Levels Above Ordnance Datum with RTC360

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SPharmer
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Levels Above Ordnance Datum with RTC360

Post by SPharmer » Fri Nov 01, 2019 12:50 pm

Hi everyone. First time poster here, please be gentle 🙂

I want to start off this query by saying that I am by no means a professional surveyor! I’m a draughtsman/detailer by trade but I’ve been helping a friend with various projects by measuring up and drawing building elevations. Level of accuracy isn’t particularly onerous. I used to do it by counting bricks in the good old days. Then I got more savvy and started using the BLK360 with Recap Pro to bring a point cloud into Revit. I’ve been doing that for a couple of years now.

He’s asked me to do some more buildings for him only this time, his architect has requested levels above ordnance datum on the drawings. I’ve never done this before and it’s daunting 😂 I’ve done my research and understand that the Leica RTC360 has built in GNSS which is what I need for this? So I’m arranging a hire for one of those.

I don’t suppose anybody has a link to a tutorial or a step by step guide explaining how this works and what I need to do to go from arriving on site to having the Ordnance Datum level in my Revit model?

I would be eternally grateful if you do! Thanks all.

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Re: Levels Above Ordnance Datum with RTC360

Post by Phil Marsh » Fri Nov 01, 2019 2:10 pm

Hi Steve,

Welcome to the forum.

How accurate do you require the levels to OS to be?
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Re: Levels Above Ordnance Datum with RTC360

Post by SPharmer » Fri Nov 01, 2019 2:18 pm

Phil Marsh wrote:
Fri Nov 01, 2019 2:10 pm
Hi Steve,

Welcome to the forum.

How accurate do you require the levels to OS to be?
Hi Phil, I’d ideally like to get them as accurate as I can but it doesn’t necessarily have to spot on to the mm. what sort of tolerance do you think I’d be able to achieve just using a RTC360?

Thanks!

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Re: Levels Above Ordnance Datum with RTC360

Post by Phil Marsh » Fri Nov 01, 2019 3:13 pm

You are aware this will not export the data as per the GNSS positioning - it's purely a visual overlay to align the images and the scan data. You still need to apply external control to move it to a grid of your choice.

I would recommend hiring something like a smart net rover which is easy to use and will get the survey to OS within a few millimetres.


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Re: Levels Above Ordnance Datum with RTC360

Post by James Hall » Fri Nov 01, 2019 3:51 pm

Hello Stephen,

We are separated by more then a common language and some water. The step by step instruction of how to get your assumed coordinate / Local grid translated and rotated to a ordnance datum is not hard. The problem arises of legal and professional liability.

The issue is intended use and if you need certified data to said datum.
A surveyor could run a control loop that you could then scan targets on top of for the control points, this would Geo-reference your scan.
If the Building scan is being used for Green building modeling and the orientation and coordinates of the data dose not need to be crazy accurate.

So why dose it need to be on Datum?
Is it for Floor Elevation?
Is it for reference in to other programs?
You need to know.
As a draftsman / detailer you are better served by getting a professional to get you some common points you can then scan on top of.
In America if this went sideways people would sue sue sue. The money spent on a professional for a control servery is cheep insurance.
With the UK I don't know what is prudent, others can advise you better.

James,

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Re: Levels Above Ordnance Datum with RTC360

Post by mike annear » Wed Nov 06, 2019 5:51 am

I agree with James,
If your client has asked for the data on ordnance coordinates it must be for a reason.
The other good reason to hire a trained surveyor is that you can use their coordinated targets to correct any levelling mistakes that the RTC360 might introduce as it doesn't have a survey grade compensator
You can also use the surveyed targets to check your registration.
Regards,
Mike.

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