Geo Ref tool: log message offsets

There have been some reports of erroneous altitudes being output from the Geo Ref tool:
http://diydrones.com/forum/topics/pixhawk-cam-message-offsets
http://diydrones.com/forum/topics/geotagging-pictures-from-nex-5-using-apm-planner-and-pixhawk

It appears that the log message offsets are incorrect, or perhaps different on Pixhawk vs. APM.

The resulting values that supposedly correspond to altitudes are completely different from the expected/true altitudes, so this is unrelated to incorrect specification of seconds offset. This was verified by opening the data flash log in Excel and filtering the CAM field.

Here is an example of erroneous altitudes written to EXIF metadata, read by Agisoft Photoscan. The images selected in blue highlights have sub-meter altitude values.

And here are the CAM messages viewed in Excel. Column G contains the correct altitudes reported by the GPS:

Start in the Geo Ref tool's CAM log parsing, using the linked forum reports and the Excel CAM-field example to compare the altitude value with the GPS-reported altitude. Done means the tool reads the correct altitude from Pixhawk and APM logs and writes accurate EXIF altitude metadata.

Written by the indexing model from the issue text.