Hi Martin,
We appreciate your efforts. I'm sure most engineers understand that often
we put in a ton of work under the hood for few outwardly visible results ---
and can work in that mode for quite some time, but at some point the pieces
do start coming together and the results begin to quickly emerge. But then
whatever the result, that quickly becomes the normal baseline of
expectation, and we will just want more. :-)
Curt.
On Tue, Dec 21, 2010 at 7:45 AM, Martin Spott wrote:
> Hi folks,
>
> traditionally I'm rather silent (at least to my own understanding)
> about what I'm trying to achieve within the FlightGear project. On one
> hand I'm proud to be, most prominently, known either as the person
> who's rejecting submisions to the Scenemodels repository for unfounded
> reasons or the one who still didn't manage to get a new World Scenery
> release out for two years :-)
>
> On the other hand these are just side-effects of what I'm trying to
> achieve. Instead, the underlying goal is to compile a _seamless_ (to me
> this is important in almost every respect !!) set of raw data for
> building Scenery - 3D models as Scenery-'decoration' as well as
> Terrain. As a side note, I personally consider our collection of 3D
> models (in AC3D format) as being just another flavour of "raw data" in
> this context, suitable - similarly to the Terrain - for getting
> compiled into whichever current or future custom format, if required.
>
> I'm not posting this article for the purpose of fishing for
> compliments. Instead I'm trying to give a rough idea of what I've
> actually been doing in my spare time over the past years - and, last
> but not least, to outline that there are _huge_ differences between
> various efforts which are abiding by the term "Scenery development".
>
> You'll find one isolated example of the stuff I've been dealing with
> exposed in this little mailing list thread:
>
>
> http://postgis.refractions.net/pipermail/postgis-users/2010-December/028415.html
>
> A few words about the background to this case:
> Some people have been contributing custom land cover data. Now, in
> order to create a 'seamless' landuse coverage, we're cutting a precise
> hole into the stock VMap0 coverage, well-suited for seamlessly (!)
> inserting custom data. To make it evident, please have a look at a
> sample of John Holden's recent work:
>
>
> http://mapserver.flightgear.org/map/?lon=-72.05396&lat=44.16884&zoom=12&layers=B000000TFFFFFFFFTFFFF
>
> On the right you'll see VMap0 polygon data, on the left there's John's
> customized land cover. The PostGIS extension to the PostgreSQL database
> is not only capable of storing all this polygon data but also provides
> the required functionality to do the mentioned hole-cutting directly in
> the database, without copying not even a single polygon in or out. You
> just have to call a set of properly selected SQL commands in the
> correct order.
> I've written a proof-of-concept shell script which does this almost
> automagically, but I'm finally running into trouble - see the above
> mailing list posting - which is holding me back from proceeding with
> the integration of more land cover data.
>
> Another item regarding 'seamless' land cover is the inclusion of CORINE
> land cover data into our coverage. Just recently - compared to how long
> CORINE data had already been available - the EEA changed the license,
> thus allowing to make use of it for FlightGear Scenery under well-
> established/-proven conditions.
> After close inspection of a couple of unexpected crashes it turned out
> that CLC is strikingly inaccurate with respect to its topology. There's
> a pile of adjacent polygons whose borders don't align properly, leading
> to holes or overlapping areas. This doesn't hurt much if you're
> building a reasonably small and/or isolated piece of Terrain from CLC,
> but ends up in huge trouble when attempting to integrate this with our
> 'general' coverage, or even when building Terrain at some particular
> areas.
>
> Casting all this CORINE data into clean topology takes several weeks of
> processing time, when performed properly. Even doing tests on small but
> still representative areas is a rather time-consuming and ressource-
> intensive adventure - some early tests on the Europe-wide dataset ran
> out of memory on a 32-GByte-machine - and occasionally surfaces
> software- or documentation-flaws.
>
>
> In fact, dealing with this flavour of issues, reading, inspecting,
> debugging 3rd-party-software or -documentation is what consumed most of
> my FlightGear-related spare time budget over the past years. This sort
> of "Scenery development" is substantially different from craving for
> aaah's and oooh's on The Forum after you successfully managed to follow
> an elaborate and nicely illustrated recipe on how to build FlightGear
> Terrain. Essentially, if I were depending on public praise as
> motivation, I would probably have shelved my effort years ago ....
>
> I hope that, by putting this article together, I managed a) to provide
> some understanding about why some long-awaited World Scenery features
> are still not ready for production and b) maybe attract some general
> interest into the related topics.
>
> Have fun,
> Martin.
> --
> Unix _IS_ user friendly - it's just selective about who its friends are !
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--
Curtis Olson:
http://www.atiak.com - http://aem.umn.edu/~uav/
http://www.flightgear.org -
http://www.flightgear.org/blogs/category/curt/<http://www.flightgear.org/blogs/category/personal/curt/>
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