On Wed, Jan 14, 2009 at 10:36 AM, Martin Spott <martin.sp...@mgras.net>wrote:
> 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_.
I've always lobbied for using the GSHHS shoreline database because I feel
that is the best shoreline database we have available. However, for a
variety of reasons we have ended up using political boundaries of VMAP0
which as you state is less than ideal. (1) VMAP0 has some significant
inaccuracies (2) assuming anything outside of political boundaries is ocean
causes the great lakes in north america to be rendered as ocean at 0 MSL.
I still would like to find a way to move back to the GSHHS data set if we
can figure out a way to resolve problems with combining that data set with
VMAP0 freshwater data (which often conflicts with GSHHS ... things GSHHS
considers freshwater might be considered outside political boundaries in
VMAP0 and visa versa so you can't marry the two data sets cleanly.)
Sorry, didn't mean to press the wrong button here, but just wanted to
provide some realistic feedback. I think the problems will be more
difficult than you imagine, but certainly you are welcome to push forward.
Every scheme has pluses and minuses, so if you can push through the
difficult portions, maybe you will be able to come up with something better
than what is available now.
Regards,
Curt.
--
Curtis Olson: http://baron.flightgear.org/~curt/
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