| An introduction to Cave
Surveying - New Edition
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. From time to time, updates to that information will be available as a
free insert, and will also be published on this web page.
For more information about cave surveying visit the home
page of BCRA's Cave Surveying Group
| BCRA Survey Grades
As revised for inclusion in the new edition of Cave
Surveying, July 2002
Table 1: BCRA gradings for a cave line survey
- Grade 1
- Sketch of low accuracy where no measurements have been
- Grade 2 (use only if necessary, see note
- 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
- 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
- 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
- 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).
- 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.
- 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:
3B or 3C,
5C or 5D,
XC or XD.
British Cave Research Association (UK
registered charity 267828). Registered Office: The Old Methodist Chapel, Great
Hucklow, BUXTON, SK17 8RG
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