[geotk] Circle Polygon

theuns theunsheydenrych at gmail.com
Wed Sep 16 07:02:41 EDT 2009

Me and Johann sorted it out.

The circle i am generating with the JTS geom.buffer is generated with a
CRS(3395) captured point , so the values generated is still in
CRS(3395), and like Adrian pointed out is that JTS does not take in
acount the CRS. So when the circle is displayed it still used the
CRS(3395) for the display of the values , hence the round circle.

The suggestion is now to use the geodedicCalculator to work out the
values for the circle, for a certain CRS, this makes more sense to me,
since the geodedicCalculator will take in account the CRS.

Do you agree?

Thanks for all the help

On Wed, 2009-09-16 at 10:24 +0200, Martin Desruisseaux wrote:
> theuns a écrit :
> > I displayed a world shapefile using the EPSG:3395 projection.
> > and draw 4 circles with radius 50km.
> > 
> > This is the places(more or less) where i draw them , and i measured the
> > diameter across the with and height, of the circle.
> > 
> > 1. Equator , width +-100km , height +- 100km 
> > 2. Cape Town (SA) , width +-82km , height +- 82km
> > 3. Southern Tip of South America , width +-57km , height +- 57km
> > 4. Northern Part Greenland , width +-14km , height +- 14km
> > 
> > So the circle's diameter does take off further away from the equator,
> > and like Adrian said, it should be egg shaped (eclipses), but the circle
> > stay round?	
> This is true that if the Data CRS is Mercator and the renderer Objective CRS is 
> Geographic (or the converse; Geographic Data CRS and projected Objective CRS), I 
> would expect egg shaped ellipses. If both the Data CRS and Objective CRS are the 
> same projection, then the shape would stay as in the data but I would not expect 
> a change of circle size neither...
> In order to figure out what is happening, I would need to know the rendering 
> chain: data CRS, objective CRS and which API is used for rendering the circles...
> 	Martin

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