Magnetic to True to State Plane Grid Bearing Conversion

murphy · 2026-05-14T19:04:13Z

Occasionally, I have a need to convert an old magnetic bearing to a NC State Plane Coordinate System NAD83-2011/2010.00 (NC-Grid) bearing. I struggle to understand magnetic to true north conversions when there's an overlap between the declination and the bearing. In my scenario today, I needed to recreate a boundary line in an extremely poor area where next to no actual surveys exist. There was no evidence of possession. Parol evidence suggest the small one-acre parcel was never occupied. I have no better evidence than a 1947 magnetic bearing of N 2deg 30' E to establish the eastern boundary (historic aerials were reviewed). I'm going to hold that bearing and fix it to an old gum tree that I'm hard pressed to prove isn't the tree called out in the creation deed. Now I need to convert the 1947 magnetic bearing to a NC-Grid bearing so it can be set to a relative precision of 0.12' (Class B NC) with base/rover RTK. I'm not confident I did it correctly but I'd like to fill this gap in my knowledge. I put the attached notes together in an effort to save myself some time the next time this problem presents itself. If anyone is willing, I'd appreciate a check on my calculations and would love a more concise explanation or graphic to use for future calcs. Thank you, Murphy

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Strictly Surveying

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holy-cow

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I had to memorize a couple hundred magic formulae to survive my engineering studies. The big trick is to remember the units of each item in the formula.

Posted : May 18, 2026 9:16 pm

mathteacher

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Well put; we're all different. The formulas stem from the concepts, so there's no reason to not know both, but what to apply is an individual decision.

Posted : May 19, 2026 4:48 am

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Magnetic to True to State Plane Grid Bearing Conversion

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