Spooky Navigation Accuracy

I noticed that Message-ID: <[email hidden]> from Paul
Cummings contained the following:

Quoted message said:

Eventually, we saw some houses, so I assumed I had gone slightly too far
east. Still, to complete the test, I would carry on on my bearing. I saw
one house and a white patch on the left hand side. This was on the bearing,
so we aimed for the white patch. The white patch became a van. Sitting
behind the van was my car. The van had not been there when we parked, so I
could not have known, but we had walked 1.5km on a bearing of 145 degrees
and finished within a metre of where we wanted.

I suppose that for every leg in the journey the error can either take
you closer to the true bearing or further away. Over a large number the
differences should cancel out.

Assuming a leg length of 30 metres and an accuracy of plus or minus 3
degrees then the maximum distance offline equals plus or minus tan3*30

Using this assumption, I've just written a script which generates random
errors within a range and then adds them all together to give a final
accuracy reading.

You can check it out here
www.ckdog.co.uk/test/bearing_error.php

You can change the data and try different distances/accuracies

The results are so surprising (to me at any rate) that I'm posting the
basic code below in case I've made a mistake.

<?php
//set up parameters
$dist=1500;
$leg=10;
$accuracy=3;
$var=0;
//run script 'number of legs' times
for($i=0;$i<($dist/$leg);$i++){
//generate a random error
$error=rand(-$accuracy,$accuracy);
//calculate distance 'off line' and add to $var
$var= $var+round((tan(deg2rad($error))*$leg),2);
}
//print distance 'off line'
echo "$var<br>";

?>

The whole code for the page with the form is here
http://www.ckdog.co.uk/test/bearing_error.phps

--
Geoff Berrow (put thecat out to email)
It's only Usenet, no one dies.
My opinions, not the committee's, mine.
Simple RFDs http://www.ckdog.co.uk/rfdmaker/

Paul Cummings <[email hidden]> wrote

Quoted message said:

I was out walking the Surrey Hills yesterday (around Holmbury and Pitch
Hills if you want to know). For those that don't know, this area is
relatively hilly (for south east England) and largely wooded with a mixture
of Beech, Oak, Chestnut, Scots Pine etc etc. There is quite a lot of
bracken, fern and gorse cover on the floor.

We were about 1.5km from the car and decided to walk on a bearing back to
the car. I worked out exactly where we were. A quick look at the map and I
figured we needed to walk on about 145 degrees back to the car. As this was
a test of my navigation accuracy, we decided not to aim off, but aim dead on
the car.

I took my first bearing and found a tree about 30m away on the line. We
walked to it. From there, I took my next bearing and so on. Each leg was
never more than about 30m and often down to about 10m. Sometimes the scrub
got up to about chest height. We also had a problem with a large
Rhododendron bush that blocked our path and lead to some careful navigation
around it.

Eventually, we saw some houses, so I assumed I had gone slightly too far
east. Still, to complete the test, I would carry on on my bearing. I saw
one house and a white patch on the left hand side. This was on the bearing,
so we aimed for the white patch. The white patch became a van. Sitting
behind the van was my car. The van had not been there when we parked, so I
could not have known, but we had walked 1.5km on a bearing of 145 degrees
and finished within a metre of where we wanted.

My friend bowed down humbly and described it as navigation using the force.
I called it pure luck, but I was very surprised at being able to walk so
accurately.

If anyone thinks this was easy, let me assure you I would rather navigate
across the Brecons or Snowdonia any time than through Surrey woods. The
woods often have paths not on the map and map paths that do not exist on the
ground.

Amazing how a series of navigation errors can combine to get you to
exackly where you want to be. :-) :-)
--
Gordon

Paul Cummings said:

I was out walking the Surrey Hills yesterday (around Holmbury and Pitch
Hills if you want to know).

Oh spooky!

I was doing a loop from Gomshall across to Shere down Ponds Lane
through Hurt Wood and past the Volunteer at Sutton Abinger - lack of
time to get from there to Gomshall Station precluded sampling the ale
:-(

Do you have a GPS track log by any chance? Looking at mine I see we
were in Hurt Wood from about 14:00 and passed Gasson Farm at 14:30.

