Garmin GPS - Where Exactly Is The Equator

Author

Where Exactly Is The Equator

Joel

2007-07-25, 12:33 pm

On my last day in Ecuador, a few days ago, I went on a tour with my
group from Qito to a monument which was established over 100 years ago
for what the scientists then believed was the location of the Ecuador.
Today we know that the monument is a bit too far south.

However, we ALSO visited a place about 1 /4 mile away which had a sign
in front saying that within it was the Equator as determined by GPS.
The bus parked in front and we went in.

They had a line showing the exact location of the equator and were
performing various activities to prove it was the equator. The thing
is I had a iQue 3600 with me and it was locked in to 8 satellites with
a reported error of 25 feet and it said that the line reported as the
equator was actually 3 seconds south of the equator. My iQue reported
the Equator to be in the middle of the road where our bus was parked
outside that property some 100 to 200 yards north.

I asked the owner how could this be and he brought over one of his
'techies' who explained that they measured the equator location with a
military GPS and also my iQue was using the wrong Map datum (the WGS
option they told me they used wasn't even an option on my iQue).

So I have two questions:

1. How is it that my iQue with its margin of error was nowhere near
their reported value? Was the iQue report of the Equator incorrect or
was their depiction of the Equator likely incorrect?
2. I don't know much about map datum but it would seem to me that the
datum I chose would have no impact on the location of the Equator - OR
can the Equator be in a different place based upon the map datum?

By the way, one of the experiments they showed was putting a few
leaves in a pan and then letting the water flow out a hole in the
bottom. The leaf turned one way a few feet on one side of their
'line' and the other way on the other side of the line (and straight
down on the line). I was with a PhD physicist and he said that was a
bunch of hogwash and that the effect is too weak to be meaningful
especially across a few feet - he said it had more to do with the
shape of the pan and the way it was oriented. Which is correct? Is
this rotation thing an old wives tale and if not, can it be used to
pinpoint the exact location within a foot or so of the equator?

Thanks for any feedback in advance,
Joel

Bad Idea

2007-07-25, 10:33 pm

search "critical thinking"

Raoul Watson

2007-07-25, 10:33 pm

"Joel" <askme@forit.com> wrote in message
news:6m0fa3dbkid3one
v6rt1qhikq611ds3f58@
4ax.com...
> On my last day in Ecuador, a few days ago, I went on a tour with my
> group from Qito to a monument which was established over 100 years ago
> for what the scientists then believed was the location of the Ecuador.
> Today we know that the monument is a bit too far south.
>
> However, we ALSO visited a place about 1 /4 mile away which had a sign
> in front saying that within it was the Equator as determined by GPS.
> The bus parked in front and we went in.
>
> They had a line showing the exact location of the equator and were
> performing various activities to prove it was the equator. The thing
> is I had a iQue 3600 with me and it was locked in to 8 satellites with
> a reported error of 25 feet and it said that the line reported as the
> equator was actually 3 seconds south of the equator. My iQue reported
> the Equator to be in the middle of the road where our bus was parked
> outside that property some 100 to 200 yards north.
>
> I asked the owner how could this be and he brought over one of his
> 'techies' who explained that they measured the equator location with a
> military GPS and also my iQue was using the wrong Map datum (the WGS
> option they told me they used wasn't even an option on my iQue).
>
> So I have two questions:
>
> 1. How is it that my iQue with its margin of error was nowhere near
> their reported value? Was the iQue report of the Equator incorrect or
> was their depiction of the Equator likely incorrect?
> 2. I don't know much about map datum but it would seem to me that the
> datum I chose would have no impact on the location of the Equator - OR
> can the Equator be in a different place based upon the map datum?
>
> By the way, one of the experiments they showed was putting a few
> leaves in a pan and then letting the water flow out a hole in the
> bottom. The leaf turned one way a few feet on one side of their
> 'line' and the other way on the other side of the line (and straight
> down on the line). I was with a PhD physicist and he said that was a
> bunch of hogwash and that the effect is too weak to be meaningful
> especially across a few feet - he said it had more to do with the
> shape of the pan and the way it was oriented. Which is correct? Is
> this rotation thing an old wives tale and if not, can it be used to
> pinpoint the exact location within a foot or so of the equator?
>
> Thanks for any feedback in advance,
> Joel

I would venture to say that your GPS is probably more correct :-).
For practical reason, the owner of the land obviously could not have drawn
the line on the public street!

