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Re: [udig-devel] Re: DB2 and Oracle support
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Simon Greener wrote:
Jody,
No arcs ;-) The circular arcs are not part of the "Simple Feature"
OGC standard - so nobody in the open standard/source world was that
interested.
Regardless, I have a customer that uses them a lot because road
onramps/offramps
are defined this way in preference to vertex-to-vertex segments.
Ah reality, the bane of many a standards body.
My library reads the arcs though, and prints out warnings.
As above - we have the information, we would just need a data structure
to hold it.
It should be noted that the Arcs are really old tech and that most
modern systems use nurbs (as the "arc" ends up being inside all the
control points). I am sure that was way more detail then you cared
about.
I have no idea what this means! What is a NURB? What do you mean by
an ARC benig
inside all the control points?
NURBS - let me try it "Nonuniform Rational B-Splines". I think that is
right.
A "problem" with the oracle Arc (and Circle) definition is that the Arc
is defined by a three points. If you made a polygon out of those three
points the arc would be outside them. A NURB is a form of spline that is
also defined by points, called control points. It has the property that
the described arc is always within the control points - this makes
things like spatial index systems happy.
As I said - needless technical detail.
As we look into supporting GML3 (and an associated ISO Geometry
specification) we will have an oppertunity to support arcs.
Does this mean that arcs are in GML3 or some ISO/SQL3 geometry type?
So, is the OGC SFS
the problem more than Oracle Spatial?
Yes Arc (and circle) are in both the ISO spec and GML3. I am not sure
if I would call either SFS or Oracle Spatial at fault, each was making
use of the best technology at the time (and both look a bit dated now).
If you are interested let us know.
I certainly am!
Very brave of you, especially after my technical detail above. Thanks
for not being scared off.
This week we are just trying to get Oracle up and running (you are one
of the first users interested in direct Oracle access).
Sounds like you are just starting up a project and are considering uDig?
If so perhaps you can tell us more (if only to outline the basic
requirements).
Cheers,
Jody