Quoted message said:

If anyone thinks this was easy, let me assure you I would rather navigate
across the Brecons or Snowdonia any time than through Surrey woods. The
woods often have paths not on the map and map paths that do not exist on the
ground.

Amen. And the GPS was not a lot of help yesterday thanks to the wet
leaves.
--
Phil Cook looking north over the park to the "Westminster Gasworks"

On Sun, 7 Nov 2004 08:08:34 -0000, "Paul Cummings"
<[email hidden]> wrote:

| I was out walking the Surrey Hills yesterday (around Holmbury and Pitch
| Hills if you want to know). For those that don't know, this area is
| relatively hilly (for south east England) and largely wooded with a mixture
| of Beech, Oak, Chestnut, Scots Pine etc etc. There is quite a lot of
| bracken, fern and gorse cover on the floor.
|
| We were about 1.5km from the car and decided to walk on a bearing back to
| the car. I worked out exactly where we were. A quick look at the map and I
| figured we needed to walk on about 145 degrees back to the car. As this was
| a test of my navigation accuracy, we decided not to aim off, but aim dead on
| the car.
|
| I took my first bearing and found a tree about 30m away on the line. We
| walked to it. From there, I took my next bearing and so on. Each leg was
| never more than about 30m and often down to about 10m. Sometimes the scrub
| got up to about chest height. We also had a problem with a large
| Rhododendron bush that blocked our path and lead to some careful navigation
| around it.
|
| Eventually, we saw some houses, so I assumed I had gone slightly too far
| east. Still, to complete the test, I would carry on on my bearing. I saw
| one house and a white patch on the left hand side. This was on the bearing,
| so we aimed for the white patch. The white patch became a van. Sitting
| behind the van was my car. The van had not been there when we parked, so I
| could not have known, but we had walked 1.5km on a bearing of 145 degrees
| and finished within a metre of where we wanted.
|
| My friend bowed down humbly and described it as navigation using the force.
| I called it pure luck, but I was very surprised at being able to walk so
| accurately.
|
| If anyone thinks this was easy, let me assure you I would rather navigate
| across the Brecons or Snowdonia any time than through Surrey woods. The
| woods often have paths not on the map and map paths that do not exist on the
| ground.
|
| Anyway, that's all for now, time for breakfast.

Not spooky at all. When we look at a map we see everything on it between
where we are and where we want to be. We note and use wood boundaries,
contours everything on the map, not to mention memory of what you saw on
the trip out and other trips in the area. So I suggest that you thought
you were only using only the bearing, but subconsciously corrected your
course, using contours, memory etc. etc. When we were Hunter Gatherers,
we did not have paper maps, but we found our way round quite well.

--
Dave F

"Paul Cummings" wrote

Quoted message said:

If anyone thinks this was easy, let me assure you I would rather navigate
across the Brecons or Snowdonia any time than through Surrey woods. The
woods often have paths not on the map and map paths that do not exist on
the
ground.

Yes, and in autumn all the path disappear under leaves anyway.

--
Regards
Bob
In Runnymede, 17 miles West of London

Geoff Berrow <[email hidden]> wrote

Quoted message said:

I noticed that Message-ID: <[email hidden]> from Paul
Cummings contained the following:

Quoted message said:

Eventually, we saw some houses, so I assumed I had gone slightly too far
east. Still, to complete the test, I would carry on on my bearing. I saw
one house and a white patch on the left hand side. This was on the bearing,
so we aimed for the white patch. The white patch became a van. Sitting
behind the van was my car. The van had not been there when we parked, so I
could not have known, but we had walked 1.5km on a bearing of 145 degrees
and finished within a metre of where we wanted.

The results are so surprising (to me at any rate) that I'm posting the
basic code below in case I've made a mistake.

<?php
//set up parameters
$dist=1500;
$leg=10;
$accuracy=3;
$var=0;
//run script 'number of legs' times
for($i=0;$i<($dist/$leg);$i++){
//generate a random error
$error=rand(-$accuracy,$accuracy);
//calculate distance 'off line' and add to $var
$var= $var+round((tan(deg2rad($error))*$leg),2);
}
//print distance 'off line'
echo "$var<br>";

?>

The whole code for the page with the form is here
http://www.ckdog.co.uk/test/bearing_error.phps

Why were they surprising? I worked it out in about 10 seconds with a
bit of common sense. See my other post.

