Offset and Azimuth to Tangent to Parallel
Back in early March, there was a discussion about the tangent and offset method for marking parallels of latitude in PLSS. There seemed to be no software to do this, only tables from old Handbooks.
The attached text file is a JavaScript application that I wrote just to prove that I could. There’s just enough HTML code to make it open in a browser. The rest is JavaScript.
NOTE: THIS IS IN THE EDUCATION SECTION BECAUSE THIS CODE IS INTENDED ONLY FOR EDUCATIONAL PURPOSES, NOT FOR LAND SURVEYING. ANY USE BEYOND THE INTENDED PURPOSE IS SOLELY AT THE USER’S RISK.
The educational value is in seeing the formulas implemented in JavaScript, verifying output against historical table data, understanding the geometry that determines the formulas, etc. While this application seems to come up rarely in the surveying world, there’s always value in understanding the math.
Save the file as .HTML and open it directly in your browser (works in IE and Chrome; not tested in any others.) Data entry is by pop-up, so you may have to enable for the application. You will be prompted to enter LATITUDE and LENGTH OF TANGENT. Output is OFFSET and AZIMUTH. To do another, refresh. Everything happens locally (client-side processing only). There is no access to a server anywhere.
Feel free to examine the code, either in the browser or by opening the file in a text editor. The Clarke 1866 ellipsoid is hard-coded; if you change that, remember to change its label as well.
If you make any improvements, please help us all learn more by sharing them with the rest of us.
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