Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Grid and Ground Distances

Grid and Ground Distances

Grid and Ground Distances

Hi, what is the difference between grid and ground distances? If I have coordinates between two points (measured by a GPS) and measured the lenght between these points, is that considered ground distance?

RE: Grid and Ground Distances

How far apart are the two distances?

How accurate do you need your distance?

RE: Grid and Ground Distances

Around 60 meters, but this distance was measured with a total station. The GPS coordinates were affected with a correction factor, so I am assuming that these distances are ground distances. Is this correct ?

RE: Grid and Ground Distances

No elevation change?

RE: Grid and Ground Distances

Elevations changed a bit, since GPS Elevations were also affected by the correction factor.

RE: Grid and Ground Distances

See EM 1110-1-1005
1 Jan 07
5-10. Grid Elevations, Scale Factors, and Convergence
In all planer grid systems, the grid projection only approximates the ellipsoid (or roughly the ground), and “ground-grid” corrections must be made for measured distances or angles (directions). Measured ground distances must be corrected for (1) elevation (sea level factor), and (2) ground to grid plane (scale factor).
Figure 5-9 below illustrates a reduction of a measured distance (D) down to the ellipsoid distance (S). Not shown is the subsequent reduction from the ellipsoid length to a grid system length. Observed directions (or angles) must also be corrected for grid convergence. Also shown on the figure is the relationship between ellipsoid heights (h), geoid heights (N), and orthometric heights (H).

If there is no change in elevation, over 60 meters, just how much change are you expecting based on the earth's nominal radius of 7000 odd kilometers?

RE: Grid and Ground Distances

racookpe1978, thanks for taking the time on this. Our coordinates and elevations for benchmarks determined by GPS were corrected using correction factors to account for the sea level and scale factors. After corrected, we set up other benchmarks using a total station. I think that since we have corrected our original BMs (determined by GPS) and then established new BMs using a total station, our distances are ground distances. Thanks again for your replies.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close