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Techniques : Drawing Frames

A drawing or planning frame can be used to record complex detail and associations in situations where there is too much to measure. The bulk of the drawing can be done by eye quickly and accurately without the need to measure. Details of the topography and seabed type can be recorded and a frame can be used vertically as well as horizontally for recording sections and areas of standing structure.

This is a very simple technique and very accurate over small areas. Where an area larger than one drawing frame needs to be recorded it is essential to set up survey control so all the separate drawings can be fitted together.

Construction

A typical drawing frame is 1m rigid square made from metal or plastic tubing subdivided into squares of 100 or 200mm using thin cord or elastic. Designs vary but the frame must be portable, must not distort and the strings must be tight. In use the frame should be horizontal so the frame may need adjustable legs and spirit levels on both sides.  Steel reinforcing mesh can also be used, this has the advantage of being tough and durable so can be left on site between dives.

The diver should be directly above each square as it is drawn. Double stringing the frame is an effective way to ensure that this happens, when both sets of strings are in line the diver knows he is in the correct position. Colour coding the strings helps to identify the grid square being drawn.

If a sheet of transparent acrylic or PVC is laid over a drawing frame, the detail can be drawn directly on to the sheet using a wax crayon or chinagraph pencil. Back on the surface you can use hand drawing, photography or scanning to scale down the drawn squares. Alternatively the squares can be traced off at the same scale onto drafting film. The original sheet can then be cleaned and reused.

Control

A complete site can be drawn up square by square or only a specific area covered, either way the position of each frame on the site must be found before it can be drawn up.  Frames can be moved along a baseline if a strip of frames is to be recorded, sometimes only positioning the ends of this baseline is sufficient to position the frames.

For larger areas the corners of each frame can be tied into the control network, however this can take a long time. A third method involves putting labelled markers over the site which are positioned relative to the control network, plastic survey markers are ideal for this. There must be enough markers for at least two to appear in each frame as it is drawn, so the markers must be shown on each drawn square along with its name.

Ensuring coverage of an area usually means that some overlap is required between frame squares. Some overlap can be useful in aligning adjacent squares when drawing up the survey however this should not be the only method for positioning squares when drawing up. Before moving a frame, markers can be placed to indicate the corners of the area just drawn so the next frame can be aligned accordingly.

Method

  1. Set the frame over the area to be recorded.
  2. Position yourself over the frame and use the squares as a reference
  3. Ensure that you are vertical above each square as it is drawn.
  4. Draw what you see directly onto a form with a grid marked on it at a smaller scale.
  5. Or draw at 1:1 scale on to a clear plastic sheet laid over the drawing frame.
The frame must be placed close to the subject so detail can be seen. In poor visibility the operation will be slower but should not be any less accurate.  A set of symbols and conventions can be developed for each project so various materials and features are represented in the same way on each drawn square.

Drawing up

Recording using drawing frames produces lots of small squares to join up to form a site plan. The original drawings should not be inked over or stuck on to the main site plan, the originals are the primary record and should be kept as a check on the final plan.

Each original drawn square should have additional information marked on it:
  • Site code
  • Date drawn
  • Name of diver
  • Magnetic north direction
  • Visibility
  • Individual or dive reference number
  • Location description

To draw up the plan by hand, a site plan of the same scale as the squares is required showing the position of the control markers. Each square can then be aligned on its appropriate marker and drawn on to the plan.

To do this using a computer involves producing a computer-generated plan of the site. The plan should show the position of the control markers. The original drawings can then be scanned and overlaid onto the site plan digitally.

Although it is possible to fit the squares together just by lining up features on the edges this is not recommended. It is important that control points are included in the plan otherwise the overall shape of the site tends to distort. In addition, with no control included in the plan you have no idea of the accuracy of that plan.

 

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