Why shouldn't you model in negative coordinates?

[Marcus.Isacsson]

Hi fellas!

We've always modelled in positive coordinates and have told others to do so as well (upper right corner from base point). 

But now we started wondering, WHY? Any reasons behind the practice?
What kind of problems could follow if you model downwards and left of the base point? (as another consultant has started doing in our project)

[Ilic.Andrej]

This is just one example- how our team works:

In our company template, few basic floor plan views & all shadow diagrams are already on sheets. So, we set things to minimize the first work stage. Once we import CAD survey, it lands "origin to origin" and it just so happens that it always lands at the center of the view & sheet. Often this way, there is no need to change the crop regions or add scope boxes (at least for housing). So to be centered, the origin in the CAD file is at the center of the drawing. It has both positive and negative coordinates.

So in Revit, everything has negative and positive coordinates from the internal origin. But then, we unclip the project base point and move it at the lower left corner of the building. The coordinates based on pr. base point are positive. But even if they were negative, I don't see how that would make any problems.

[Marcus.Isacsson]

@Ilic.Andrej I think that having negative coordinates can mess up calculations and things like that for other consultants when importing and modeling, but I've only heard this from others, I'm not 100% sure myself. 

[Ilic.Andrej]

Well, we never had any such problems.

[loboarch]

I can say 100% Revit does not care if coordinates have negative values. I suspect the desire to keep things in the "positive" area, is more of a human thing. For me it is just naturally easier to deal with positive numbers, easier to do the math in my head, easier to relate one point to another in my head. Revit does not really care a number is a number to is negative or positive. To people however all numbers may not be created equal (intellectually speaking).

[barthbradley]

"Negative directions" can affect element behavior.  

http://bimextension.com/revit-families-hosted-to-reference-planes-are-upside-down/

 https://www.redcage.ca/blog/directional-properties-reference-planes-revit/

[dgorsman]

Traditionally this was for a couple of reasons.  The math is easier if everything is "positive".  Drafting is a bit faster when you never have to put a "-" in front of any numbers, and it means you never have to put a "+" in front of any number for clarity either.  It also reduces errors on drawing production and reading - it's entirely possible for that "-" to disappear (missed by the drafter, or missing under a coffee stain, weld spatter, or dead pixel) which can have some... "interesting"... consequences later on.

[Marcus.Isacsson]

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@dgorsman wrote:

Traditionally this was for a couple of reasons.  The math is easier if everything is "positive".  Drafting is a bit faster when you never have to put a "-" in front of any numbers, and it means you never have to put a "+" in front of any number for clarity either.  It also reduces errors on drawing production and reading - it's entirely possible for that "-" to disappear (missed by the drafter, or missing under a coffee stain, weld spatter, or dead pixel) which can have some... "interesting"... consequences later on.

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Interesting. But for BIM collaboration, does it really matter if Revit models are made in only +coordinates or not?
Does it have a negative impact in other softwares?

[Marcus.Isacsson]

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@barthbradley wrote:

"Negative directions" can affect element behavior.  

http://bimextension.com/revit-families-hosted-to-reference-planes-are-upside-down/

 https://www.redcage.ca/blog/directional-properties-reference-planes-revit/

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Didn't know that. Thanks for sharing. But this doesn't have anything to do with negative coordinates right? (Revit model meing made to the lower left of project base point instead of upper right corner). Or does it?

[ToanDN]

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@Marcus.Isacsson wrote:

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(Revit model meing made to the lower left of project base point instead of upper right corner). Or does it?

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I have projects where the PBP is top right and there are no issues aside.  People don't like negative coordinates because the brains are generally wired to deal with positive numbers.  Computer programs don't care.

[Marcus.Isacsson]

"Computer programs don't care"

Are you sure this is the case? No problems for any other consultant?
If so, then I guess we shouldn't care and make a fuzz about it. 

[ToanDN]

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@Marcus.Isacsson wrote:

"Computer programs don't care"

Are you sure this is the case? No problems for any other consultant?
If so, then I guess we shouldn't care and make a fuzz about it. 

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No consultants of those projects have had any issues, and most of them don't care.  We use shared coordinates so they don't even need to know where the PBP is.  And none layout their design by entering the absolute XYZ coordinates like in AutoCAD.

As for my statement about computer programs, positive or negative numbers are just different binary codes, so I don't see why any programs have issues with them.

With that said, if you are a BIM manager you have the full right to dictate to always have the PDP bottom left as the convention.

[barthbradley]

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@Marcus.Isacsson wrote:

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@barthbradley wrote:

"Negative directions" can affect element behavior.  

http://bimextension.com/revit-families-hosted-to-reference-planes-are-upside-down/

 https://www.redcage.ca/blog/directional-properties-reference-planes-revit/

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Didn't know that. Thanks for sharing. But this doesn't have anything to do with negative coordinates right? (Revit model meing made to the lower left of project base point instead of upper right corner). Or does it?

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I have no idea if it has anything to do with the origin of the belief that one should only draw lines in a “positive coordinate” direction.  I only offer it up as a possible logical explanation of how and why that directive might have come about.  It could be nothing more than silly superstition, like knowing it is bad luck to pick up a penny that is facing heads down. But, in 25-plus years of Computer-Aided Drafting, I have never heard of such a thing.   

[dgorsman]

Most of the problems are from the meatware, not the software.  For example, someone jots down a set of coordinates and skips the (-), or they're working off a smudged photocopy of a half-size print; now it's a positive and a set of piles are physically in the wrong location (and yeah - such things do happen).  By keeping everything positive, there is zero chance of that type of error happening.