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Re: [udig-devel] Local File Format
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On 5-Mar-06, at 5:33 AM, Jody Garnett wrote:
I did try to review the FDO API, as I had heard good things about
it. But at the time it was locked away behind click through
agreements. I trust our new feature model we are rolling out will
be a superset of what they can support. Do we have any contacts in
the FDO community?
Sure, Bob Bray at Autodesk is a friendly soul and can provide
pointers. They may already have some Java wrappers on FDO, for all
we know.
I possible I would prefer to port their C++ code rather then go for
another set of wrappers. HSQL is nice and small but lacks many
normal database features, derby was also floated as an option. Our
firends at OpenJUMP also had a discussion of creating an analog of
the Geodatabase format.
Yeah, exactly, there is a cacophony of talk about other on-disk
formats for our Java GIS community, and it is really dumb! If we
create another format, we create another walled garden for users to
try and break out of. If we start with a format that already has (a)
translator support and (b) application support, we add value to
everybody, rather than just to ourselves. I also respectfully
disagree on porting, since wrapping the FDO API gives us access to
anything that someone happens to add to FDO in the future, while
porting the FDO support for SDF to Java gives us support for just SDF.
If I can phrase this another way I would rather use PostGIS as a
local datastore, as I don't need C++ wrappers to talk to it. Indeed
if we limited the local datastore to being SFSQL happy we would
have a better baseline for some of the join work gabriel is working
on.
PostGIS cannot be a local data-store, since using it involves
installing a whole RDBMS. SDF is on top of SQLLite (which, like BDB,
can run inside the application process), so there is a SQL engine
inside there.
Paul
Jody
One of the things our recent MoF project has highlighted to me is
that as we start adding serious geoprocessing abilities to uDig we
are not going to be able to dodge the need for a local file format
to hold intermediate results. The MoF project was lucky in that
Shape format was not too constraining, and there was really only
no intermediate file anyways.
We have sort of initially drifted towards the idea of using a
beefed up version of the existing hsql datastore, adding some
spatial indexing ability. I want to put another, better (harder!)
option on the table.
How about using Spatial Data Format (SDF)?
What is SDF? It is the "native" format that the new Autodesk
Mapguide Open Source uses.
Why would we want to use it? Let me count the ways:
- There is already support for SDF being added to OGR and FME, so
people who create SDF files in uDig can translate them easily to
other formats using tools other than uDig. This will not be true
if we roll our own on hsql.
- The whole Autodesk product line has support for SDF, so even
AutoCAD will be able to open uDig files.
- The SDF format lives behind an abstraction called FDO (Feature
Data Objects). If we can read/write from SDF via FDO, we can read/
write from all the other FDO formats too. Because OGR is getting
an SDO bridge, this also provides us a route into all the OGR
formats as well. (From an implementation PoV, this also gives us
two routes to choose from: implement an OGR datastore and get to
SDF via OGR's FDO support; implement an FDO datastore and do the
reverse.)
I think the "network effects" argument for doing SDF (and FDO) is
very compelling.
Why not use it? I guess the problem of doing more C++ wrapping is
part of it. And ignoring an hsql datastore that is 80% done hurts
too.
Another option would be to use the new ESRI Geodatabase format,
which does not use Access any more. That format is not fully
baked yet though, and I do not think it is an open one. In
general though, I am becoming enthralled with the idea of using,
not inventing, a local format.
P
_______________________________________________
User-friendly Desktop Internet GIS (uDig)
http://udig.refractions.net
http://lists.refractions.net/mailman/listinfo/udig-devel
_______________________________________________
User-friendly Desktop Internet GIS (uDig)
http://udig.refractions.net
http://lists.refractions.net/mailman/listinfo/udig-devel
