Thanks for all the responses. I should have been more complete in my request.
In 1769, The American Philosophical Society sent a team of three men to a small town on Delaware Bay, south of Philadelphia and near where I live, to observe the transit of Venus. They determined the coordinates of their observing site by doing a survey to a point of known latitude some 20 miles south of their site. The raw field data (bearing and distance) were published in 1770, as part of the report on the transit observation. I am attempting to locate the location of their observatory as closely as possible from the survey data.
The subject gets complicated in a number of areas; what values did they use to convert distances to degrees of latitude and longitude, what was the magnetic compass declination used and was it correct, how should the survey route be displayed using modern geoid parameters, what precision can be achieved with an 18th century theodolite with hand divided scales, etc.
I have written programs that generate kml files to draw the route on a Google Earth map and it is clear that they used existing roads wherever possible. It is also clear that some of the 120 data points are wrong, which could be due to typographic errors when the data was published, illegible entries in their journal (it was raining the whole time), inaccuracies in the instrument scales, or many other factors. I am trying to reconstruct the route actually taken using old maps and to do so with minimum change to the original data.
There are 120 points that must be considered and I'm looking for a tool to use with Google Earth to evaluate a change from the route derived from the original data to the actual roads (where possible). Almost all of the roads today were there then, so it is possible to do.
I've learned a lot about how to draw on a Google Earth map with kml, how to draw and label connected line segments and how to evaluate the route using the GPS datum (WGS84). Being as I am, old and fat and lazy and stupid, I am looking for a tool that takes some of the tedium out of constructing the real route one point at a time. A protractor that can be moved around the screen, positioned and rotated would be ideal. I think I have seen such a tool, but can't find it now.
I hope this is relevant to the group.
Best regards,
Jim
James E. Morrison
[email protected]
Astrolabe web site at http://astrolabes.org
Astrolabe web site at http://astrolabes.org
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