Capturing Kibworth Harcourt Windmill

A 3D Digital Survey of our historic post mill creates a 'digital twin' which contains 1.74 billion colour 3D points - an important resource at every stage of our repair project. Andy Beardsley of SPAB Heritage Awards sponsor Terra Measurement, recounts the process.

Kibworth Harcourt Windmill is the last remaining post mill in Leicestershire. It is a Scheduled Ancient Monument and a Grade II* listed building. The majority of the mill dates back to 1711 or earlier and its interior is covered with the graffiti of millers who worked at the mill until the 1930s. Dendrochronological studies suggest the main post is even older and may have been in a previous mill. 

After a generous legacy was left for the mill, the SPAB started planning the repairs of the in 2019. As with any repair project like this, the important starting point is an accurate 3D Digital Survey that captures a ‘digital twin’ of the structure.  A digital twin is digital version of the real thing, in this case formed by billions of 3D spatial data points called a ‘point cloud’. This spatial data from our 3D survey provided a resource to create drawings, models, and visualisation of the windmill to enable analysis, design, and planning. 

Our 3D digital surveys are the ultimate digital documentation of visible surfaces of a building or structure.  The surveys provide essential information for analysis and preventative maintenance. In a catastrophic situation of fire or collapse, our data helps the disaster mitigation process of an accurate re-build or structural repair. 

After careful planning and installation of high accuracy survey control and targets, we began our colour 3D Laser Scan Survey.  There were 39 individual scans both inside and around the mill. The resulting point cloud digital twin data contains 1.74 billion colour 3D points. You can look at the point cloud data on of the Lower Mill, the Upper Mill, and look at Horizontal and Vertical Slices on vimeo.

After the point cloud spatial data was processed, we manually traced the drawings required in AutoCAD. These 2D drawings were Floor Plans on 3 levels, External Elevations showing the weather boards, Internal Elevations showing the wooden frame and structure and Section slices at key positions to inform the project team. 

After the project team’s initial appraisal process, we were then asked to produce an accurate 3D model of the timber structure. We created this in Revit, and it was used to assess the structure and calculate its ability to bear the new loads of new sails, tail pole and roof. 

The repair work began in August 2021 and was completed earlier this year by millwrights Dorothea Restoration.