James Turner wrote:

> I think part of the problem is that you (Martin) have looked at this  
> too much, and the rest of us (except Curt) not so much. Can you  
> explain for people like me the pipeline you propose to assemble the  
> data (i.e what pieces of the final result come from what source, and  
> how), and how that would fit together at runtime?

To the current state we have a coastline around each 'isolated'
continent or island which is either made from a single closed polygon
(which could be GSHHS) or from the outline around a couple of adjacent
polygons (VMap0 political boundaries). To get an overview, please check
here:

  http://wiki.osgeo.org/wiki/Geodata_Repository#PostGIS_serving_vector_data

This coastline is the basic factor for a simple principle: Everything
inside this coastline is counted as ground, the entire area outside the
coastline is "Ocean". The same principle applies to lakes - just in the
reverse order: Everything inside the lake shoreline is water.

So, even if our STRM elevation grid would indicate some sort of
elevated ground outside our coastline, it's going to get clipped out
due to the given principle. In contrast, if there's no elevation data
for an area inside the coastline, then the ground is still going to get
extended in accordance with the coastline ....  but at sea level.
There's a nice example for these corner cases if you approach RWY 24 at
TNCE in the 1.0.1 Scenery.

I'm proposing a similar but somehow opposing schema (talking is cheap  ;-)
Let us have the seabed modelled using bathymetry data, clipped against
the same coastline which we're using to clip the ground elevation,
limit the maximum 'elevation' of the seabed to the elevation of the
respective coastline, which is presumably at MSL for all ocean
shorelines - or the individual elevation of the respective lake.
Probably limit the seabed elevation to a few centimetres below to allow
for some nice waves ....
I don't see any reason why and how this approach would set KSFO under
water.

> Also, is global (even crude) coastal bathymetry data available?

Yes, I even had a copy of global bathymetry data on my local disk few
years ago, but lost it due to sort of a crash (well, the data is still
sitting there, but I have to re-assemble the partitions before I'm able
to read it).

Cheers,
        Martin.
-- 
 Unix _IS_ user friendly - it's just selective about who its friends are !
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