Barry
Posts: 4
Joined: 2/20/2009

COGO  Grid Scale Factor 
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I am a GIS Project Specialist at a DOE site in Texas, and am attempting to setup a spreadsheet project to convert ground coordinates to grid coordinates (based on TX State Plane NAD83 Fips 4201 coordinate system). Upon reviewing the NOAA Manual NOS NGS 5, "State Plane Coordinate System of 1983", I am attempting to embed the necessary formulae into a spreadsheet in order to partially automate the conversion process. I am simply stuck with the gridscale factor formula. I am stuck pondering how to find out the "mapping radius at the latitude of the mapped location". This is not a constant. This appears to be the one missing link :)



Friday, February 27, 2009 at 5:37:37 PM 
BlackWatch
Posts: 14
Location: Orlando, FL USA
Joined: 10/17/2008

Re: COGO  Grid Scale Factor 
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Barry, sorry to take so long to get back to you. The answer is that the spreadsheet approach likely can't be made to work, as you may have already discovered. The conversion factor is not a constant. You will need to use projection translation software that can do the job right, and then transfer the results to the spreadsheet. It is possible that you could find the equivalents for a grid of points, and then straightline interpolate between the values in the spreadsheet to save some work.


Barry
Posts: 4
Joined: 2/20/2009

Re: COGO  Grid Scale Factor 
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Right, I figured it is not a constant by reading the NOAA manual, "State Plane Coordinate System of 1983", www.ngs.noaa.gov/PUBS_LIB/ManualNOSNGS5.pdf, Pages 26  28. My plan was to apply the formulas in spreadsheet format to each coordinate. I do not know of a software product that converts groundtogrid coordinates. ArcGIS has the option to enter a conversion angle and distancescale factor, but I imagine the distancescale factor is actually the gridscale factor (which of course varies with each location). So, you can see that this is impossible to work with, especially for large areas, as it would require opening the dialog and changing the distance factor for each survey leg. I know, that the gridscale factor is not enough to worry about, but this thought obviously applies less the larger the surveyed area as well, right?
Do you know of a good software package that easily converts ground coordinates to grid?

