Rectified photographs

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In the absence of line drawings, rectified photographs of the elevations of a ruin can be used to identify the location and scope of defects (Figure 3.19). In general, they are more useful to superimpose survey grids onto than for annotation of defects, since the level of detail in a photograph can prevent clear identification of individual repairs; they can, however, be used to indicate the general scope of recommendations, for example locations where repair to wall heads is required or where repointing or grouting of fractures is necessary. Aerial photographs can be used in place of site plans, especially where low-level wall remnants exist.

If rectified photographic elevations exist as well as line drawings, the surveyor will benefit from using both, since the photographs will provide a visual record of the appearance of the ruin at a point in time.

Where the production of survey drawings will form part of the client brief for a condition survey, it is also useful to consider commissioning rectified photography as part of the drawing production. Rectified or stereo photography can reduce the time needed on site to obtain survey data by reducing the need to take levels and survey targets across the ruin. Scaled line drawings are then produced by tracing over the rectified photographic image, which is imported into a computer-aided design package. Greater accuracy is achieved by specialist surveying companies using stereo images that are accurately traced over using a combination of specialist machines and software.

Three-dimensional scanners have also brought significant benefits to the production of scaled line drawings and are becoming increasingly accurate and capable of identifying points in space on a 10 mm X 10 mm grid. They can also provide three-dimensional models that illustrate distortion and lean in ruins and surrounding typography, which in the right circumstances can bring valuable clarity to the condition of the ruin in the local environment. These models can also be developed to aid presentation of the site to visitors.

Where digital data is produced this should always be supplied in a format that is commonly used, such as AutoCAD.dwg format or .dxf format.

Vocabulaire Porte
Figure 3.16 Newstead Abbey West Front. An example of a condition survey drawing overlaid with grid lines to locate defects within a small, identifiable area. The plan layout of the finials has also been added to the drawing so that each grotesque sculpture can be numbered and referenced.
Survey Drawing

Figure 3.17 St Luke's Church in London. A condition survey drawing with grid lines. In this example key defects have been annotated into the drawing to convey the scope of repair. Blue shading represents areas of stonework which are well bonded to the brick structure behind. Areas of white represent voids behind the stonework which require grouting. The tower was not included in the sway of masonry voids.

Figure 3.17 St Luke's Church in London. A condition survey drawing with grid lines. In this example key defects have been annotated into the drawing to convey the scope of repair. Blue shading represents areas of stonework which are well bonded to the brick structure behind. Areas of white represent voids behind the stonework which require grouting. The tower was not included in the sway of masonry voids.

Building Seaside Drawing Dwg
Figure 3.18 Waterlow Park in London. Simple elevation drawings have been done by hand to assist in conveying the scope and nature of defects identified in the condition survey. The drawing was prepared based on basic site measurement and photographs.
Figure 3.19 Guildford Castle. Rectified photographs can be used in the absence of elevation drawings.

76 Conservation of Ruins The survey process

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