Cave Surveying Group Field Meeting, May 1996

The Cave Surveying Group (in conjunction with the Cave Radio & Elecronics Group) held a field meet in the Peak District on the weekend 18th-19th May 1996.


Wookey reports:

The meet was well-attended overall, although most of those present were 'Cave Radio' people rather than 'Surveyors'. The Friday night was exceptionally cold, getting down to just about freezing. I arrived at about 1am and couldn't be bothered putting up a tent, but I had forgotten my karrimat so I had an extremely chilly night in my van - joy! This promted a very early rise at about 7.30am.

Full cooked brekky was provided and duly eaten. The Cave radio mob collected all their bizzare gear together and set off to Stoney Middleton and Carlswalk cavern.

Team surveyor, which at this point consisted of Wookey and Andy Atkinson unloaded a small pile of computers, instruments and surveys and got down to business.

The areas of discussion for the first day were:

Final survey production on computer
We have generated an interest in this as our (Cambridge University Caving Club) cave in Austria has got bigger and bigger, and the practicalities of producing a new plan & elevation of 15km of cave in a year have got out of hand. The drawing itself takes ages, but the sticking on of labels, drawing of grid, adding of cross-sections etc is just as time-consuming, and would be much easier on some kind of CAD/drawing system, if only because at least things would be horizontal when they should be.

Actually drawing on the computer is difficult though, so we are currently looking at creating film originals of each section of cave, then importing them into the computer to be stuck together, labelled & annotated before printing.

The pictures can either be scanned or traced on a graphics tablet. We only have access to a scanner so we opted to test out the limitation of this process first. A sizeable section of Kaninchenhöhle, comprising about 15 surveys had previously been drawn onto paper (as extended elevations), then traced onto final film version. A 5cm N-S/E-W cross included for orientation and scaling of the final sketch, and X's used to mark the stations at the 'joins' of different sections. These had been scanned in before the weekend.

We used a couple of different vectorising packages to turn the large bitmaps into vector images again. This worked OK, but many of the lines became broken, and all small detail (eg traverse 'T's and the crosses we put on for lining up the plots) was poorly reproduced. [I have since found that scanning at higher resolution to give about 8pixels across a typical line width will give massively improved results] We found that the effects were much the same with both Adobe Streamline and CorelTrace, suggesting that it was an algorithmic problem rather than one of poorly written software.

It would be intersting to see how much better the results are with a graphics tablet and 'manual' vectorising. Anyone got one we can borrow?

Having got the pics into the computer there were a number of other issues to consider. We wanted to be able to manipulate each 'cave section' independently of the others, so that sections can be moved around to line them up. This is easy to start with, but as soon at the section is ungrouped, in order to change any lines within it, then it becomes impossible to regroup if there are any overlying cave sections (which there inevitably are). This problem could be got around by putting different cave sections on different layers.

The other thing that we need is to be able to select which elements will be printed. This is primarily a scale issue. For a small plot then some of the detail is not needed as it will be illegible and clutter up the plot. Also the size of labels needs to change for printing at different scales. As the plot gets smaller then the labels need to be larger otherwise they become illegible. These requirements are also best met by the labels, walls and details being on separate layers so that we can choose which to print.

Unfortunately normal 2D drawing packages do not really allow the above. If you put parts of an object on different layers, then the act of grouping things on those multiple layers moves them all to the same layer. It is necessary to group the different aspects of a cave section (walls, detail, labels) so that when it is moved they all move together.

This led us to determine that only CAD systems could really do what we wanted, although a workaround for the drawing packages would be to do all the fine editing of cave sections in a separate file in multiple sections, and then only assemble them for a final plot. We will be trying out this techique and reporting back on how it works.

Whilst working out what was required we tried to specify a set of layers for all the possible uses we could think of for the survey. ie this is looking at layers for use a way of selectively including things to appear on the final plot. This is the list we produced.

Layer Definition for CUCC surveys

Wookey & Andy Atkinson 1996.05.18
Things we need:
                                                        Layer number
Walls -     Solid walls (thick 0.35)                           1
            Guessed walls (dashed)                             1
            Wall corners - extendeds only (thin)               1
            Undercuts                                          1
            Underneath lines                                   1
            Truncation lines                                   1
            Extracted cave position ( eg entrance, GP)         1
            

Survey -  Centerline                                           2
          Stations                                             3
          Hydrological connections                             8

Passage detail
      Blocks - thin lines                                      4
      traverse T's                                             4
      static water                                             9
      flowing water                                            9
      sumps                                                    9
      sand                                                     9
      mud                                                      9
      stones                                                   9
      rocks                                                    9
      boulders                                                 9
      drops/climbs/shelves                                     5
      avens/roof height change                                 6
      slopes                                                   5
      ice                                                      9
      snow                                                     9
      formations                                               9
      gours                                                    9
      flowstone                                                9
      rigging                                                  7
      scallops                                                10
      ripplemarks                                             10
      
Labelling
      Area names                                              20
      Names                                                   21
      pitch/climb labels                                      22
      grade markings                                          22
      desciptives (ie too tight)                              22
      QMs                                                     23
      comments                                                24
      faults                                                  25
      draughts                                                25
      cross section ids                                       26
      0-distances (extendeds)                                  1
      
Other
      Grid                                                    31
      North arrow                                             30
      Scale                                                   30
      Name and details                                        30
      location                                                30

Recent Survey software releases were installed and examined, primarily as light relief from all the hard thinking required for the other items on the list. These were

On the second day

we looked at To be continued in the next issue of Compass Points, if not before...

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