I have seen several discussions regarding the merits of creating alignments by picking the polyline vs. by layout. I know Dana is already starting a reply by this point, but this is not what my question is about - yet and there are a couple more things coming up that should get an equal reaction from her. What is really bothering me is the fact that VERY rarely will the bearing reported for any given line on the layout I work with EXACTLY that bearing. They almost certainly an offset of some existing land line, boundary or right of way as determined by our surveyor. He shoots the points, draws a line between, lists it and we have our bearing established - until we max out the angle units precision factor that is. When he does the same thing for the line +/- 90 degrees from the first and we commence offsetting in earnest, we have the starting point for all sorts of lines that don't touch or overlap - and there goes Dana's keyboard again but I am still taking the scenic route home. At some point in all of this, the roads start to curve and tangent off into their own non-parallel way to the rest of the world. These curves and their resulting tangents are drawn to the exact central angle or bearing - more bad mojo the next time we run into one of the offsets. I am starting to smell bad topology and in my right of way at that! The first clue I get when this is ignored are when offsets from my centerline either cross or do not intersect. I get around this by constructing my curves by fillet, putting any rounding in the tangent lengths, turn everything into a happy polyline and select my alignment by object.
And finally, my questions:
What happens to all of these lines when Civil 3D creates the alignment by layout? I have heard that to create these parcels, the segments are created not by the actual geometry with its rounded bearings that represent exactly what is on the ground, but by whatever geometric license necessary for every bearing and distance to be exactly what the label says with respect to the drawings precision values. In essence the actual courses seem to be fudged to match the label. If so, this troubles me greatly, especially when the course is on a curve. Are the offset curves true offsets that share the exact same center after the parcels are created? If there are a number of lots along a curve in the right of way, are those true segments of that curve with the exact same center? Is this a seed for more bad topology? Is The Dinosaur full of coprolite?
