Plant North 3

[StrP88]

I know this is not a really Structural Eng. question but appreciate if anybody knows the answer.
When I go the plants, they frequently say this is the Plant "North" direction, and I wonder what is the difference between plant north and real/true north!!!

If anybody knows or encounters I appreciate for sharing it with me

Thanks

 

[cvg]

Plant north is the assumed north from the original site layout design. actual north may be different than grid north or magnetic north which may also be different than plant north.

"Grid north" is based on a state plane or national grid or some other local grid.
"actual north" is usually based on UTM projection
"magnetic north" is variable and you can establish that with a compass

In north america, the national grid would be based on the NGS datum, or state plane system

https://www.ngs.noaa.gov/faq.shtml#HorzDiff

in other countries, there are other datums, such as British National Grid (BNG)or UTM

https://pubs.usgs.gov/fs/2001/0077/report.pdf

 

[dhengr]

StrP88:
The convention of “Plant North” or “Plan North” is more or less just a drafting and orientation convenience. Grid lines were usually drawn horizontally and vertically of a drawing, and north is up. That’s the way our drafting tools worked easiest. We did not want to put a north arrow pointing 18.75̊ to the NW or NE on every drawing, because it really didn’t matter at this phase of the project. In the plant, everyone knew where the front gate or some obvious feature was so that was on the north or the south, give or take a few degrees, so this orientation and communication was the norm. The few times that “True North” was significant in a communication, on a plan, or plot plan, both would be shown. Certainly, surveyors showed both, but their work involves legal descriptions of property as well as locations of the infrastructure so they did have to tie the two orientation systems together.

 

[JStephen]

Ask and find out. It's not an unreasonable question, and lack of that information can lead to some expensive mistakes and confusion.
If you have any kind of facility that is laid out on a square grid, and that grid is oriented at some random orientation relative to true north, it is convenient to designate a plant north aligned with that grid.
On our drawings, that will be shown as "plan north".
It is common to see plan/plant north and true north confused on the drawings. IE, site plan shows where plant north is, then detail drawings show a north arrow, but it is plant north, not true north, but nothing to indicate that.
Pet peeve: getting drawings in where plant north is one random direction on the paper, true north is some other random direction on the paper, and whatever is drawn is just at some random angle. Like, they just spun the spinner to see how to orient stuff on the page.

 

[dhengr]

Jstephen:
I agree with your pet peeve, and the potential difficulty of not showing/defining the correct difference btwn. the two. My pet peeve is the way so many people give directions while describing something, a problem, a structure, a situation, etc. Over there, to the left, on the right, up there, just doesn’t cut it when I don’t know which way you are facing with each new sentence. But, N, S, E & W do not change, so one can start to develop a mental picture of what the OP’er. is trying to describe. I suspect that people are not being taught to read maps and plans any longer, if they don’t have their GPS, with screen, or CAD program, they can hardly find way to the next room.

 

[StrP88]

Thanks everybody for your kind response.
I am glad I was not getting any shout why I asked it here in this forum.

Again, appreciate everyone for your time and sharing your knowledge

Regards,
StrP88

 

[drawoh]

StrP88,

I live in Toronto, Ontario, Canada. Toronto is located at one corner sort of of Lake Ontario. It is rotated around 45[°] with respect to true north. When we refer to north, east, south, and west, we are using a local coordinate system that is rotated with respect to the outside world. If you move "west" from Toronto, everything is wrapped around Lake Ontario, and the coordinates rotate too. I have not checked, but I assume that north, east, south and west are fairly close to reality in Hamilton.

This should happen with any town or city located close to a geographical feature.

--
JHG

 

[MotorCity]

drawoh....great, now we Americans have to deal with "metric north"

 

[Settingsun]

Is there an overhead crane or some other travelling machine involved? In those cases, instructions are often given as "20cm/8 inches to east", which avoids the problem of saying "move it left" then having the operator move the crane to his/her left instead of your left.