If you drop a piece of buttered toast on the floor many times, on
average it will land on its edge.

It never does of course...... :-)
--
Gordon

Phil Cook <[email hidden]> wrote

Quoted message said:

Amen. And the GPS was not a lot of help yesterday thanks to the wet
leaves.

Why? Was the sand bunker on the loco empty?
--
Gordon

Gordon said:

Phil Cook <[email hidden]> wrote

Quoted message said:

Amen. And the GPS was not a lot of help yesterday thanks to the wet
leaves.

Why? Was the sand bunker on the loco empty?

Loco? What's one of those? 99.99% of passenger trains in the
south-east are MUs of one sort or another.

There was plenty of sand on my walk but mostly in the wrong places.
Traction was only lacking on the muddy sections of Ponds Lane and that
was mostly leaf free. The wet leaves causing the GPS problems were
still on the trees.
--
Phil Cook looking north over the park to the "Westminster Gasworks"

"Phil Cook" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Paul Cummings said:

I was out walking the Surrey Hills yesterday (around Holmbury and Pitch
Hills if you want to know).

Oh spooky!

I was doing a loop from Gomshall across to Shere down Ponds Lane
through Hurt Wood and past the Volunteer at Sutton Abinger - lack of
time to get from there to Gomshall Station precluded sampling the ale
:-(

I am finding it more and more difficult to find routes in the 15-25km range
within this area (inc Leith Hill, Box Hill etc) which mostly avoid roads
and built up areas, so if you have any, I would be very grateful.

Quoted message said:

Do you have a GPS track log by any chance? Looking at mine I see we
were in Hurt Wood from about 14:00 and passed Gasson Farm at 14:30.

Until I get around to deleting it, yes I have a track log. I'm not sure it
would be very good as the trees meant that I kept losing the signal. We
passed within about 300m of Gasson Farm, but used the Duke of Kent school as
our crossing place between the two sections of Hurt Wood. On the way back,
we crossed at Peaslake. As we had an early start (walking finished by
11:30), so we wouldn't have met at any point.

Quoted message said:

Quoted message said:

If anyone thinks this was easy, let me assure you I would rather navigate
across the Brecons or Snowdonia any time than through Surrey woods. The
woods often have paths not on the map and map paths that do not exist on

the

Quoted message said:

Quoted message said:

ground.

Amen. And the GPS was not a lot of help yesterday thanks to the wet
leaves.

Probably the most trouble I have had getting a signal since I upgraded from
2.10 to 2.50 (or whatever it is) of my Garmin OS.

Have fun,
Paul

"Phil Cook" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Paul Cummings said:

I was out walking the Surrey Hills yesterday (around Holmbury and Pitch
Hills if you want to know).

Oh spooky!

I was doing a loop from Gomshall across to Shere down Ponds Lane
through Hurt Wood and past the Volunteer at Sutton Abinger - lack of
time to get from there to Gomshall Station precluded sampling the ale
:-(

I am finding it more and more difficult to find routes in the 15-25km range
within this area (inc Leith Hill, Box Hill etc) which mostly avoid roads
and built up areas, so if you have any, I would be very grateful.

Quoted message said:

Do you have a GPS track log by any chance? Looking at mine I see we
were in Hurt Wood from about 14:00 and passed Gasson Farm at 14:30.

Until I get around to deleting it, yes I have a track log. I'm not sure it
would be very good as the trees meant that I kept losing the signal. We
passed within about 300m of Gasson Farm, but used the Duke of Kent school as
our crossing place between the two sections of Hurt Wood. On the way back,
we crossed at Peaslake. As we had an early start (walking finished by
11:30), so we wouldn't have met at any point.

Quoted message said:

Quoted message said:

If anyone thinks this was easy, let me assure you I would rather navigate
across the Brecons or Snowdonia any time than through Surrey woods. The
woods often have paths not on the map and map paths that do not exist on

the

Quoted message said:

Quoted message said:

ground.

Amen. And the GPS was not a lot of help yesterday thanks to the wet
leaves.

