// This code returns incorrect value after ellipse insertion.
segkey.ShowBounding(out HPS.BoundingKit bk);
// To get correct value, it is nessessary to calculate using ellipse’s attributes.
ellipseKey.ShowCenter(out points[0]);
ellipseKey.ShowMajor(out points[1]);
ellipseKey.ShowMinor(out points[2]);
Is this standard usage?
Best regards
Hey @takase! First off welcome to our forum. 
For most usage, such as a quick frustum culling check, a crude (and probably oversized) bounds is sufficient (for elliptical objects I’m pretty sure it just wraps a sphere around the center larger enough to cover the farthest axis points), and that is what showing the bounds will probably give back. 3DF has Compute and (added later for more options) Filter CircumCuboid/Sphere functions to generate better bounds, which will tessellate curves for real points; HPS should have something similar.
Hope this helps!