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5.5 Field drawings: plans

Established procedures used by the LRC include the production of field drawings on A3 sheets of drafting film at scales of 1:50, 1:20 or 1:10, as appropriate. Rather than employ a grid of drawing sheets covering areas of intensive activity, where the feature distribution is sparse, individual drawings are aligned to give the best coverage of individual features. Drawings incorporate 2-4 drawing points that are logged by Total Station, with the 3-D coordinates facilitating georeferencing. Each feature is then digitised by hand using G-Sys software and a digitising tablet with a resolution of 1000 dots per inch. Each drawing object can incorporate multiple 3-D polygons and 3-D polylines, each of which can use any available colour/layer/line-style/fill-style combination within a single structure that incorporates the context KEY_ID as the drawing name and, optionally, a sub-key and a coverage name. Rather than employ hachures, which owe much to the use of pens with flexible nibs during the 19th century, to reflect the shape of features, contours at 5cm intervals are drawn on the plans and then digitised as 3-D lines (see below). The elevation component in the 3-D digitised record is not absolute but relative, as the feature cut is digitised as a horizontal 3-D line based upon the mean elevation of the surface of the feature.

In addition to digitising drawings prepared using drawing film in the field, complex features, such as burials, are recorded using vertical photography, incorporating georeferencing points, which can then be blown up to 1:5 scale and digitised from the photographs by hand using a digitising tablet. The vector line drawings produced in this way can be printed at high resolution and at any scale. The data structure employed facilitates the preparation of publication drawings at any scale, driven by SQL queries managed within the Access database or from the Matrix Manager. More extensive vertical photographic mosaics covering some of the more complex areas have occasionally been created using the Quadropod, a lightweight portable vertical photography tower originally used on Philip Barker's excavations at Wroxeter. Even then the photo-mosaics have been created to enhance the understanding of areas that were drawn using conventional techniques, rather than to replace them.


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