Thursday, 2 April 2015
The science of getting lost
Being discombobulated I stopped. I could well have been going the right way but I didn't have a sense of my direction. This seldom happens to me and when it does I stop and reset to get reorientated. I had my compass out but it is little comfort knowing the compass directions derived from magnetic north when you don't know where you are. I knew I wanted to go SSE to intercept a jeep track that would take me in a southerly direction. SSE was the direction from the start of the track and not necessarily the direction required from where I stood. I am not quite sure what Casper made of my sudden halt. A walked around a bit and then told him we needed to get back to the gate to start again. We found a fence line and by following that in a northerly direction Casper found the gate. Starting back at the gate I gave my head a little shake to reset my internal gyro and tried again. We went in exactly the same direction but this time I had no doubts and we quickly picked up the track we were looking for. We bumped along this track for a short distance and then walked up a couple of steep sections all the while I was checking and double checking. Once we were at the top of a ridge that would lead us down to the fence line where we would have to stop and hop the fence Casper was ahead of me. It was a mistake. Not that Casper did anything wrong, it is just that I didn't have a proper sense of the distance we covered. I told him to look out for a fence line on our right hand side and mentioned that when it got close we were to cross to the fence line and hop over. He did just that.
Something wasn't right. The slope of the land did not correlate with my mental picture of what should have been in front of us. My light, although bright did very little to help. I told Casper I was going to go further down the track. He said he was happy to stay where he was and I climbed back over the fence and walked further down the jeep track. I walked for about 100 metres and saw the fence was a lot closer to the track as I had expected. Crossing to the fence I stepped on an old cycling shoe complete with cleat. I had seen this very shoe on my previous excursion and confident that this was exactly where I wanted to be. I picked the shoe up and hung it on the fence. After hopping over the fence I walked in Casper's direction to fetch him. Imagine my surprise when, as I walked down the straight fence line, I saw his headlight far off to my right. A short distance on I found a junction in the fence that I hadn't noticed before. Casper and I had crossed the wrong fence. It ran perpendicular to the fence we wanted. I reached him, retrieved my bike and we made our way back to the spot I had marked on the fence. I explained to Casper that all we had to do is head directly south and after a few hundred metres we would intercept the track that would take us on to Elandsberg farm. It's a no brainer. I did this same section at night in 2009 when riding with Glenn on the tandem and we made it look easy. The only difference this time round is that it was dark - there were no stars or skyline visible. The only way we could get a bearing was with a compass. That is where it got interesting. As most of us know, geographic north (true north) and magnetic north are not the same thing. Maps are oriented to true north which is a good thing as magnetic north has a nasty habit of wandering. It moves all the time. From Cradock magnetic north is way off to the west of true north. The trick is to know how much. On the last government ordinance maps of that area that I saw I seem to remember the magnetic declination (it's marked at the bottom of the maps) of the maps being something of the order of 18 degrees west. That means your compass will point 18 degrees further west than the true bearing if you are heading north. We were heading south which means the indicated bearing would deviate east 18 degrees, or so I though. The maps I last saw were dated late 70's early 80's and I thought 18 degrees a little steep so I aimed to walk just off South, 10 degrees or so. Today I googled the current magnetic declination for Cradock and found it to be a whopping 23 degrees west. That's massive. Certainly a whole heap more than I anticipated. The net effect is that we wandered off too far left. There is another interesting contributing factor that causes you to go off line. Every time you walk around a bush or try find a line through an obstacle,such as the dongas we were faced with, it is unlikely you will realign yourself on the same intended track once through. You will be some metres left or right of your previous bearing. Pick up your compass and continue on the same bearing and you will continue on a parallel line that will maintain your obstacle deviation. After a few hundred metres you could be 20, 30 or even 50 metres away from your target line. With the benefit of some light you will see the skyline. By aiming at a feature you do away with the parallel deviation and introduce converging paths. If the distance to the feature you head toward is fairly close the convergence effect is self correcting.
While this may all sound rather boring, to me it is fascinating. By understanding how we get it wrong we are able to apply the learning to avoid a reoccurrence.
When I spoke to Alex about it later he said he was surprised because we know the lay of the land and it is simple. True, except for a few things. Firstly, we had been on the go for nearly 40 hours with less than an hours sleep. While not aware of any ill effects I guess it might have played a part. The second challenge is selective visual attention. If you stand at the fence in daylight it is easy to see the track that you need to get to. Your brain, bombarded by many visual stimuli, is able to focus in on the target stimulus. In this case it correctly identifies the distant jeep track heading up the ridge as the way out. There is a high resolution of focus on this one object. Everything else is demoted to your periphery where it is scanned in low resolution and is stored in your brain with little detail. If the jeep track was not visible from the fence then it is probable that the stored memory would contain more detailed information.
As we drifted left I started seeing things that I was not familiar with. The dongas we encountered were huge. Nothing like the ones I remembered from previous years. Probably an effect of poor memory data and the effect of things looking bigger at night as you battle to get a sense of scale in a limit visual pool. Eventually I stopped and told Casper that it wasn't going well. To be continued....
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- Johannesburg, South Africa
- Just an ordinary guy who started riding in 2005 at the age of 45. I started with the ambition of completing the local 94.7 Cycle Challenge (94.7km). This is an annual road cycle race in and around Johanesburg. Some where along the way it become a race and not merely a completion excercise. I clocked a 2h54 in my first attempt only 6 months from my first trundle down the road and back. I was hooked and then discovered the magic of MTB. While my efforts on the road were credible, MTBing humbled me. Having said that, over the last 24 months I have competed in 9 multi-day events. I'm a very middle of the field rider, but I enjoy every minute of it.