Melita,
It made my whole day to see your math in the last note! I was able to use it to arrive at my earlier calc, done with diff math, of
9.8m. It re assures, and makes sense, to me to get a realistic result, like 9.8 meters of error, for the tiff I geo referenced, instead of the really small number I misinterpreted. Thanks so much, Melita, from me and the other 3 gis analysts on our team, for helping us understand this process better. We have hundreds of historical tiffs to geo reference in the next year.
For the other folks following this discussion: let me try to sum up the process of interpreting the RMS error reported in the link table, using Melita's math :
determine that the figures under the X & Y map columns are lat and long coords The RMS error is then in decimal degrees.
Our RMS error * 3600 seconds = converts the decimal degrees figure to seconds. The RMS seconds * 30.922 = the error, in meters Of course, this is the error at the equator and should be converted to your lat, if you need the extra accuracy. I'll post a follow up thread, showing my RMS error corrected for my lat, after I figure out how to convert it.
I think the definition of the RMS error: the error between the coords of the link points set on the tiff and the coords of the link points set at the same position on the NAIP imagery. I hope someone will feel free to correct my definition, if I'm in error.
Ken