Techniques: Planning or Drawing Frames
Version date: 16 October 2016
Fig 1: Planning frame used for recording timber underwater
A drawing or planning frame is used to record complex detail and associations in situations where there is too much to measure directly. The frame is placed over the area to be recorded and the features in the area are drawn to scale on a pre-printed form. An entire site can be drawn up square by square with a planning frame or only a specific area recorded in detail.
The bulk of the drawing can be done by eye quickly and accurately without the need to make direct measurements. 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 correctly.
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 yet rugged, must not distort too much when laid on the ground and the guide strings must be tight.
Steel reinforcing mesh can also be used, this has the advantage of being tough and durable so can be left on the site when not in use.
The person doing the recording has to be directly above each square as it is being drawn. When first learning the technique having two sets of strings on the frame one above the other is an effective way to ensure that this happens, when both sets of strings are in line then the view is directly above the square being recorded.
In use the frame should be approximately horizontal. Some more complicated frames have adjustable legs that can be set to different heights but these can be difficult to move around underwater. If there is plenty of time available on site then a better result will be obtained by levelling the planning frames using a bubble level, but often time is limited on site so simply estimating the level by eye is sufficient.
In really poor visibility it can be difficult to get far enough away from the frame to be positioned directly above it yet still be close enough to see the features to be recorded. In these conditions a sheet of clear plastic can be used instead, laid over the frame the features can be drawn directly on to the plastic using a chinagraph pencil. In poor visibility a yellow pencil works better than a black one (Fig. 5). When the drawing has been completed the plastic sheet can be photographed or hand drawn to scale on a planning frame form. Once copied the plastic sheet can be cleaned and reused. See the research page: The Accuracy of Planning Frame Drawings.
Fig 2: Planning frame made from square plastic tubing
Fig 3: Stainless steel planning frame
The position and orientation of each drawn frame must be determined before the drawing can be added to the site plan. Two methods are usually used to position a planning frame on a site; using Detail points to position two corners of the frame or using a baseline between two survey control points. Two points need to be used so that both the position and orientation of the frame are recorded (Fig. 4).
Both positioning methods require that a 3D survey control network has been set up on the site. For really small sites it is possible to record both sides along a single baseline but this limits the recorded strip to being 2m wide. For any job bigger than this a survey control network is required as planning frames record in great detail and need the very accurate positioning that this method provides, see the page about 3D Trilateration.
Two corners of a planning frame can be positioned using trilateration in the same way that any other Detail points are positioned, using four distance measurements to nearby survey control points plus a depth or height measurement.
Fig 4: Different methods that can be used for positioning planning frames
With a tape measure baseline laid between two control points the planning frame can be placed anywhere along the tape and its position can easily be calculated; this method is the most efficient for recording large areas of a site. The frame is placed adjacent to the baseline at one end and that square recorded, the frame can then be moved along the baseline 1m and the procedure repeated, or the frame can be moved to the other side of the baseline to record that. Eventually both sides of the baseline can be recorded along its whole length as a 2m wide strip.
Using a Planning Frame
The area of seabed under the frame is drawn to scale on a pre-printed form, usually at a scale of 1:10 or 1:20. It is usually convenient to tape the form to a drawing board to keep it in place, quick recorders may need to tape forms on both sides of the board.
- Set the frame carefully over the area to be recorded, ensure the frame does not accidentally damage what you are recording
- Make sure the frame is as level as possible
- Position yourself over the frame, using the squares as a reference identify which square on the frame corresponds to which square on the form
- Ensure that you are directly above each square as it is drawn
- For each square, start by marking on the form where the edge of each feature crosses the boundary of the square. This will result in a number of tick marks around the outside of each square
- Next join the lines that cut across the square
- Using the drawn lines as a guide add the extra lines and detail to the square
When working in a team the recording will be done by different people so it is important to make sure that everyone records in the same way:
- The smallest size of feature to record has to be decided at the start of a project, this is known as the level of detail. At a scale of 1:10 objects 20mm or bigger can usually be drawn. Note that each frame will take longer to draw if a smaller level of detail is chosen.
- 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
As well as providing space for the scaled frame drawing the form should include the name of the site, the site code, the name of the person doing the recording and the name of the drawing frame. If a baseline is used for positioning the name of the baseline used for positioning and how far along the baseline the frame was placed should be added. If detail points are used for positioning then their names should be clearly marked on the appropriate corners of the frame drawing. Links to example forms are below:
It is possible to record a planning frame on ordinary squared paper however in practice it takes time to work out which square is which while recording so pre-printed forms have been found to be more efficient.
Fig 5: 1m square plastic sheet used instead of a frame
Recording each square metre of a site will produce many small scale drawings which need to be fitted together to make a plan.
Fitting the squares together can be done by hand. It is better to copy the original drawings and use the copies to make the plan as the originals are part of the primary record and should be kept so they can be checked against the final plan. Although it is possible to fit the squares together just by lining up the edges this is not recommended as mistakes in alignment grow bigger as each square is added. It is important that control points are included in the plan otherwise the overall shape of the site tends to distort, a similar problem happens when making a photomosaic. See the page about Photomosaics.
Creating a plan by hand is time consuming and errors in positioning may add unwanted errors in the plan. A better method is to use Site Recorder as this has tools to import, digitise and automatically position planning frame drawings on the main site plan. Each frame drawing is scanned or photographed and imported in to a Drawing Frame object in the program. The scanned drawing is then scaled to fit the frame, the points or baseline used to position the frame are selected then the drawing can be seen in position on the site plan. The drawing can then be digitised using individual Layers to separate materials of different types. Previously recorded squares can also be shown alongside the latest one so features that appear in more than one square can be joined correctly. lastly, the scanned drawing can be hidden leaving just the digitised outline adding new details to the site plan.
An example of planning frames used in Site Recorder can be seen in the recording of the Royal Navy fireship Firebrand (1707), see the Firebrand page.
- Drawing slate - An A4 or A5 size PVC slate, pencil and waterproof paper for making notes
- Planning frame - A planning frame can be used to help correct distortions in the photographs