laser surveys · sketchup (skp) the functionality of the model will depend on format in which the...

Laser Surveys BIM ready models

© P a g e | 1

LASER SURVEYS

BIM Ready Models

A guide for our Clients


© P a g e | 2

Introduction - the purpose of this guide:

Survey information for the construction industry has a long-established

tradition and is generally well understood by both Clients and Surveyors.

The advent of BIM has led to presenting information in different formats

and this document attempts to clarify what can, and cannot, be delivered.

With an understanding of what is intended to be issued, a Client can adjust

their order to ensure that the model will meet their needs.

The Company: Laser Surveys was established in the Midlands in 1975 with our London office

opening in 1988. We carry out all types of survey work throughout the

mainland UK with our team of over 60 employees.

Our Services: Topographical surveys, building surveys and underground services surveys

are just part of what we do.

We also supply digital datasets and reports, OS mapping, 3D Models, UAV

surveys, historical mapping, geological and borehole information, and we

have been providing BIM ready models since 2015.

Experience: Over forty years of providing surveys using the latest surveying techniques.

BIM Team: We have a team of dedicated Revit modellers in both our London and

Worcester offices, allowing the size of the project team to be expanded to

suit the workload.


© P a g e | 3

Essential information for creating a BIM ready model:

To meet our client’s requirements we need to understand the

following:

1. Which “Grade of Detail” of the Revit Model is required for the site,

the building exterior and the building interior.

If you want Phasing applied to the model.

2. If any 2D CAD drawings are also required.

3. If the Point Cloud data is required.

4. If the Survey is to be located on a local Datum and Grid or to the

OS Datum and National Grid coordinate system.

And as a Client you should also be aware of:

5. That the extent of the model is dependent upon the access that

the surveyors are given.

These items are identified on the “Revit Deliverables” part of our order

form where our clients can select options and add comments or specific

requirements.

Each of these items is explained in more detail in the following sections.


© P a g e | 4

1a-buildings GRADES OF DETAIL FOR BUILDINGS AND STRUCTURES

Our simplified order form has four “Grades of Detail” for

buildings and structures.

GRADE B4 – High Detail.

Laser Surveys project specific families of doors, windows, stairs, ramps

and balustrades.

Project specific families based upon more detailed dimensions for

fixtures, fittings, materials and architectural features.

GRADE B3 – Standard Detail.

Laser Surveys generic families of doors, windows, stairs, ramps and

balustrades.

Generic families based upon overall dimensions for fixtures, fittings, and

architectural features.

GRADE B2 – Outline Model.

Overall shape of major walls, columns, floors, ceilings and roofs, with

openings.

GRADE B1 – Massing Model.

Overall shape of external building envelope.


© P a g e | 5

ITEMS TO CONSIDER FOR GRADES OF DETAIL FOR

BUILDINGS AND STRUCTURES

Different “grades of detail” can be applied to the interior and the exterior,

or to different buildings, or parts of buildings on the site.

For example, on a refurbishment project the model may require a high

grade of detail (B4) for the exterior, which is to be retained, but only an

outline grade (B2) for the interior, which is to be stripped out.

Consideration for grades B2, B3 and B4 should be identified for:

• Walls

• Cornices

• Dados

• Skirtings

• Floors

• Structural Columns and Beams

• Secondary Structural elements

• Ceilings and ceiling features

• Bulkheads

• Roofs, gutters and fascia’s

• Windows and Curtain walling

• Doors and screens

• Stairs and handrailing

• Lifts and escalators

• Fixed furniture and fire surrounds

• Pipework and sanitaryware

• Building services

Please identify on the order form if extra detailing to any of these is

required.

Where no specific requirements are identified for these then Laser Surveys

standard modelling techniques will be used.

A Revit phase of “Existing” can be applied. We do not normally do this

unless a Client requests it. Phasing can make items appear, disappear and

change colour, so unless it is used on a project we do not normally apply it.

Often it is only practical to survey one side of an element (for example a

ceiling) but a thickness is required to create an object in Revit.

Where this is necessary the object properties will be named

“Wall/Floor/Ceiling/Roof of unknown thickness”.

Laser Surveys generic families are created in accordance with NBS BIM

Object Standards in terms of geometry, behaviour and presentation.

Metadata within the Laser Surveys generic families is compliant with the

requirements for generic objects as specified within the BIM Object

Standards.

Clients can thus add in their own metadata, as information becomes

available during the project, and the survey model would comply with the

requirements for a COBie data drop.


© P a g e | 6

1b-site GRADES OF DETAIL FOR TOPOGRAPHY

The order form has a further three “Grades of Detail” for Site

Topography.

GRADE S3 – Revit Toposurface with sub-regions and site

features.

Revit “toposurface” based on site level data points, and then divided into

sub-regions to identify surface finishes.

Site features such as steps, street furniture, barriers, retaining walls, and

trees also modelled as Revit objects.

