Plotting With Polar Vs. Rectangular Coordinates

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Plotting With Polar Vs. Rectangular Coordinates

Postby GroundquestMSA » Jun 19, 2011 12:09 pm

I am attempting to learn surveying. Having limited formal education and no advanced mathematical skills, I am finding the idea of plotting with polar coordinates appealing. "On Station," however, deems such an approach unworthy for any but the smallest of caves. I have a few questions.

Is plotting with rectangular coordinates significantly more difficult than polar once the concept is well understood? Keep in mind that I am doing the plotting without the aid of any software.

Is there mapping software available that I could use from a slow dialup internet connection, or is purchasing a disk the best option?

How concerned should I be over survey error? I understand the need to be correct and I know that my personal satisfaction would greatly diminish if my map was extremely innacurate. However, in the smallish caves that I am surveying for mainly recreative purposes, should I panic over slight error if my map is still a clear, understandable representation of the cave?
After all, in caves that are not that complex, what real practical purpose does a map serve? Outside considerations of artistic excellence then, should I feel like I am wasting my time if a 1200' survey is off by a yard or two?
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Re: Plotting With Polar Vs. Rectangular Coordinates

Postby Bob Thrun » Jun 19, 2011 1:50 pm

GroundquestMSA wrote:Is plotting with rectangular coordinates significantly more difficult than polar once the concept is well understood? Keep in mind that I am doing the plotting without the aid of any software.

All cave surveying is done in polar coordinates (actually spherical). To convert to rectangular coordinates, you must apply trig functions to the measurements and keep cumulative sums of the rectangular coordinates. Then you must use gridded paper and count squares to find where to put each station dot. There is also the problem of closure adjustments.

To plot in polar coordinates you need either gridded paper and a protractor, or a drafting board with an adjustable protractor. With a drafting machine, which is a fancy adjustable protractor. I could plot faster than I could key in numbers. There is the problem of replotting to correct mistakes or change scale.
Is there mapping software available that I could use from a slow dialup internet connection, or is purchasing a disk the best option?

There are are several programs available. I use my own CMAP, but I have not written a good plotting back end. You have internet access. With a 56k modem you should be able to download even one of the larger programs in about an hour.
How concerned should I be over survey error? I understand the need to be correct and I know that my personal satisfaction would greatly diminish if my map was extremely innacurate. However, in the smallish caves that I am surveying for mainly recreative purposes, should I panic over slight error if my map is still a clear, understandable representation of the cave?
After all, in caves that are not that complex, what real practical purpose does a map serve? Outside considerations of artistic excellence then, should I feel like I am wasting my time if a 1200' survey is off by a yard or two?

I am very concerned with accuracy and closure adjustments, but I will admit that your distances would have to be off by 10 percent and your angles off by 10 degrees before anyone using the map as a roadmap would even notice. A resurvey would be needed to spot the errors.

Go caving with copies of someone else's maps to see what features you would like to have shown on the maps you make.
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Re: Plotting With Polar Vs. Rectangular Coordinates

Postby Spike » Jun 21, 2011 9:29 am

How small are we talking about and at what scale? Also did you take back sights, use a clinometer, or measure to the nearest tenth of a foot, or inch? If not go ahead and use the protractor and plot polar Coords. If you did take the time in the cave to record the above try downloading Walls (it's free but has a steeper learning curve and is ~5 MB) or you can easily make a spreadsheet to calculate Rectangular Coordinates using Excel or another similar program. Many folks now draft digitally, but I like seeing hand drawn maps too. Anyway have fun and good luck.
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Re: Plotting With Polar Vs. Rectangular Coordinates

Postby GroundquestMSA » Jun 21, 2011 2:12 pm

Spike wrote:How small are we talking about and at what scale?


I'm starting out on an approx. 400' and a 200'. I'm using compass tape and clinometer and measuring to the inch. I have taken backsights on occasion just to check myself but haven't been recording the data. What is the best scale ratio for this size cave when using ft. & inches?
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Re: Plotting With Polar Vs. Rectangular Coordinates

Postby Spike » Jun 21, 2011 3:30 pm

I would do 20 feet to the inch. Your 200' caves will fit on 8.5X11 and will still look ok scaled down for a guide book or such. The 400' map will fit on 11X17. Of course depending on how much the cave meanders you might fit the bigger ones on smaller common paper sizes.
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Re: Plotting With Polar Vs. Rectangular Coordinates

Postby hereiam » Aug 11, 2011 7:48 am

If you still have the need, you can also try a simple survey software Speleoliti that allows you to edit (copy,paste,correct,draw,print,export,...) both polar or rectangular form of data.
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