Re: Ellipse Data Type? Best practices for elliptical data? [Oracle 9i Spatial]

On Tue, 18 May 2004 17:37:02 GMT, "C Wilks" <cjwilks_at_hotmail.com> wrote:

>> Are you trying to set up a new datum or coordinate system? Oracle does
>
>I will just be using a standard geodetic spatial reference system, probably
>WGS84 from what I can gather so far. I'm just trying to store geodetic
>ellipses, and then compare them with other shapes using the standard spatial
>predicates.
>
>For each ellipse entered, I'll know the center lat/lon, major/minor axes,
>and rotation angle.
>
>In 10g - it appears there is a function SDO_UTIL.ELLIPSE_POLYGON() that lets
>you approximate an ellipse using this information. Does anyone know what
>kind of SDO_GEOMETRY this function generates? (i.e. how does it approximate
>the ellipse?).
>
>In 9i - it looks like you'd have to do the calculations manually to
>determine enough perimeter coordinates to create a polygon out of multiple
>arcs. Does anyone know how to do these calculations? and/or could you point
>me to an article or URL that would shed some light on it?
>

In common with most GIS, I would expect it to do so by generating straight lines approximating the ellipse. Very few GIS (if any) implement any other form of geometry, and it is not required in any of the standard OpenGIS standards, though it is available in GML version 3.0 and the relevant ISO standards.

Paul Received on Tue May 18 2004 - 12:45:52 CDT