GRADE S2 – Revit Toposurface with sub-regions

Revit “toposurface” based on site level data points, and then divided into

sub-regions to identify surface finishes.

GRADE S1 – Revit Toposurface only

Revit “toposurface” based on site level data points.


© P a g e | 7

ITEMS TO CONSIDER FOR GRADES OF DETAIL FOR SITES

AND TOPOGRAPHY

Different grades can be applied to distinct parts of the site, for example

stairs and ramps directly connected to a building may be required.

Revit “toposurfaces” do not happily run vertically or fold back on

themselves. It is often better to split surfaces at the top and bottom of

kerbs.

If this is not done, then Revit tries to join alternate top and bottom points

giving a diamond shape to the edges. Kerbs are not modelled as Revit

objects.

Revit representations of trees and bushes are generic and only represent

the approximate overall position, height and spread. The Point Cloud should

be used as a data source for more exact geometry of such items.

OTHER MODEL OUTPUT FORMATS –

AUTOCAD, IFC, MICROSTATION and SKETCHUP

3D models can by issued in a variety of formats including:

Revit (RVT and RFA)

AutoCAD 3D files (DWG)

IFC files (for use with Vectorworks etc.)

Microstation (DGN)

SketchUp (SKP)

The functionality of the model will depend on format in which the model is

issued.

RIGHTS OF LIGHT SURVEYS

We regularly carry out “Rights of Light” surveys of specialist consultants

where large areas are surveyed, in outline form, with door and window

openings.

These are far more accurate than the off the shelf data that is sometimes

(but should not be) used.

We can also produce this information with “polylines” around all openings

allowing it to be used in the specialist analytical software used by “Rights

of Light” Surveyors.


© P a g e | 8

1c-above ground services GRADES OF DETAIL FOR ABOVE GROUND SERVICES

We currently offer only one “grade of detail” for above ground

services.

GRADE A2 – Services geometry modelled

We will only model the overall size (including insulation) and position of

above ground services, which will not contain the intelligent information

usually incorporated into a BIM object.

Support brackets and structures can be modelled, and generic valves and

fittings can be included.


© P a g e | 9

1d-below ground services GRADES OF DETAIL FOR BELOW GROUND SERVICS

We offer only one “grade of detail” for below ground services

GRADE B2 – Services geometry modelled

We will only model the approximate overall size and position of below

ground services, which will not contain the intelligent information usually

incorporated into a BIM object.

Models include a “zone of uncertainty” which represents the limitation of

accuracy of the detection equipment. Some assumptions are also made in

order to make Revit objects, such as the thicknesses of buried walls and

slabs.

Not all underground services are detectable from surface scans. Modelling

them in Revit does not improve the accuracy of what was surveyed with

detection equipment.

Where underground services are accessible we do offer a surveying and

scanning service. Our surveyors have confined space training and we can

arrange traffic management and escape teams for such works.


© P a g e | 10

2-CAD output IN ADDITION TO THE REVIT MODEL WE CAN ALSO OFFER 2D

CAD DRAWINGS IN DWG & DXF FORMATS

2D CAD 1:100

We can produce traditionally annotated 2D plans, ceiling plans, sections and

elevations from the model for an additional cost. The annotation will

include figured dimensions for ceiling heights, floor levels, window cill and

head heights and door head heights. Beams and ceiling features will be

shown as dotted lines.

A client’s linestyles and layering conventions can also be incorporated.

Unannotated plans, sections and elevations can also be created at no extra

cost.


© P a g e | 11

3-point clouds THE ORIGINAL POINT CLOUD CAN BE SUPPLIED

-OR ACCESS TO IT OVER AN INTERNET CONNECTION

There are three options for including the Point Cloud as a Deliverable.

This needs to be identified before the surveyor’s visit site as it will affect

the methodology used in the survey. Full colour point clouds add

considerably to the amount of time spent on site, and consequently the cost

of the survey.

Point Cloud Options

Black & White

Supplied in AutoDesk Recap (RCS), Bentley MicroStation (POD) or E57

formats, usually via a Dropbox link.

For exceptionally large files we issue point clouds on a memory stick for a

small additional charge.

Colour

Supplied in AutoDesk Recap (RCS), Bentley MicroStation (POD) or E57

formats, usually via a Dropbox link.

For exceptionally large files we issue point clouds on a memory stick for a

small additional charge.

Colour point clouds are more expensive but easier to interpret.

Areas without lighting (such as loft spaces) must be scanned in black and

white to obtain any detail. Applying colour to such spaces will result in a

very dark or black point cloud.

Webshare

We can also host the point cloud data and give clients access to it from their

phones, tablets or PC’s.

Users can inspect the survey, move around it and take levels and dimensions

to any point.

The advantage of this is that no specialist software is needed to inspect and

interrogate the data.

An annual charge is made for hosting the data, plus there is a nominal fee

for uploading it initially.


