need a sanity check - LOA and deviations

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crullier
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need a sanity check - LOA and deviations

Post by crullier »

Hello guys,

I have a couple of quick questions:

Let's say that you scan a building that you need to convert it to CAD/REVIT to provide a typical floor plans. We all know that there is software out there that will allow you to extract a slice from the point cloud and will fit linework to the point cloud and generate some sort of 2d floor plan. Some are better than others but you still need to clean up those lines, especially the corners. This workflow fits the lines to the point cloud and gives you the most "true" as-built in my opinion.

The challenge:
If you give this to an architect, they would say that that drawing is not very useful (naive in my humble opinion) and will request a CAD drawing with 90 deg angles etc. Now you are deviating from the point cloud to provide something that is closer to the "design" intent than reality. So far so good.

So here is where I need the sanity check:

1- would you charge more for an ortho design intent drawing (considering that this will take more time overall)
2- how do you ensure that you staying within your contract LOA when doing a design intent drawing. I have found that in some areas of the scan, walls were built or out of square that by providing a "straight" wall I am out 3" at the opposite end and therefore not providing the LOA I promised.
3- do you take the time to show these deviations as the rest of providing two sets of linework for large projects.

I am interested to hear how some of your handle this, especially when dealing with Revit or other BIM platforms where you are almost forced to draw all walls perpendicular and straight.

Here is a point cloud we are working with (see image attached)
A: linework fitted to cloud
B: Ortho interpretation (less accurate by nature - and more time consuming)
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crullier
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Re: need a sanity check - LOA and deviations

Post by crullier »

I also wanted to add this is one of several segments of wall that form a line along a facade. And none of them line up or align to a coming face (poor site surveying and layout)
Last edited by crullier on Wed May 05, 2021 3:37 am, edited 1 time in total.
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Re: need a sanity check - LOA and deviations

Post by VXGrid »

crullier wrote: Sun May 02, 2021 8:51 pm 1- would you charge more for an ortho design intent drawing (considering that this will take more time overall)
2- how do you ensure that you staying within your contract LOA when doing a design intent drawing. I have found that in some areas of the scan, walls were built or out of square that by providing a "straight" wall I am out 3" at the opposite end and therefore not providing the LOA I promised.
3- do you take the time to show these deviations as the rest of providing two sets of linework for large projects.
In my opinion (and I'm no expert in CAD/BIM) this is all coming down to: What did the Architect order from you, and what is he going to do with it.
If this is for rental floorplans, real estate and things like that, where you normally work with 1:100 plans, going for the 90° corners is somewhat! normal.
If this is for as-build you want to have the most accurate thing, since on your plans the planning is happening.

Generalisation (shaping edges to 90°) is okay as long as this is within the tolerance you are providing.


If you need more time & effort to produce linework with straight storybook 90° angles I don't see a mistake to charge more for that, but again, I would try to handle that in the contract before starting the work, what they want to have as an end product from you.

Aren't there automatic tools to generalise the linework?
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Re: need a sanity check - LOA and deviations

Post by Peyman Bashiri »

Well, I personally never going to use anything other than pure Recap and Auto Cad for 2D and Revit for 3D. For 2D CAD drawing you only need to narrow down the point cloud to a thin slice, set the UCS and draw the floor plan outline or facade or section.
Revit is a bit more complicated but I will never needed anything else.

Peyman
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sim.herrod
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Re: need a sanity check - LOA and deviations

Post by sim.herrod »

For as-built floor plans and elevations we always draw to the point cloud.
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Re: need a sanity check - LOA and deviations

Post by stutosney »

This is an interesting question and depends on different variables I guess.

In your proposal document for the client, you will likely have a tolerance threshold on the accuracy and will be delivering to a set scale, probably 1:100. It also depends what the plans will be used for, if it is lease plans then accuracy isn't overly important. You also have to remember, this is a 2D plan, so whilst you are drawing to the cloud at your particular slice level, depending on the verticality o the walls, your wall line could in fact be 'incorrect'. When it comes to 2D plans, I don't see a problem with averaging a slightly skew wall in order to make life easier for yourself when drafting, as long as it is within reason and within the tolerances set out in your proposal. I would also average the difference out over the length of the wall, so you have 1,5" each end as opposed to 3" on one end. You have to remember, if you weren't using a scanner, you likely would have measured the building with a tape and disto or a total station at best and doing this, you will be basing all your drafting on single points along wall faces. Scanning is more accurate and provides multiple checks along wall faces etc, but I find people can sometimes get hung up on accuracy because they have too many points. Too much information isn't always best. If you really are concerned about delivering a true building representation to your client, consider a 3D deliverable.
crullier
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Re: need a sanity check - LOA and deviations

Post by crullier »

Thank you all for the feedback and validation.
It in interesting to see the some of your model or draw to the point cloud. The "problem" that I hear with such deliverable is that some of the "old timer" architects want to draw to those textbook 90% angles under the premise that their drawing are "design intent". To which I would answer, then why go measure or scan in the first place right?

I find that many of our clients just want 2D CAD - I guess in part to keep the cost of the surveys down.
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Re: need a sanity check - LOA and deviations

Post by ScottErnst »

In the residential world, in my experience, the architects want nice square drawings because they are easier to work with. In that world an inch or two doesn't matter but it is time consuming to cut and paste things into out of square line work. I've actually had architects complain that my drawings weren't square even though the wall that was out of square would've been a foot off of the point cloud in places. If they want square drawings I just put it in the contract that the drawings will be off by a few inches in places. If there is something that's radically (but not intentionally) out of square I'll draw that the way it is. In this world we are competing with the tape measure and pencil folks, who are off by feet at times, not against surveyors.
crullier
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Re: need a sanity check - LOA and deviations

Post by crullier »

I like your last senstence. lol
I agreed with your many of your ideas. Thank you for sharing.
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Re: need a sanity check - LOA and deviations

Post by stutosney »

crullier wrote: Wed May 05, 2021 6:12 am I like your last senstence. lol
I agreed with your many of your ideas. Thank you for sharing.
It comes down to having a water tight contract to protect yourself - I wouldn't advise just going out and drawing plans square based on this conversation thread, make sure your clients are aware of what they are receiving and that it is clearly stated in the terms of the contract, or better yet, have the conversation with the client beforehand and explain that walls aren't always perfectly square, you may come to an agreement of some sort, say, you will square off any walls that are less the XXmm over XXm length or something similar.
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