Probably the most trouble I have had getting a signal since I upgraded from
2.10 to 2.50 (or whatever it is) of my Garmin OS.

Have fun,
Paul

"Phil Cook" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Paul Cummings said:

I was out walking the Surrey Hills yesterday (around Holmbury and Pitch
Hills if you want to know).

Oh spooky!

I was doing a loop from Gomshall across to Shere down Ponds Lane
through Hurt Wood and past the Volunteer at Sutton Abinger - lack of
time to get from there to Gomshall Station precluded sampling the ale
:-(

I am finding it more and more difficult to find routes in the 15-25km range
within this area (inc Leith Hill, Box Hill etc) which mostly avoid roads
and built up areas, so if you have any, I would be very grateful.

Quoted message said:

Do you have a GPS track log by any chance? Looking at mine I see we
were in Hurt Wood from about 14:00 and passed Gasson Farm at 14:30.

Until I get around to deleting it, yes I have a track log. I'm not sure it
would be very good as the trees meant that I kept losing the signal. We
passed within about 300m of Gasson Farm, but used the Duke of Kent school as
our crossing place between the two sections of Hurt Wood. On the way back,
we crossed at Peaslake. As we had an early start (walking finished by
11:30), so we wouldn't have met at any point.

Quoted message said:

Quoted message said:

If anyone thinks this was easy, let me assure you I would rather navigate
across the Brecons or Snowdonia any time than through Surrey woods. The
woods often have paths not on the map and map paths that do not exist on

the

Quoted message said:

Quoted message said:

ground.

Amen. And the GPS was not a lot of help yesterday thanks to the wet
leaves.

Probably the most trouble I have had getting a signal since I upgraded from
2.10 to 2.50 (or whatever it is) of my Garmin OS.

Have fun,
Paul

"Dave Fawthrop" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

On Sun, 7 Nov 2004 08:08:34 -0000, "Paul Cummings"
<[email hidden]> wrote:

Not spooky at all. When we look at a map we see everything on it between
where we are and where we want to be. We note and use wood boundaries,
contours everything on the map, not to mention memory of what you saw on
the trip out and other trips in the area. So I suggest that you thought
you were only using only the bearing, but subconsciously corrected your
course, using contours, memory etc. etc. When we were Hunter Gatherers,
we did not have paper maps, but we found our way round quite well.

You might be right, but all the way I was expecting to be 100-200m out.
When I first found the white van, I still expected to be far out, but made
the effort to still keep on my bearing, which proved to be true.

Oh, and by the way, we stopped using the map when we started using the
bearing and neither of us had been over that exact area before (although
both of us had actually been to the start and end points before). I had
certainly never seen the car park from that direction, which is why I did
not recognise it until I was right there.

Maybe I need to try this a few more times to see if it is luck, skill or
just impossible to go far wrong. I still think it was largely luck with
some skill.

Have fun,
Paul

"Dave Fawthrop" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

On Sun, 7 Nov 2004 08:08:34 -0000, "Paul Cummings"
<[email hidden]> wrote:

Not spooky at all. When we look at a map we see everything on it between
where we are and where we want to be. We note and use wood boundaries,
contours everything on the map, not to mention memory of what you saw on
the trip out and other trips in the area. So I suggest that you thought
you were only using only the bearing, but subconsciously corrected your
course, using contours, memory etc. etc. When we were Hunter Gatherers,
we did not have paper maps, but we found our way round quite well.

You might be right, but all the way I was expecting to be 100-200m out.
When I first found the white van, I still expected to be far out, but made
the effort to still keep on my bearing, which proved to be true.

Oh, and by the way, we stopped using the map when we started using the
bearing and neither of us had been over that exact area before (although
both of us had actually been to the start and end points before). I had
certainly never seen the car park from that direction, which is why I did
not recognise it until I was right there.

Maybe I need to try this a few more times to see if it is luck, skill or
just impossible to go far wrong. I still think it was largely luck with
some skill.

Have fun,
Paul

"Dave Fawthrop" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

On Sun, 7 Nov 2004 08:08:34 -0000, "Paul Cummings"
<[email hidden]> wrote:

Not spooky at all. When we look at a map we see everything on it between
where we are and where we want to be. We note and use wood boundaries,
contours everything on the map, not to mention memory of what you saw on
the trip out and other trips in the area. So I suggest that you thought
you were only using only the bearing, but subconsciously corrected your
course, using contours, memory etc. etc. When we were Hunter Gatherers,
we did not have paper maps, but we found our way round quite well.

