Why do my arcs get stroked into lines when reprojecting data - is there a way to avoid this

From Fmepedia

Q) Why do my arcs get stroked into lines when reprojecting data? Is there a way to avoid this?

A) Quoting one of our support team, arcs get stroked because such features are not considered geodically correct features as they cannot be readily mathematically georeferenced along their length the way points and lines can be. Many other GIS tools (including Oracle Spatial (http://forums.oracle.com/forums/thread.jspa?forumID=76&messageID=638274&threadID=227343)) do not support reprojection of arcs.

It is possible to avoid this happening. If you leave your output coordinate system to be the default <not set>, you can then use the Reprojector transformer to transform your data between different coordinate systems. Within the Reprojector, you can set 'stroke arcs and ellipses' to 'No'. This will force the reprojection to only translate the endpoints and centerpoints of the arc, and not render the arc itself into a polyline.

If the reprojection does not involve a major transformation, such as in the case of simply a change of units or a datum shift, the arc transformation may work well. However, if there is a significant change in the orientation, such as from from an equal area to a conformal conic or mercator, then the points may shift rotationally enough with respect to each other that the arc geometry gets confused and starts drawing ellipses or circles instead of arcs. This is also more likely to happen if the data covers a large rather than a small area.

In FME 2007 with its Rich Geometry Model FME might have the ability to reproject arcs a bit better. It's certainly likely to handle them better if they are part of a longer chain of features.