Cave Surveying
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Publication: An introduction to Cave Surveying
A new edition of this booklet in the Cave Studies series was published in July 2002. The booklet
include information on prices of instruments, surveying software, useful web sites and so on.
For more information about cave surveying visit BCRA Cave
Surveying Group
Information about radio-location can be found by visiting BCRA
Cave Radio & Electronics Group and using their search
engine.
Two archived articles from the old CSG web site that might still be of interest are
Cave Surveying Notes (1993) and
Cave Survey Software - An Overview (2001)
BCRA Survey Grades
As revised for inclusion in
Cave Surveying, July
2002
Table 1: BCRA gradings for a cave line survey
- Grade 1
- Sketch of low accuracy where no measurements have been made
- Grade 2 (use only if necessary, see note 7)
- May be used, if necessary, to describe a sketch that is intermediate in accuracy between
Grade 1 & 3
- Grade 3
- A rough magnetic survey. Horizontal & vertical angles measured to ±2.5º;
distances measured to ±50 cm; station position error less than 50cm.
- Grade 4 (use only if necessary, see note 7)
- May be used, if necessary, to describe a survey that fails to attain all the
requirements of Grade 5 but is more accurate than a Grade 3 survey.
- Grade 5
- A Magnetic survey. Horizontal and vertical angles measured to ±1º; distances
should be observed and recorded to the nearest centimetre and station positions identified to less
than 10cm.
- Grade 6
- A magnetic survey that is more accurate than grade 5, (see note 5).
- Grade X
- A survey that is based primarily on the use of a theodolite or total station instead of
a compass, (see notes 6 and 10 below).
Notes
- The above table is a summary and is intended only as an aide memoire; the
definitions of the survey grades given above must be read in conjunction with these notes.
- In all cases it is necessary to follow the spirit of the definition and not just the
letter.
- To attain Grade 3 it is necessary to use a clinometer in passages having appreciable
slope.
- To attain Grade 5 it is essential for instruments to be properly calibrated, and all
measurements must be taken from a point within a 10cm diameter sphere centred on the survey
station.
- A Grade 6 survey requires the compass to be used at the limit of possible accuracy, i.e.
accurate to ±0.5º; clinometer readings must be to the same accuracy. Station position
error must be less than ±2.5 cm, which will require the use of tripods at all stations or
other fixed station markers ('roofhooks').
- A Grade X survey must include on the drawing notes descriptions of the instruments and
techniques used, together with an estimate of the probable accuracy of the survey compared with
Grade 3, 5 or 6 surveys.
- Grades 2 and 4 are for use only when, at some stage of the survey, physical conditions
have prevented the survey from attaining all the requirements for the next higher grade and it is
not practical to re-survey.
- Caving organisations etc, are encouraged to reproduce Table 1 and Table 2 in their own
publications; permission is not required from BCRA to do so, but the tables must not be
reprinted without these notes.
- Grade X is only potentially more accurate than Grade 6. It should never be
forgotten that the theodolite/Total Station is a complex precision instrument that requires
considerable training and regular practice if serious errors are not to be made through its use!
- In drawing up, the survey co-ordinates must be calculated and not hand-drawn with
scale rule and protractor to obtain Grade 5.
Table 2. BCRA gradings for recording cave passage detail
- Class A
- All passage details based on memory.
- Class B
- Passage details estimated and recorded in the cave.
- Class C
- Measurements of detail made at survey stations only.
- Class D
- Measurements of detail made at survey stations and wherever else needed to show
significant changes in passage dimensions.
Notes
- The accuracy of the detail should be similar to the accuracy of the line.
- Normally only one of the following combinations of survey grades hould be used:
1A,
3B or 3C,
5C or 5D,
6D,
XA, XB, XC or XD.
