3D Topographical Surveys

Digital surveys are carried out using a Leica Robotic total station to either local grid and datum or more normally to OS grid and datum. If there a good mobile phone signal available it allows accurate, (RTK) real-time, fixes. If no mobile phone signal is available the same survey can be done in either of two ways;

  1. To OS grid which entails more post-processing using Smart Rinex to obtain the same positional accuracy.

  2. To an arbitrary local grid and datum, normally with fixed reference points.

Planners often require information on buildings adjacent to any proposed development and ridge heights, approximate floor levels and many other details may be picked up reflectorlessly as explained below in "Reflectorless Face Profiling"

Typical positional accuracy of the survey is normally in the order of 2cm with dimensional accuracy of the survey points in the order of 1cm or less.

Any type of terrain can be catered for and the time taken, and therefore the cost, in any particular location is dependant on the size and frequency of obstacles eg, uneven ground, buildings, trees, hedges etc. since the main criteria is a clear line of sight. All points are recorded as three dimensional co-ordinates and are coded on site so details such as road edges, footpaths and hedges etc. appear as lines rather than just dots.

Hydrographic surveys can also be carried out on inland and inshore waterways, rivers etc. The information obtained can be forwarded to specialised consultants for flood analysis purposes.

Resultant co-ordinate spread-sheets, CAD or DXF (2D and 3D) drawings can be sent electronically to your Architect, Consulting Engineer or Planning Consultant and many clients request drawings which can be printed in colour to any scale in sizes up to A1. PDF versions of the same drawings can be sent electronically but are not as clear as those printed directly from CAD.


 
 

UAV Surveys

Due to start in the next few weeks we have invested in a Sensefly Ebee aerial camera system with associated software and a small quadcopter with mounted camera.

The Ebee is an autonomous fixed wing 'drone' which when launched flies a predetermined route taking thousands of high definition photographs. Because of the overlap of images taken from differing positions the software is capable of building a georeferenced photo-realistic 3D image which can also be imported into the ground modelling software which then produces contoured drawings virtually identical to those resulting from the more traditional ways.

The accuracy of the drawings is slightly less (2 to 4cm) than with traditional techniques but the big advantage is the total coverage of the ground, the photo realism and the speed at which this can be achieved in the field. Any areas identified as requiring better accuracy can be subsequently surveyed using one of the other techniques.

The smaller quadcopter is used to capture images that are obscured to the higher flying ebee. As long as there is sufficient overlap in the photos produced the data can be used to add detail to the images produced from the ebee alone. This is particularly useful under tree cover or between adjacent buildings and can be used to give accurate models of buildings for example.

This UAV has to be piloted and can send a live video feed to the operator. It can be used on its own for inspecting and recording details where access would otherwise be either difficult or expensive such as the roofs of tall buildings, masts etc.

The combined use of both UAV's and the associated software can result in point cloud data and also 'rendered' models that are accurately referenced to the OS grid and datum. The data produced can be exported to other organisations in many different formats. The principle uses envisaged would be to cover large areas of terrain useful for developers of hydro or wind farm installations.

We are expecting to pass through the BNUC-S test with EuroUSC and gain a permission for aerial work with the Civil Aviation Authority in the next few weeks and we will be posting some of the results from our efforts as soon as they are available.

If any interested parties would like to discuss their future requirements we would be happy for any contact.


GPS Surveys

GPS surveys are carried out using a Leica GPS rover to OS grid and datum.

As above the presence of a good mobile phone signal allows for accurate, real-time, survey data (RTK). If no mobile phone signal is available the same survey can be done but entails more post-processing using Smart Rinex to obtain the same positional accuracy

Resultant co-ordinate spread-sheets, CAD or DXF (2D and 3D) drawings can be sent electronically to your Architect, Consulting Engineer or Planning Consultant and printed in colour to any scale in sizes up to A1.

Any type of terrain can be catered for and the time taken in any particular location is dependant on having a clear view of the sky.

All points are recorded as three dimensional co-ordinates and are coded on site so details such as road edges, footpaths and hedges etc. appear as lines rather than just dots. Adjacent trees or buildings can disrupt the GPS signal and may entail the use of the Total Station as above if signal disruption is encountered.


Digital Terrain Modelling

Once the survey data is downloaded and post-processed a 3D digital computer model is created using specialised software (n4ce from appsincadd) and is used to produce contour lines, normally at 0.5m spacing, but other spacing can be catered for.

This Digital Model can then be manipulated to show proposed road alignments and excavated level platforms for houses for example. Arial photographs can be merged with the 3D computer model to give Clients a detailed "birds eye view" of their surveyed ground.

Clients are able to view the 3D computer model by downloading a free viewer from the apps in cadd website here.


Section and Volume Analysis

The digital model can then be further used to produce cross sections for planning purposes or visibility splays for example. Either an unaltered or manipulated digital terrain model can be used to give volume data to allow informed decisions to be made on earthworks proposals.

Two or more digital models can be compared to give volume data eg before and after excavation or quarrying operations. Another use is providing data for Flood Analysis purposes where specialist consultants can use the model to predict flood levels, often in conjunction with Hydrographic Surveys.


Reflectorless Face Profiling

The Leica total station can be used in reflectorless mode up to a maximum of 300m to pick up survey data remotely.

This is particularly useful in places where access is difficult or impractical. One example of this is quarry faces where the data can be used to design quarry operations and calculate volumes and tonnages. Another example is building facades (interior as well as exterior), either within the area of the survey or across boundary fences or rivers. The height and position of overhead cables can also be recorded without the danger associated with traditional methods.

Planners often require information on buildings adjacent to any proposed development and ridge heights, approximate floor levels and many other details may also be picked up using this technique. A small number of points may be measured in this way in any of the two first categories if the terrain demands it.

We do not have scanning equipment ourselves (due to the limited demand) to enable "data cloud" reflectorless surveys but equipment may be available on further enquiry. They are ideal for quarry faces and buildings prior to renovation but are of limited value for terrain surveys as they pick up the top of bracken and bushes and not the ground form below.


Construction Setting Out

Setting out point data can be extracted from Architects or Consultants CAD drawings and loaded directly into the Total Station. These points can then be accurately set-out for buildings and roads, for example, in three dimensions if required. Buildings can be set out "square" from anywhere with easy sight of the instrument.

Points that have been set-out can be recorded to give proof of positional accuracy.


Title Boundary Positioning

A common area of dispute between neighbours can be the position of title boundaries since they don't always coincide with existing fences.

If a copy of the title deed is available then boundaries can normally be positioned accurately using either the Leica total station or Rover but it is dependant on the quality of the title itself and positional accuracy of fixed landmarks as most titles do not have accurate OS grid data.


Title Deed Surveys

If new housing plots are to be laid out then accurate title surveys are required before sales can proceed. During some house sales the accuracy of "adopted" boundaries are questioned and sometimes titles need to be amended to allow the sale to proceed.

The Register of Scotland are duty bound to accept data from the OS but new plot boundaries will not be shown on OS drawings and their guide-lines require sizes to be accurate to 0.1m. The dimensions need to be taken horizontally so sloping sites are difficult to measure accurately using traditional methods, diagonal sizes are also required which would be difficult to measure if a house were built in the centre of a plot.


Computer Aided Design.

The CAD drawings produced from the Digital Terrain Model can be used for example to design and show proposed road alignment and gradients or building positions to allow consents from Roads Dept and Planning authorities. Architectural cross-sections, elevations and details can also be produced.
 
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