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Re: Caves in Maryland

" It turns out that there actually is one in Montgomery County, Maryland. It's called Devil's Den Cave in Paint Branch on the Federal Research Center property in the White Oak area of Silver Spring. It's about 60 feet in length. I used to work there before it was the Federal Research Center. I...
by Bob Thrun
Dec 24, 2013 9:13 pm
 
Forum: Caving General Discussion and Questions Forum
Topic: Caves in Maryland
Replies: 13
Views: 11498

Re: BBC: Sumatra coastal cave records stunning tsunami histo

The story says each tsunami deposited a layer of sediments on top of a layer of guano. The guano was deposited by bats between tsunamis. Wouldn't the tsunami also wash away some of the previous deposits?
by Bob Thrun
Dec 12, 2013 9:14 pm
 
Forum: Caves, Caving In The News Forum
Topic: BBC: Sumatra coastal cave records stunning tsunami history
Replies: 3
Views: 5966

Re: Camp Goblin device that is interesting

The teeth on the ASAP look scary. Whether they will damage the rope depends on the rope construction, rope size, and cam angle. You would have to make a test to know for sure. Heightec claims its X-Cam design will damage the rope less than other designs. The Lyon report, http://www.hse.gov.uk/resear...
by Bob Thrun
Dec 1, 2013 5:53 pm
 
Forum: On Rope!
Topic: Camp Goblin device that is interesting
Replies: 10
Views: 18477

Re: Camp Goblin device that is interesting

It is simlar to the Petzl ASAP, if anyone has knowledge of that instrument The Goblin and ASAP are only similar in that they are both fall arrest devices. The ASAP is unique among fall arrest devices because it uses an inertia reel similar to what is found an many seatbelts. The inertia reel is the...
by Bob Thrun
Dec 1, 2013 4:16 am
 
Forum: On Rope!
Topic: Camp Goblin device that is interesting
Replies: 10
Views: 18477

Re: Laser Targets: Important?

[ Maybe there's a shortcut I'm not aware of ... are you saying that when you leave a space between numbers that all the various software programs recognize this as feet and inches? All this time I've been converting inches and fractions of inches into decimals before entering the data. It's one of ...
by Bob Thrun
Nov 7, 2013 2:22 pm
 
Forum: Survey and Cartography Forum
Topic: Laser Targets: Important?
Replies: 25
Views: 30920

Re: Laser Targets: Important?

[ If you go to an engineering scale, even if you stay with feet, i.e. feet, tenths of feet, hundredths of feet, you will find it much easier to enter the data into a computer, I am puzzled by the claim that feet and decimals are easier to enter into a computer than feet and inches. I have heard thi...
by Bob Thrun
Nov 6, 2013 12:31 pm
 
Forum: Survey and Cartography Forum
Topic: Laser Targets: Important?
Replies: 25
Views: 30920

Re: Two Points of Contact Rule

Various reference sources mandate that with respect to ascenders and other rope grabs, two gripping points of contact contacted at or above the user's waist must be maintained at all times during changeovers, and while crossing obstacles such as knots and rebelays. How about three points of contact...
by Bob Thrun
Nov 6, 2013 11:53 am
 
Forum: On Rope!
Topic: Two Points of Contact Rule
Replies: 44
Views: 54471

Re: Testing a Digital Compass

The very first digital compass on the market was intended for boaters. I have one that I bought from another caver after he tried it. It has rudimentary sights and a single magnetic sensor. It reads the direction of the magnetic field in the plane of the sensor. It does not measure the direction of ...
by Bob Thrun
Nov 4, 2013 7:40 pm
 
Forum: Survey and Cartography Forum
Topic: Testing a Digital Compass
Replies: 13
Views: 17675

Re: Laser Targets: Important?

We've been cutting out circles from the bottom of white plastic quart yogurt containers and bringing them in with the survey equipment. Durable, cheap, waterproof, washable, and the most reliable Better yet, put some retroreflective tape (like Scotchlite) on your target. You can get it at any auto ...
by Bob Thrun
Oct 31, 2013 7:46 pm
 
Forum: Survey and Cartography Forum
Topic: Laser Targets: Important?
Replies: 25
Views: 30920

Re: compass file help

Compass uses plain text files for its input. You do not have to use the Cave Editor. Any text editor is capable of splitting the .Dat file. The only thing you have to be careful about is that each survey ends with a formfeed character. With a decent editor, you should see the formfeeds. Edit: Notepa...
by Bob Thrun
Oct 20, 2013 10:11 am
 
Forum: Survey and Cartography Forum
Topic: compass file help
Replies: 8
Views: 10043

Re: Cleaning Rope

I have been told that a pressure washer can damage rope by forcing contaminants into and/or through the sheath. I have not seen any testing to verify this. Petzl warns against using them in their instructions for use (see below). Anyone have emperical info on this topic? This is Bruce Smith's Myth ...
by Bob Thrun
Oct 8, 2013 4:03 pm
 
Forum: On Rope!
Topic: Cleaning Rope
Replies: 29
Views: 38398

Re: True and N compass

The NOAA site uses the IGRF magnetic models that cover the whole earth. It smooths through some local variaations. You should verify its numbers by a surface survey. I have found the IGRF numbers accurate for my caving area. A declination map from an older book, say pre-1950, shows a lot more wiggle...
by Bob Thrun
Sep 14, 2013 2:47 pm
 
Forum: Survey and Cartography Forum
Topic: True and N compass
Replies: 6
Views: 8011

Re: Interior walls?

The use of heavy lines to delinate interior walls or bedrock pillars is a good idea. However, the exterior walls should be just as heavy. The walls should be the heaviest lines on the map.
by Bob Thrun
Jul 24, 2013 2:50 am
 
Forum: Survey and Cartography Forum
Topic: Interior walls?
Replies: 16
Views: 20641

Re: How do we define the footprint of a cave?

I propose that the footprint should be defined as the smallest convex polygon that encloses the horizontal extent of the cave. This is the Convex Hull Problem. I have two books on Computational Geometry. They each devote a whole chapter to the Convex Hull, showing different ways to solve the proble...
by Bob Thrun
Jun 13, 2013 12:36 pm
 
Forum: Survey and Cartography Forum
Topic: How do we define the footprint of a cave?
Replies: 13
Views: 16163

Re: How to document historical graffiti?

Graffiti from the years you mention would be scratched into the rock. I photographed some old signatures. There was no one good lighting angle. Some of the scratched strokes would show shadow patterns while others would be evenly illuminated and therefore invisible in the picture. I set up my camera...
by Bob Thrun
May 1, 2013 6:17 am
 
Forum: Conservation Forum
Topic: How to document historical graffiti?
Replies: 20
Views: 54152
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