Category Archives: X-PAD

Lambert Conformal Conic projections at ground

In keeping with the recent arcane subject series of this blog, I just finished figuring out the details of converting a SPC grid projection (like Utah South NAD83) into a ground system.

This method has the advantage of working in all software packages with a minimum number of system coefficients:

                Origin Lat, Origin Lon, False Northing, False Easting and a single Scale factor

With this method you can exactly duplicate the results you would get from traditional Modified State Plane Projection schemes that involve adding a Combined Scale Factor to a grid system with a single calibration point. While there is nothing wrong with the traditional way, the steps to implement it are different in every field software tool.

With the method that I describe, you just enter a new projection with the five coefficients and you are done.

The short explanation is:

  • Convert the 2-parallel LCC to a single parallel LCC by calculating an equivalent center latitude and the correct scale factor K0
  • Apply the correct ellipsoidial reduction factor with the correct point scale factor for the new projection base point.
  • Compute the correct false northing and easting

While some of the required coefficients are are in the NOS NGS5 SPC manual, I wanted to better understand how they are computed, so I did all the math.

I was surprised by how little information on this subject that I could find on the web, so I wrote a pretty detailed description with a worked example with all of the code that I used. Plus I used the X-PAD field software to validate the results.

If you are interested in this, continue reading this 10-page PDF:

Leave a comment

Filed under Carlson, COORDINATE STUFF, X-PAD