A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2016 Jan 28, 14:35 -0800
+/- 2 pixels is to be expected. This translates to about +/- 1' which isn't much. I just pick the center of the Sun by eye after zooming in x4. Calibration is done from a known GPS position on shore and picking a day with no wind and a sharp horizon. Take images every 4 minutes of time from 35° to 1°. Plot on graph paper the corrections in minutes of arc to get a zero intercept for each image. Make the cheat sheet for every 100 pixels by picking off the completed graph. This will make for easy mental interpolating on follow-up images. A little trial and error may be needed to select the two digit multiplier that results in the smallest correction values. A rough starting multiplier can be had by using the Sun's exact diameter from Calsky and determining minutes of arc per pixel from a centered Sun image with the lens to be calibrated.
From: Bill Lionheart
Date: 2016 Jan 28, 13:42 -0800