Best-Fit Surafce?

I have a existing surface (a surveyed road), which I need to raise 70mm and create a new best-fit surface from it. The new best fit surface can only be a maximum of 15mm plus or minus from deflection points in the exiting profile of the raised surface. Is there a best fit method to do so? Please feel free to ask me more question if need be, thank you.

We do add to existing all the time tolerance then is 0.0, 15mm +- you will be pushing it, how long have you been designing roads. Why the tolerance if an Asphalt overlay sometimes have to go more than 15mm. Only time I worked to +- 3mm was for a high speed car test track at 100mph a bump will send the car in wrong direction when driving hands free track had a collapse in one section the driver was visibly shaken when he got back to the office, bit of a wild ride.

This whole process to me is silly, but its what the contractor wants. Basically the client is testing the road for the magnitude of bumps using the IRI system. So he wants me to smooth out the existing surface, so as of now I'm off-setting the existing profile 70 mm (actually 700mm because of 10 to 1 exaggeration, anyways,) then drawing lines as long as possible, but also trying to follow the existing profile as best as possible to stay within the tolerance of +/- 15mm of the existing profile (150mm due to 10 to 1 exaggeration). Also the client much rather the "new best fit be above (+) instead of below (-). What a headache this is. Maybe Bentley softeare can do this? I don't know, someone please help though..

I'm not familiar with the IRI system although I presume it is a system where a car drives on the road (with multiple cameras & sensors) to measure the ride quality etc? Quite a few Councils use this every few years to assess their road networks.

I can't think of an easy way to do it in Civil 3D. Even if the road centreline was surveyed every 10m or 20m then will it really take that long to do manually? How long is the lengths of road(s)?

I haven't tried it although have you tried CadTools which has a "Best fit, 3D-polyline regression" tool.

How was the existing road surveyed. If by GPS (or even worse LiDAR or similar) then there will be likely be 30mm + of error in the survey already.

Only time I worked to +- 3mm was for a high speed car test track at 100mph a bump will send the car in wrong direction when driving hands free track had a collapse in one section the driver was visibly shaken when he got back to the office, bit of a wild ride.

I've seen +/- 2mm for a competition athletics track. I've also seen mining company's requiring +/- 2mm tolerance in their tender documents for mining haul roads...

We use a 3rd part add on ARD it has the ability to show on the screen multiple constraint lines this could be property lines or often a graded line from a control line, in you case we woud just use the existing levels and add 85 & 55 in two colours these appear on our vertical design screen so we can see straight away also even simpler we have the difference turned on so can see if more than 85. Civ3d should be able to do this display diff others will help.

Like Organic our surveyors will only guarantee around 20mm. Lidar all over the place +ve 1 spot, -ve then next, the next 2mm diff. GPs can be really good and suddenly not so good.