BTW, the “curves” I see in the IGES file for the brick are composed of three straight lines. There are no surfaces other than planes with three lines for the boundary. In other words, the edges and faces appear unaltered. The downside, of course is that a nice-looking dome in SketchUp will end up being a bunch of facets (just like the STL file). At least within the FreeCAD software, no attempt is made to generate NURBS or other surface types beyond a flat plane in the IGES format.
There is one other entity, the 402 (Form 1) which says that my brick is made of 12 entities, with pointers to each of the straight-line bounded planes. Dissecting the IGES file related to a 24-segmented dome (created using Follow Me), shows 286 line-bounded planes (most of which have three edges, but some have four).
I’m not sure how one would create and export anything like that from SketchUp in the first place … but I agree with dumping the antiquated IGES format. The info I came up with (above) is based on the proposed 6.0 version, circa 2001. I only looked into the IGES file in detail since I’m already familiar with the format.