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#crs
3 posts tagged crs.
Datum-Free PNEZD: When the Numbers Look Like State Plane But Aren't Declared
A PNEZD CSV lands on your desk. The northings are in the 500,000s. The eastings are in the 1,800,000s. It looks like a clean state-plane file -- except nobody declared which state plane, which datum, or which units. Picking 'looks about right' from a dropdown can put your final coordinates 30 to 100 feet off the truth. Here's how to read the file before you import it, what assumptions you can and can't make from the magnitudes alone, and when to pick up the phone instead of guessing.
Local-Grid Coordinates: When 'Northing 5000, Easting 5000' Means Nothing
Older boundary surveys often use an arbitrary office origin instead of a real coordinate datum. The PNEZD looks fine. The numbers add up. But there's no way to put those points on a map without a ground-truth anchor. Here's how to recognize a local-grid archive, what you can and can't do with it, and how to pull it into a real CRS when you have to.
When 'State Plane' Isn't State Plane: The Custom-Scale-Factor Trap
Some surveying firms apply a custom scale factor or rotation to their state-plane work to align with a local monument. The PNEZD output looks like normal state plane to any downstream tool -- but verification points land 5 to 50 feet off. Here's how to spot it, diagnose it, and fix it.
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