GIS ? 1

[esass13]

I need to tie a plat to the NC Grid, which is now NAD83 I believe. The old recorded plat I have was surveyed in 1976 with no Grid reference.

The only thing I see that may be related is this:
e/c = 1/4,047

Does anyone know what this means and how to tie this plat to the NC Grid?

Thanks!

 

[jdonville]

esass13,

You can use several tools to convert horizontal and vertical coordinates between datums. Try Corpscon 6, or Global Mapper (both have free versions)

Most likely, the plat you have is recorded in survey feet - as opposed to international feet, although you might want to check with the surveyor if possible. Given the date, it probably uses NAD26 as the vertical datum.

Second, you can get approximate coordinates using digital orthophotos. Many counties have GIS websites that show approximate property boundaries as overlays to the aerial imagery and will permit you to find the approximate locations of the vertices, although you will probably need to convert from UTM coordinates to State Plane coordinates. Global Mapper will download Terraserver images and can rectify bitmaps (this last requires the full version - about $250.00 - if you want to save the rectified image).

I use these tools to help me locate boring locations using GPS.

Hope this helps.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

 

[LHA]

Jeff has it right, as far as tying an existing plat down.

Before you do this, realize that to record your new plans, they must be sealed by a Surveyor, not an Engineer. The Surveyor definitely already knows how to do this, and since you have to pay him/her anyway, I would just kick the whole thing over to the surveyor, rather than teaching yourself how to do it.

BUT, before you do anything; to the other part of your question:

e/c = 1/4,047 Does anyone know what this means

E/C means "Error of Closure", also called "Misclosure" and 1/x,000 is an unacceptably high ratio. Using modern methods (ie, computers and satalites), 1/x00,000 and even 1/x,000,000 are commonly accepted traverse adjustments. So, I would not use the plat you have as a basemap for future work. I am certain no licensed Surveyor will either.

Remember, amateurs built the ark...professionals built the Titanic. -Steve