I'm wanting to georeference an old chart in the same manner described in a published article:
"All charts were transformed to the British National Grid. The 1904 chart was georeferenced using nine fixed landmarks such as church spires, of which the National Grid coordinates were known. Errors due to georeferencing were <0.01 cm, corresponding to a maximum positioning error of 7.5 m on 1:75,000 maps. The accuracy of the digitizer itself was claimed to be +/- 0.127 mm."
My own image has a cell size of 22, has a scale of approx. 1:127,000 and was georeferenced onto a map of scale 1:25,000 using 10 evenly-distributed GCPs. My Total RMS Error is 36.
How do I identify the maximum positioning error as described in the article? I.e. can I convert RMS Error into meters?
Interpretation of RMS Error is well described in this thread: Generally accepted root mean square (RMS) error for rectifying topographic maps. However, I'm not sure how the author obtains an "RMS of 5 m". Is the RMS Error expressed in meters, or is there an additional conversion needed?