Posted By Luke CO PLS on 2/18/2010 at 8:48 PM
Why do some agencies ask for design base mapping to be done at State Plane? Especially when they are in Denver or some significant elevation? So we surveyors do the control and the photo control at State Plane datum. Then the project is designed at State Plane. Then we are doing construction layout. Fine, we just continue to layout at sea level and put the right elevations on things. Done deal. Turns out the road is only 24 feet longer at elevation than at sea level where it was designed. Is this a problem for anyone? Guess not.
Did the photo control on a project (1977) and provided State Plane after trying to change their minds. Months later I get a visit from a Geotech. He shot in a drill hole from our control and it plotted on the wrong side of the trail. He checked his info and it was in order. His jaw hit the floor when I told him to reduce his measurements to Sea Level and it would work. He did not read or understand the note on our topo giving the Combined Factor to convert to ground. I gave him a copy of our two-page letter explaining what was requested and how we felt that it would cause problems for everyone in the future. I still think it causes problems when it is done today.
Now for the AS-BUILTS..…
Is it finally time to admit that the distances and stationing did not really work out up here on the ground? Maybe I will just make a cartoon drawing of an engineer at elevation 4,000 feet sticking his head in the sand (down to an elevation of zero!). Should we admit now at the end of the project that the road is 24’ longer based on the as-built measurements? I just have a problem with stupid sometimes.
Project Design in State Plane - Elev = 4,000 Ft.
February 19, 2010