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Good evening all.  I have a land plat for a piece of property that was surveyed and subdivided in 1978.  It is in Carroll County, MD.  The coordinates given are in the 4000 to 6000 range for all points in the subdivision.

I can plot all of the points along with property lines (using azimuths) in Autocad Civil 3d and it appears correct.  However, my Trimble GPS system uses modern Northings and Eastings (NAD 83).

I am not a professional surveyor, so I am stuck as to how to convert the old coordinates into NAD83 in order to stake out these property lines.  I believe there is a simple solution, but, not being a pro, I don't know it!

Any help appreciated.  Thanks

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Hello there.  there are quite  a   few tools out there for conversion of NAD83  however relying on those conversions for what you do next is another story.  Unless you are doing this for fun or as a hobby, i think you'll want to consult with a professional land surveyor locally... good luck and hope this helps..

btw..that is 3 links above..

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Thank you.  It is sort of "fun"...having solar installed on ground mount system and contractor has staked the location, which I believe to be over our line.  

I checked out those sites; similar to ones I have visited in the past.  Perhaps my plat is not in NAD 27 but rather a local coordinate system??  The North and East coordinates are in the 4200.000 to 6500.00 range respectively.  The plat does not mention what coordinate system is used.  May be time for a pro...

Hi Anthony,
These coordinates are to small to be (SPCS) of any Grid. They are more than likely Rectangular Plane Survey done with horizontal distances. Did the plat not say the source of the Bearings or Azimuth as what they are Base on. Or How they were obtained. Your area is within 2300.00 Ft range. My question is how would you go about doing this ,if the plat had no coordinates just calls around the property. How would you obtain your own coordinates. The 1978 Data maybe as correct as it gets, and may still close within reason but you do not know how the distances or the angles were obtained.I would refresh this survey with up to date information. There were and are a lot Land surveys still done in Rectangular Plane Systems this is a flat surface for Horiz. Dist.,most of the coordinates start out assume then they are transformed and rolled to their North then adjusted for closure , the problem is how to make a Flat World Round for GPS. and a round world flat for your plat done in 1978 and now. I suggest you consult a PLS in your area for this knowledge. Since you have no knowledge of this. Conversions from local assume coordinates to SPCS or GPS needs to be a controlled fit,for the circumference of the area of where you are working and for your liability, get help. But as the world turns we as surveyor attempt or bend the rules and take a flat world and make it round and vice-versa because the world must go on and we force a solution. as it is, it is the best we got. But take a look with some people with your same question and see how they solve this problem or did they.

Key words: Datum conversion, Procrustes algorithm, Eight-parameter datum transformation

https://forums.autodesk.com/t5/autocad-civil-3d-forum/local-coordin...

https://us.search.yahoo.com/yhs/search?hspart=blp&hsimp=yhs-def...

http://www.eng-tips.com/viewthread.cfm?qid=271665

http://www.wittwer.nl/wp-content/uploads/2009/08/cartrans.pdf

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