ user friendly - it's just selective about who its friends are !
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