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" (which is where 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 (see "Survey Station Names" in the previous section), 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 *export 1 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 CUCC Austria data that the entrance survey station of a cave is named P<cave number>, P163 in this case. We can accomplish this like so:
*equate P163 163.1 *entrance P163 *begin 163 *export 1 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 |
Say you have 2 underground surveys and 2 surface ones with 2 fixed reference points. You want to mark the surface surveys so that their length isn't included in length statistics, and so that Aven knows to display them differently. To do this you mark surface data with the "surface" flag - this is set with "*flags surface" like so:
; fixed reference points
*fix fix_a 12345 56789 1234
*fix fix_b 23456 67890 1111
; surface data (enclosed in *begin ... *end to stop the *flags command
; from "leaking" out)
*begin
*flags surface
*include surface1
*include surface2
*end
; underground data
*include cave1
*include cave2 |
You might also have a survey which starts on the surface and heads into a cave. This can be easily handled too - here's an example which goes in one entrance, through the cave, and out of another entrance:
*begin BtoC *title "161b to 161c" *date 1990.08.06 ; trip 1990-161c-3 in 1990 logbook *begin *flags surface 02 01 3.09 249 -08.5 02 03 4.13 252.5 -26 *end 04 03 6.00 020 +37 04 05 3.07 329 -31 06 05 2.67 203 -40.5 06 07 2.20 014 +04 07 08 2.98 032 +04 08 09 2.73 063.5 +21 09 10 12.35 059 +15 *begin *flags surface 11 10 4.20 221.5 -11.5 11 12 5.05 215 +03.5 11 13 6.14 205 +12.5 13 14 15.40 221 -14 *end *end BtoC |
Note that to avoid needless complication, Survex regards each leg as being either "surface" or "not surface" - if a leg spans the boundary you'll have to call it one or the other. It's good surveying practice to deliberately put a station at the surface/underground interface (typically the highest closed contour or drip line) so this generally isn't an onerous restriction.
The *DATA command is used to specify the data style, and the order in which the readings are given.
Plumbed legs should be given using 'UP' or 'DOWN' in place of the clino reading and a dash (or a different specified 'OMIT' character) in place of the compass reading. This distinguishes them from legs measured with a compass and clino. Here's an example:
1 2 21.54 - UP 3 2 7.36 017 +17 3 4 1.62 091 +08 5 4 10.38 - DOWN |
U/D or +V/-V may be used instead of UP/DOWN; the check is not case sensitive.
Legs surveyed across the surface of a static body of water where no clino reading is taken (since the surface of the water can be assumed to be flat) can be indicated by using LEVEL in place of a clino reading. This prevents the clino correction being applied. Here's an example:
1 2 11.37 190 -12 3 2 7.36 017 LEVEL 3 4 1.62 091 LEVEL |
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, 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.
For example, suppose the tape on the plumbed leg in this survey is suspected of being less accurate than the rest of the survey because the length was obtained by measuring the length of the rope used to rig the pitch. We can set a higher sd for this one measurement and use a *begin/*end block to make sure this setting only applies to the one leg:
2 1 26.60 222 17.5 2 3 10.85 014 7 2 4 7.89 254 -11 *begin ; tape measurement was taken from the rope length *sd tape 0.5 metres 4 5 34.50 - DOWN *end 5 6 9.29 271 -28.5 |
If your survey data contains multiple versions of each leg (for example, pockettopo produces such data), then provided these are adjacent to one another Survex 1.2.17 and later will automatically average these and treat them as a single leg.
This is done by using the *SD command to specify the appropriate errors for the radiolocation `survey leg' so that the loop closure algorithm knows how to distribute errors if it forms part of a loop.
The best approach for a radiolocation where the underground station is vertically below the surface station is to represent it as a plumbed leg, giving suitable SDs for the length and plumb angle. The horizontal positioning of this is generally quite accurate, but the vertical positioning may be much less well known. E.g: we have a radiolocation of about 50m depth +/- 20m and horizontal accuracy of +/- 8m. Over 50m the +/-8m is equivalent to an angle of 9 degrees, so that is the expected plumb error. 20m is the expected error in the length. To get the equivalent SD we assume that 99.74% 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:
*begin *sd length 6.67 metres *sd plumb 3 degrees surface underground 50 - down *end |
We wrap the radiolocation leg in a *begin/*end block to make sure that the special *sd settings only apply to this one leg.
For more information on the expected errors from radiolocations see Compass Points Issue 10, available online at http://www.chaos.org.uk/survex/cp/CP10/CPoint10.htm
Surveys made underwater using a diver's depth gauge can be processed - use the *Data command to specify that the following data is of this type.
Theodolite data with turned angles is not yet explicitly catered for, so for now you will need to convert it into equivalent legs in another style - normal or cylpolar are likely to be the best choices.
If there is no vertical info in your theodolite data then you should use the cylpolar style and use *sd command to specify very low accuracy (high SD) in the depth so that the points will move in the vertical plane as required if the end points are fixed or the survey is part of a loop.