AutoCAD Civil 3D

[#1]

Why would you ever think that you need to design at State Plane Grid? All Surveying will be done on the ground and the difference in length is approximatly a tenth of a foot for every thousand feet in elevation.

[#2]

There are good reasons for designing on State Plane, and it fixes many problems, at the cost of potentially creating the grid-to-ground problem.

But again, I would ask that we not start discussing this topic in this thread, as it is irrelevant to the OP's question, and it is impolite to co-opt a thread.

-- Sinc
http://www.ejsurveying.com
http://www.quuxsoft.com

[#3]

GeoTechnical,

Good Name by the way. I would love to here all about both sides, but I do agree with Sinc. It would help the flow of the Forum (searching ex.) if we started a new Post. Please do. I would but have little knowledge of both topics, hence my original question. I do think Autodesk Forum is a good place for this discussion too. I will subscribe to your Post!

Thanks
Joe

[#4]

Discuss this with the surveyor. He likely set his primary control using GPS. Most of the time (but not always) GPS units will report grid coordinates. If you scale the coordinates up to surface, you are best to use a point that is fixed on the ground (ie. primary survey control point) and close to the center of the project, so the grid and surface coordinates are the same for that point. With a small site, the surveyor can stakeout the project using either grid or ground coordinates and be OK, assuming it is typical development stuff, ie roads, sewers, drainage, etc. If you scale based on 0,0, you will shift the entire site a significant amount...usually 2 or 3 feet. This can cause havoc when re-establishing survey control and staking out the project.

[#5]

According to my calculations of the OP's scale factor and project size there
would be approximately 1.5 feet of difference when comparing grid to ground
distances. I would hardly classify that as close enough for typical
development staking.

Personally I would never supply our design staff with grid coordinates to
design from. Typically we supply ground distances with a CSF. All work is
designed and completed at ground yet the have the CSF if they need to import
georefenced files of any sort like images or GIS data.



wrote in message news:6391804@discussion.autodesk.com...
Discuss this with the surveyor. He likely set his primary control using
GPS. Most of the time (but not always) GPS units will report grid
coordinates. If you scale the coordinates up to surface, you are best to
use a point that is fixed on the ground (ie. primary survey control point)
and close to the center of the project, so the grid and surface coordinates
are the same for that point. With a small site, the surveyor can stakeout
the project using either grid or ground coordinates and be OK, assuming it
is typical development stuff, ie roads, sewers, drainage, etc. If you scale
based on 0,0, you will shift the entire site a significant amount...usually
2 or 3 feet. This can cause havoc when re-establishing survey control and
staking out the project.

[#6]

Mike, you are right. That is significant even on typical development staking. I work in an area at much lower elevations so we dont see nearly that much difference between grid and surface and its not really a big deal unless you have a 10 mile road job. Sorry for my closed-mindedness. I dont know that I can suggest anything except get with the surveyor and figure out how to satisfy the plan reviewer cause it is a big deal.

[#7]

MJP42,
Where are you located that your coordinates only move a few feet when applying a ground scale factor? In my part of Texas, a shift of 1200-1500 feet is the norm if applied at 0,0.



For the original post, be aware that if you scale objects using autocad, the z value is affected also.

[#8]

Transforming Grid to local system does only involve one Convergence and Scale Factors values. In fact, there are practically infinite number of convergence and scale factor values involved. One must have working knowledge in geodesy.

Construction people can not just impose their coordinate system. They must undergo training on how coordinate systems relate.

Arnel M. Domag
nth geographics and geometrics