© P a g e | 12

4-positioning WHERE COLLABORATION IS IMPORTANT, AS IT IS WITH ALL

BIM PROJECTS, A SHARED SURVEY POINT NEEDS TO BE

AGREED

A Datum, in surveying terms, refers to the vertical height (the z value) of

a point.

A Grid is established in plan view and refers to the vertical and horizontal

positions (x and y values) of a point.

Local Datum and Grid by Surveyor

Our surveyors will establish a local datum and grid point for the survey and

mark it on site and on the survey deliverables.

Construction sites do often damage or obliterate such points, so they should

not be relied upon to be there for the whole duration of the project.

Local Datum and Grid by Client

We can work from a defined point identified by Client, providing this can

be identified to the surveyor upon their first visit to site.

Ordnance Survey Datum and OS Grid.

Many projects use the OS datum and OS Grid coordinates that cover the

whole of the UK.

These are usually annotated as Northings and Eastings for example:

529990E,169990N for gridlines or E384581.299, N255359.262 for individual

points.

Benchmarks are no longer verified or checked by the Ordnance Survey and

are therefore rarely used as they may have moved. We use a satellite system

to establish both Datum and Grid.

Hybrid systems are also available e.g. an OS Datum can be used with a local

Grid. We can accommodate these if we know our Clients requirements

before we commence the survey works.


© P a g e | 13

Revit “True North” and “Project North”.

Revit has way of rotating a model without actually rotating it !

It has options for displaying “Project North” and “True North”.

True North in our models will depend upon which “Positioning” option has

been selected earlier in this section, i.e.” Local datum and grid by

surveyor”, “Local datum and grid by client” or “OS datum and OS grid”.

Revit “True North” will align with the survey, which will align with

whichever of those options has been chosen.

Revit “Project North” can apparently rotate the model. This is useful where

buildings are slightly askew, either to the vertical or horizontal planes. It

can be apparently rotated, making drawing new walls much simpler.

Rotating “Project North” does not alter the underlying coordinate system,

which will still read correctly.

It is important to establish this before modelling commences as moving or

rotating a model afterwards, although not impossible, can be problematic.

Please be aware that selecting “True North” in Revit will only orientate

your view to OS North if you have told us that that is the way you wanted

site surveyed, i.e.” OS Datum and OS Grid”.

We include this on our order form and if left unanswered take the view that

Revit “Project North” will be decided by the Surveyor, unless it has

previously agreed with the Client or the Clients Architect.

Using large coordinates

Revit has problems with large coordinate numbers, but our surveys can be

set up to OS Datum and Grid and other Revit files can then simply “Acquire”

the coordinates from our survey.


© P a g e | 14

Other Positioning Issues

Repositioning a model after completion can be problematic as the point

cloud and model are set to the same coordinate system before modelling

commences.

Projects are often initiated with an OS Mastermap plan or Title Deed

information from the Land Registry. The latter relies on the former for its

information, and the “absolute accuracy” of an OS Mastermap is:

Scale RMSE* 95%

confidence

level

99%

confidence

level

1:1250 (urban) <±0.5m <±0.8m <±0.9m

1:2500 (rural) (resurvey or reformed) <±1.1m <±1.9m <±2.4m

1:2500 (rural) <±2.8m <±4.7m <±5.8m

1:10 000 (mountain and moorland) <±4.1m <±7.1m <±8.8m

We discuss the accuracy of the survey in our “Client guide to accuracy”

document and generally achieve better than ±25mm. Deed plans and OS

maps are ±800mm in urban areas and ±1900mm in rural areas for a 95%

confidence level.

Hopefully this demonstrates the need for an accurate survey from a

company such as ourselves at as early a stage as possible in the project.

We cannot determine in law a boundary position, but we can accurately

locate certain physical features to enable legal professionals to progress

matters in the appropriate way.


© P a g e | 15

5 - access Remember – if you cannot see something from where you

are standing (such as hidden pipework, columns or

beams), it is likely that we cannot survey it.

Survey as found

The standard for most of our surveys.

Areas cleared by client prior to survey.

Existing items are removed and replaced by the client, for example ceiling

tiles, if the structural floor depth needs to be measured.

Specialist access equipment provided by client.

If surveys are needed where safe access is not normally available, for

example lift shafts, then the client may provide safe facilities to allow our

surveyors to carry out their work.

We also publish “BIM Ready Models – Client Guide to Accuracy” should you

wish to know more about the accuracy standards of our models.

If you have any questions or comments about anything in

this document, then please contact us.

This document is copyright of Laser Surveys Ltd. and may not be reproduced in any

form, in part or as a whole, without the written permission of Laser Surveys Ltd.

t: +44 (0)1886833173

e: [email protected]

Issue B – 16/04/2018

tel:044

laser surveys · sketchup (skp) the functionality of the model will depend on format in which the...

Documents