You might be right, but all the way I was expecting to be 100-200m out.
When I first found the white van, I still expected to be far out, but made
the effort to still keep on my bearing, which proved to be true.

Oh, and by the way, we stopped using the map when we started using the
bearing and neither of us had been over that exact area before (although
both of us had actually been to the start and end points before). I had
certainly never seen the car park from that direction, which is why I did
not recognise it until I was right there.

Maybe I need to try this a few more times to see if it is luck, skill or
just impossible to go far wrong. I still think it was largely luck with
some skill.

Have fun,
Paul

I noticed that Message-ID: <[email hidden]> from Paul
Cummings contained the following:

Quoted message said:

You might be right, but all the way I was expecting to be 100-200m out.

Check my script. You'd have to be very inaccurate to be that far out.

http://www.ckdog.co.uk/test/bearing_error.php
--
Geoff Berrow (put thecat out to email)
It's only Usenet, no one dies.
My opinions, not the committee's, mine.
Simple RFDs http://www.ckdog.co.uk/rfdmaker/

Paul Cummings said:

"Phil Cook" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Paul Cummings said:

I was out walking the Surrey Hills yesterday (around Holmbury and Pitch
Hills if you want to know).

Quoted message said:

I am finding it more and more difficult to find routes in the 15-25km range
within this area (inc Leith Hill, Box Hill etc) which mostly avoid roads
and built up areas, so if you have any, I would be very grateful.

A long time ago I bought the Pathfinders TQ00/10 50 and TQ00/10 40 and
just make things up as I go along. That circular from Gomshall is a
favourite I've done it lots of times but never clockwise. There are
all sorts of routes up and down the Downs taking in bits of the North
Downs Way

Quoted message said:

Quoted message said:

Do you have a GPS track log by any chance? Looking at mine I see we
were in Hurt Wood from about 14:00 and passed Gasson Farm at 14:30.

Until I get around to deleting it, yes I have a track log. I'm not sure it
would be very good ...

Lots of gaps in mine and one. The section along the track in Hurt Wood
was about 150m out running parallel.

Quoted message said:

we wouldn't have met at any point.

Ah well. Mine was a late finishing affair, it was dark by the time we
got to Gomshall station.

Quoted message said:

Probably the most trouble I have had getting a signal since I upgraded from
2.10 to 2.50 (or whatever it is) of my Garmin OS.

I blame the rain. I have an almost perfect track from a walk over a
nearly identical route done in August.
--
Phil Cook looking north over the park to the "Westminster Gasworks"

"Phil Cook" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Paul Cummings said:

"Phil Cook" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

On Sun, 7 Nov 2004 08:08:34 -0000, Paul Cummings wrote:

>I was out walking the Surrey Hills yesterday (around Holmbury and

Pitch

Quoted message said:

Quoted message said:

Quoted message said:

>Hills if you want to know).

Quoted message said:

I am finding it more and more difficult to find routes in the 15-25km

range

Quoted message said:

Quoted message said:

within this area (inc Leith Hill, Box Hill etc) which mostly avoid roads
and built up areas, so if you have any, I would be very grateful.

A long time ago I bought the Pathfinders TQ00/10 50 and TQ00/10 40 and
just make things up as I go along. That circular from Gomshall is a
favourite I've done it lots of times but never clockwise. There are
all sorts of routes up and down the Downs taking in bits of the North
Downs Way

I have quite a nice route I do from Gomshall to Chilworth station. Comes in
at just over 20km and covers a lot of nice ground in a linear walk. Other
than that, I am really starting to stretch. I've done a few Holmwood
Station to Box Hill station via Leith Hill walks and have a Box Hill
Highlights that comes out at 17km, but otherwise I struggle to get the
distance in with out walking around roads or through really boring lands.

I hear Brecon calling me.... Actually it will probably be Abergavenny next
time as I want to finish off a lot of minor peaks around there (mostly the
sub 2000' Marilyns).

Have fun,
Paul