Contents of .svx files: How do I?

Here is some example Survex data (a very small cave numbered 1623/163):

2 1 26.60 222  17.5
2 3 10.85 014   7
2 4  7.89 254 -11
4 5  2.98  - DOWN
5 6  9.29 271 -28.5

You can vary the data ordering. The default is:

from-station to-station tape compass clino

This data demonstrates a number of useful features of Survex:

Legs can be measured either way round, which allows the use of techniques like "leap-frogging", meaning that the legs alternate forwards and backwards.

Also notice that there is a spur in the survey (2 to 3). You do not need to specify this specially.

Survex places few restrictions on station naming, so you can number the stations as they were in the original survey notes. Although not apparent from this example, there is no requirement for each leg to connect to an existing station. Survex can accept data in any order, and will check for connectedness once all the data has been read in.

Each survey is also likely to have other information associated with it, such as instrument calibrations, etc. This has been omitted from this example to keep things simple.

Most caves will take more than just one survey trip to map. Commonly the numbering in each survey will begin at 1, so we need to be able to tell apart stations with the same number in different surveys.

To accomplish this, Survex has a very flexible system of hierarchical prefixes. All you need do is give each survey a unique name or number, and enter the data like so:

*begin 163
2 1 26.60 222  17.5
2 3 10.85 014   7
2 4  7.89 254 -11
4 5  2.98  - DOWN
5 6  9.29 271 -28.5
*end 163

Survex will name the stations by attaching the current prefix. In this case, the stations will be named 163.1, 163.2, etc.

We have a convention with the Austria data that the entrance survey station of a cave is named P<cave number>, so P163 in this case. We can accomplish this like so:

*begin 163
*equate 1 \P163
2 1 26.60 222  17.5
2 3 10.85 014   7
2 4  7.89 254 -11
4 5  2.98  - DOWN
5 6  9.29 271 -28.5
*end 163

The '\' means use the root prefix for the current file, so this equates the stations 163.1 and P163.

Specify the ordering and type of data

Ordering

The *DATA command is used to specify the ordering

Type

Stylename Data items required

Normal/SphPolar <FromStn> <ToStn> <Length> <Bearing> <Gradient>

Diving <FromStn> <ToStn> <Length> <Bearing> <FromDepth> <ToDepth>

[These styles are not yet implemented]

Cartesian <FromStn> <ToStn> <dx> <dy> <dz>

Topofil <FromStn> <ToStn> <FromCount> <ToCount> <Bearing> <Gradient>

CylPolar <FromStn> <ToStn> <VerticalLength> <PlanLength> <Bearing>

The units of each quantity may be set with the UNITS command.

Notes:

1. [This feature is not implemented, although the style is.] In DIVING data, either <FromDepth> or <ToDepth> may be replaced by an <OMIT> (default '-') if the respective survey station is mentioned in the previous line (assuming there is no change of depth gauge/water level). If the survey station does not appear in the previous line (or this is the first line of diving data), then an error is given.

2. [Not implemented, although the style is] Similarly, for TOPOFIL data <FromCount> may be replaced by an <OMIT> (default '-') if the reading is the same as the previous <ToCount>. If this is the first line of Topofil data, then an error is given. (It is best if both readings are input, rather than just the difference between them, to aid tracking down incorrect legs. If you do not agree, use NORMAL data style).

3. CARTESIAN data are relative to TRUE North not MAGNETIC North (i.e. they are unaffected by the calibration of DECLINATION). Also x is Easting, y is Northing, and z is height. This convention has been chosen because it gives right-handed axes, such that plotting x and y on a graph gives North up the page.

4 [Not implemented] CYLPOLAR (Cylindrical Polar) style data is included for completeness, since someone may have a use for it. Perhaps a Grade 3 survey, or when surveying with a level and stick (?). Let me know if you find a use so I can put a better justification for it in here!

Deal with Plumbs or Horizontals

PLUMBED LEGS should be given as 'UP' or 'DOWN'. They can be given as +90, or -90, but as they are not usually measured with the clino, but with a plumb of some sort, then it is useful to distinguish them in this way so that any clino adjustment is not applied to these values.

Note that a similar effect can be achieved by using the -N command line option to stop clino corrections being applied to -90 and +90 clino readings.

Up and Down are used like this, in place of the Clino reading. A dash (or a different specified 'OMIT' character) is given for the compass reading in the usual way

1 2 21.54 - UP
3 2 7.36 017 +17
3 4 1.62 091 +08
5 4 10.38 - DOWN

(U,D may be used instead of UP,DOWN (not case sensitive), or +V and -V).

Specify a BCRA grade

The *SD command can be used to specify the standard deviations of the various measurements (tape, compass, clino, etc). Examples files are supplied which define BCRA Grade 3 and BCRA Grade 5 using a number of *sd commands. You can use these by simply including them at the relevant point..

You can use them as follows:

*begin somewhere
; This survey is only grade 3
*include grade3
2 1 26.60 222  17.5
2 3 10.85 014   7
; etc
*end somewhere

The default values for the standard deviations are those for BCRA grade 5. Note that it is good practice to keep the *include Grade3 within *Begin and *End commands otherwise it will apply to following survey data, which may not be what you intended.

Specify different accuracy for a leg

For example, suppose the tape on the plumbed leg in this survey is suspected of being inaccurate for some reason, but that the other measurements and legs are believed to be okay:

*begin 163
*equate 1 \P163
2 1 26.60 222  17.5
2 3 10.85 014   7
2 4  7.89 254 -11
*begin
; the tape for this leg is somewhat suspect
*sd tape 0.5 metres
4 5  2.98  - DOWN
*end
5 6  9.29 271 -28.5
*end 163

Put in a radiolocation

This is done by using the *SD command to indicate that the 'leg' between two points in unusual. For a radiolocation you have an approximately vertical 'leg' between the underground station, and the surface station. The horizontal positioning of this is generally quite accurate, but the vertical positioning may be much less well known. You will need to represent the leg as a plumb, giving suitable SDs for the length and gradient. E.g: we have a radiolocation of about 50m depth +/- 20m and horizontal accuracy of say +/- 8m. Over 50m the +/-8m is equivalent to an angle of 9degrees, so that is the expected gradient error. 20m is the expected error in the length. To get the equivalent SD we assume that 95% of readings will be within 3 standard deviations of the error value. Thus we divide the expected errors by 3 to get the SD we should specify:

*SD length 6.67
*SD gradient 3 degrees.

For more information on the expected errors from radiolocations see Compass Points Issue 10.

Enter Diving Data

Diving Data is now accepted. You use the *Data command to specify that the following data is of this type.

Enter Theodolite data

Theodolite data is not yet explicitly catered for. You will need to convert it into equivalent compass and tape legs, or some other accepted format to process it. Note that if there is no vertical info in your theodolite data then you should use the SD commands to specify very low accuracy (High SD) in the vertical, but very high accuracy (low SD) in the horizontal and length info, so that the points will move in the vertical plane as required, but not in the horizontal, if the end points are fixed, or the survey is part of a loop.