Re: [Geotools-devel] Interface to represent linear geometries?

[Bryce L N. <bno...@fs...>]

geo...@li... wrote on 06/21/2007 06:15:11
PM:

> My stab at an interface representing a LinearGeometry for Linear
> Referencing is attached.
>
> Note that I used only primitive data types and arrays of primitive
> data types to maintain interoperability. In my final implementation I
> would provide a wrapper to this that allowed the use of JTS geometries
> and an Angle object as parameters.

Looks like GM_GenericCurve will get you 90% of the way to where you want to
go.  This is implemented by GM_Curve and by all GM_CurveSegments.  It's not
quite clear from your interface what exactly happens between the two
endpoints of your LinearGeometry.  If I may assume that you linearly
interpolate, then you're talking about a GM_LineSegment.  19107 provides a
library of pretty well constrained paths (GM_Arc, GM_ArcString,
GM_LineString, GM_Conic, etc.) to join the two ends.  Plus, it'll let you
join any combination of curve segments ("paths") end-to-end to form a
single curve.

Look at GM_GenericCurve & subinterfaces:
http://geoapi.sourceforge.net/2.0/javadoc/org/opengis/spatialschema/geometry/geometry/GenericCurve.html

"getPerpendicularDirectionToPoitnOnLine()" needs some conceptual work. In
2D, there's really 2 perpendicular directions.  In 3D, there's a
perpendicular "disc".  However, in 2D, you should be able to use
"tangent()" to get a vector, calculate the azimuth angle, then add or
subtract 90 degrees.  I would write an adapter class to operate on any
curve, and I'd rename the function to "normal()". :)  But that's just me.

"isPointOnLine()" is really "TransfiniteSet.contains(DirectPosition)"
http://geoapi.sourceforge.net/2.0/javadoc/org/opengis/spatialschema/geometry/TransfiniteSet.html

This means that to get "isPointOnLine()", you're dealing with Curves and
not CurveSegments, as Curve inherits from TransfiniteSet.

In short, code against GeoAPI 19107 interfaces and use whatever
implementation suits you. :)

Bryce