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Setting the Shape Accuracy Options

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Most of the output options do not have native support for rectangles and ellipses. For these options (KML, SVG, HTML), MPExporter converts these shapes into closed freeform shapes. The accuracy of this conversion is controlled by using the the Shape Accuracy Options dialog box. This is displayed by pressing the Set Shape Accuracy button on the main MPExporter dialog box, and looks like this:




The setting for the Rectangles determines the number of points (vertices) to be used on each side of the rectangle. It can range from 2 to 30. A higher number will be more accurate but it will tend to result in slower processing and a larger export file.


The setting for Circles and Ellipses works in terms of percentage error. This ranges from 0.001% to 5% of the radius. For example, 1% error on a 2km radius circle will result in a maximum error of 20m (0.02km). A smaller error will be more accurate but it will also tend to result in slower processing.





The appearance of rectangles, circles, and ellipses in MapPoint will depend on MapPoint's current view. MapPoint aligns shapes relative to the screen coordinates, and not map coordinates. I.e. a shape will appear to move slightly as the view moves. The best MPExporter can do, is to align the shape relative to map coordinates.


Rectangles and ellipses are flat Euclidean shapes. These are being projected onto a near-spherical globe. This is impossible without some distortion, although this is usually only visible on larger shapes. MapPoint ignores this distortion.


For the SVG option, the circles, ellipses, and rectangles are all converted to map coordinates before the projection to the final map coordinates. The projection may result in some apparent distortion of the shapes, but it does mean they will cover the same areas of the map as they do on MapPoint.


Maptitude has native support for rectangles and ellipses that is used by MPExporter. This native support allows for maximum fidelity with minimum memory usage.