Hi,
Dene, I'm very sorry that we won't be able to integrate your current
work directly. The main problem here is that the database stores
primitives in order to allow easier modifications of larger scale. It
might be technically possible to extract polygon primitives from the
.btg.gz files (see at the end of this mail), but for line data we're
practically lost (as practice shows, point data is actually of no use,
except perhaps for placing predefined objects - wells, transformer
stations, etc. - automatically, which is a totally different issue).
Furthermore, we want the database to provide a logical view on the data.
This means that the object attributes in the database should actually
tell us more about a primitive than its material or - in case of lines
and points - its width/size. This way we can change the material
assignments based on logical information (instead of presentation
information) in case we're making progress in terms of the standard
material database.
Maybe one day we'll have a terrain engine in FlightGear which can grok
the primitives directly (maybe including dynamic level-of-detail and
thereby allowing more accurate base data). In that case, the
modifications in the database will still be of use, while the direct
tile modifications will be lost.
And, as Martin already said, we're not getting in trouble if, e.g., new
elevation data can be used for the scenery, or similar.
So, we have - as we think ;-) - good reasons for our decision and we
regret that this means that many current modifications cannot be
integrated. However, we hope to eventually get all of you into the boat
with appropriate tools, etc.
And yes, I'm still working on the tutorial and the tools ;-)
Martin Spott schrieb:
Frederic usually
makes sure that FGSD runs on Windows, there is QGIS on Windows which
makes a nice viewer, there is uDIG which runs on Windows as well (as
it's written with Java/Eclipse), GRASS is available on Windows (although
this might be a tricky part ....).
Well, GRASS on Windows is entirely possible, although with some
usability problems and it needs some tricks for compilation. However, I
think that most of the usability problems can be circumvented by using a
combination of QGIS/GRASS, which seems to be a good idea anyway,
regardless of operating system. In that case, QGIS is more than a nice
viewer ;-) and provides nice replacements for the problematic GRASS
modules. Haven't yet tried it on Windows, though.
Regarding the extraction of polygon data from .btg.gz: The main effort
in creating custom scenery in any form is digitising the shapes, so
something like that might actually be useful.
The data in the current scenery is nothing more than a non-minimal
planar partitioning of the original data. Let a boundary be a polyline
connected to a node on each side. In the beginning each vertex is a node
and each edge is a two-point boundary. A boundary can be removed if both
faces it participates in have the same material. If a node is connected
to exactly two boundaries, it can be removed, joining the two boundaries
to one.
The result would actually be an appropriate input for GRASS, as GRASS
uses planar partitions for topology. One would only have to relabel the
data in GRASS by the logical data and possibly introduce additional
boundaries where the distinction by material does not match the logical
distinction. A bit of manual cleanup might be required as well
(non-matching vertices on tile borders).
Regarding line data I currently have no idea how to solve that.
This way we could at least save some part of the work done directly on
the tiles. Maybe someone wants to give it a try.
Best regards,
Ralf
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