Surveying for Architects

As a general rule-of-thumb, the following accuracies can be expected from the technologies Landair utilizes: Stationary (static) laser scanner: up to +/- 3-5mm Mobile laser scanner: up to +/- 10-15mm Survey total station: +/- 3mm Survey-grade GNSS (GPS): +/-20mm RPA (drone): Horizontal +/- 20-50mm; Vertical +/- 150mm (largely dependent on surface reflectiveness, object contrast and consistent topography) Survey-grade dumpy level: Vertical +/- 1mm

Stationary, or static, scanners (Landair uses Faro Focus S150+ scanners) are set up on a tripod at each critical location and moved around the scene between scans. Scanning times at each location range between 2min and 10min depending on site constraints. Mobile scanners (Landair uses the wearable NavVis VLX3 scanner) run continuously as the surveyor walks through the scene capturing everything it sees on-the-fly. Stationary scanners are more accurate, but the trade-off is the time spent on site. Mobile scanners allow quick measurement of a scene, but the trade-off is a slightly lower accuracy compared to stationary scanners. There are also different pointcloud formats, densities and ranges between the two scanning types. Please consult Landair’s 3D Laser Scanning Options for more details. 3D Laser Scanning Options.pdf

It varies project to project. While both include the foundational elements of walls, windows, doors, ceilings, columns, stairs, fences, etc., LOD400 includes the finer details like ceiling objects, wall fixtures, electrical equipment, rigid ducting, etc. Please consult Landair’s LOD Options as a guide for what’s included / excluded for the different levels. LOD options.pdf

Revit is predominantly a design platform. As such, it assumes straight walls, flat floors, consistent gradients, etc. Laser scanning, though, records buildings or infrastructure as-is, walls not perfectly square, floors not perfectly flat, etc. When a model is created in Revit from a pointcloud it is effectively dumbed-down to fit Revit’s design constraints. As such, a lowering of accuracy is inevitable. From experience, it’s not unusual to find differences of up to +/-20mm between objects in the 3D model and the corresponding points in the 3D pointcloud.

Landair Surveys is covered by $20,000,000 Public Liability Insurance and $10,000,000 Professional Indemnity.

We do. Landair utilises the Cintoo web-hosting platform to create online viewers. Cintoo allows specified users to take virtual walkthroughs of the laser scanning data. You can view in image mode (like Google Streetview) or in 3D surface mode and take ad-hoc measurements as required. Viewer access can be password protected for added security. Most laser scanning quotes will include a nominal access period to Cintoo as a free value-add to our client. If useful, additional hosting time can be purchased based on the number of scans taken.

How long is a piece of string? Most of our field work for architects is completed within a day but major projects can be spread over a week depending on the complexities involved. The largest scanning job Landair has completed to date had the fieldwork spread over four weeks due to site constraints. For smaller jobs, the required plans are usually completed within a few business days following the fieldwork. Larger projects have a data handover usually one to two weeks following fieldwork. Major projects and high-detailed modelling jobs will usually have final data handover two to four weeks following fieldwork.

For colourised pointclouds, high-resolution imagery is taken at each scanning location and the relevant RGB value of each image pixel is assigned to the corresponding scan points. This is good for most scanning environments. However, very dark or glary environments will significantly affect camera exposure leading to washed out pointcloud colouring. In such instances it is better to scan in greyscale format. A pseudo black-and-white image is created from the laser scanner’s intensity values to allow better viewing of the pointcloud. Greyscale scanning is quicker than colour scanning due to the time spent for image capture at each scanning location. Most of Landair’s clients choose colour scanning for outdoor environments and greyscale scanning for internal environments to bring the overall scanning costs down.

You can, but you need to be aware of the limitations. Most architects will choose 3D modelling to align to LOD300 or LOD400. There are objects included in LOD400 modelling that aren’t in LOD300. For example, most wall fixtures (vents, lights, electrical equipment, decorative elements, etc) are not included in LOD300 modelling. Any façade elevation plan extracted from a LOD300 model won’t include such elements when they would probably be useful to show on a plan. The same applies to floorplans and RCPs. If the preferred final deliverables are printed plans instead of electronic models, it is often better to draft façade plans, floorplans and RCPs directly from the pointcloud. That way, all desired elements are included.

Multiple scans are often required to measure everything within a scanning survey extent. This will mean the same real-world location can be measured by three or more scans. Even with a highly-accurate scanning control network and lots of overlapping linking targets, miniscule scanner and positional errors can lead to a spread of points for each real-world position. Usually, this point spread is within +/-3mm. However, black or highly reflective objects, shallow angle measurement and long scanning distances can affect recorded laser pulse values. This inevitably leads to increased ‘noise’ in the pointcloud. When we create plans and models from the pointcloud we ignore the outliers and filter through the ‘noise’ to make sure what we provide represents what’s on site.