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: