## Grid and Ground Distances

## Grid and Ground Distances

(OP)

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 accurate do you need your distance?

## RE: Grid and Ground Distances

## RE: Grid and Ground Distances

## RE: Grid and Ground Distances

## RE: Grid and Ground Distances

1 Jan 075-10. 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