Author Topic: Setting a common project origin  (Read 4250 times)

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JCappiello

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Setting a common project origin
« on: January 09, 2008, 03:17:42 PM »
I have a client who has asked us (not the architect) to determine a project origin for the cad files.

I'm just looking for a "rule of thumb", or a reference document which would explain the criteria for selecting the best point.  I understand the benefits of standardizing the location of the origin of a set of drawings to easily coordinate reference files.

My quandry (ok, how many times do you get to use this word?) is justifying to the client why I chose the south west corner column line intersection (that's typically where I've seen it in past projects... but that is not always the case).

The building itself will reference a site origin, but everything inside the building will reference a plant origin.

deegeecees

  • Guest
Re: Setting a common project origin
« Reply #1 on: January 09, 2008, 03:24:05 PM »
Typically, datum is originated at the bottom left (SW) from my experiences, but as they say, "Mileage may vary".

BTW, I use quandry a lot, and FWIW, theSwamp spell chacker dont no wut it is.

Cathy

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Re: Setting a common project origin
« Reply #2 on: January 09, 2008, 03:24:31 PM »
Makes sense to me...SW corner means that most of the coordinates will be positive numbers.  

Edited to add:  does it know what quandary is?  ; - )

Josh Nieman

  • Guest
Re: Setting a common project origin
« Reply #3 on: January 09, 2008, 04:01:05 PM »
We tend to take the SW corner and call it N1000.00' E1000.00' unless we have actual coords from a survey.  That or we take a solid, reliable, stationary, static, (can't emphasize the importance of not picking a point that can be destroyed or moved easily which is a newbie lesson, I know, but I'm a site plan newbie) and call it N1000',+E1000'

That was we always deal with positive numbers, even if, by chance we have to go back to the left of below the datum point (assuming north is up the page)

We don't always pick a column line or whatever, like that... unless we have -no- site data, in which case, we'll take column line intersection A1 and call it N1000,E1000.

It's worked out quite well for us so far in projects both large (large for us) and small.

Dinosaur

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Re: Setting a common project origin
« Reply #4 on: January 09, 2008, 04:20:01 PM »
Excellent advice Josh . . . one suggestion I might add:

For some insane reason, AutoCAD reports coordinates as Easting / Northing while most reasonable people  :angel: (civil types anyway) read them as Northing / Easting.  I give an additional offset (ie 1000,5000 to the coordinates to eliminate confusion or send up a red flag when someone asks me the coordinate for a point.

David Hall

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Re: Setting a common project origin
« Reply #5 on: January 10, 2008, 10:35:10 AM »
is that because Acad uses east as 0 degrees, and what does it do if you reset 0 to be north?  Would it then report back as northing/easting?
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sinc

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Re: Setting a common project origin
« Reply #6 on: January 10, 2008, 10:43:52 AM »
No, it's just because Autocad displays coordinates as XY coordinates with X first, and the X direction is the same thing as the Easting.

It works out for people in other parts of the world such as Australia, where I hear it is customary to list the Easting first.

CaddmannQ

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Re: Setting a common project origin
« Reply #7 on: January 10, 2008, 10:51:22 AM »
Hey, the best origin depends on the geometry. Sure for a more-or-less rectangular building I'd start from the lower left, really because it's just a mathamatical convention.

On a highly irregular building, I might have several connected but independant coordinate systems, and 0,0 for the main one would be at the most "regular" spot. It could be on the upper right if, say, that was the only 90o corner on the building.

But say the building was a regular polygon. I'd use a radial system with 0,0 at the geometric center.

Or perhaps it has an odd shape, but has bilateral symmetry. I'd set one zero line along the symmetrical axis and go both ways.

Then again, I'm not a surveyor. That stuff might drive them nuts.  :evil:

Dinosaur

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Re: Setting a common project origin
« Reply #8 on: January 10, 2008, 10:59:12 AM »
I tried setting 0 to north once and it raised the devil with all sorts of things.  Actually ACAD is reporting X and Y coordinates at the command line rather than north / south a subtle difference in most cases but I think resetting 0 to north could really mess with a lot of civil routines with the correction already built in.