But it is also true about the geodetic system, there are WGS50,60,66,72 and
the latest I think is 84 (I might be wrong). While I am not an expert in
this subject, my understanding is that the meridian did move three hundred
feet or so --but not sure about the equator.

It is true however, that in the northern hemisphere, a draining sink would
spin clockwise and just prior to emptying would inverse the direction to
counter clockwise. While in the southern hemisphere, it would spin
counter-clockwise and at the last second change to clockwise. But I think
this is a different region of physics probably has not been discovered :-)

If we are to accept that this is due to the inertial circles of air masses
(clockwise in northern hemisphere and counterclockwise in the southern),
the physicist is probably correct, the effect of a couple of feet would be
too weak and besides the Corriolist effect probably would not apply to such
small amount of water.

Gerry Snyder

2007-07-26, 4:33 am

Joel wrote:
> ....

>
> By the way, one of the experiments they showed was putting a few
> leaves in a pan and then letting the water flow out a hole in the
> bottom. The leaf turned one way a few feet on one side of their
> 'line' and the other way on the other side of the line (and straight
> down on the line). I was with a PhD physicist and he said that was a
> bunch of hogwash and that the effect is too weak to be meaningful
> especially across a few feet - he said it had more to do with the
> shape of the pan and the way it was oriented. Which is correct?

The physicist was right about the coriolis force being orders of
magnitude too small to show up in the "demonstration" you saw.

I saw something very similar in Kenya, and the sense of rotation of the
water as it flowed out of the container was determined by how the water
was poured in. It's easy to impart angular momentum just by directing
the pouring spout in one direction or the other.

Even though I saw the trick, the young man put on such a good show that
I still gave him a nice tip.

Gerry

Michael Cooper

2007-07-26, 4:33 am

They are probably both correct. As the owner explained, the location of
"the equator" depends entirely on the datum you're using.

To determine precisely where the equator is, you need a very precise
defintion of *what* the equator is. Since the earth is usually modeled
as an ellipsoid of some sort, the most obvious definition is the
"waist" of the ellipsoid. The actual location of the waist depends
quite sensitively on the parameters which define the size and
orientation of the ellipsoid used to approximate the earth. These
parameters differ slightly from datum to datum.

All datums assume more or less the same shape and orientation for the
earth, but these parameters are tweaked so that the ellipsoid matches
the actual surface of the earth as well as possible in a particular
area.

For example, here in Canada we commonly use two different datums for
mapping: NAD27 and NAD83. The UTM northing of a point can easily move
by 100 metres going from one to the other. This means that the distance
from the equator to that point changes by 100 metres, even though the
point itself does not move. That's because the two datums make slighly
different assumptions about the size and orientation of the earth, and
therefore the location of the equator.

Although a lot of work is done using the WGS84 datum these days, there
are still a tremendous number of local datums in use. It's entirely
possible that the people who measured the location of "the equator"
were measuring the location of a different equator than you were.

Michael

On 2007-07-25 11:17:25 -0600, Joel <askme@forit.com> said:

> 1. How is it that my iQue with its margin of error was nowhere near
> their reported value? Was the iQue report of the Equator incorrect or
> was their depiction of the Equator likely incorrect?
> 2. I don't know much about map datum but it would seem to me that the
> datum I chose would have no impact on the location of the Equator - OR
> can the Equator be in a different place based upon the map datum?

Joel

2007-07-26, 12:33 pm

Thanks - that was an awesome explanation - the best I have seen. I
hadn't realized the impact the datums had on the location of the
Equator. When I was there, the techie told me the datum they used at
it was a WGS with a number larger than the two on my datum list (WGS
72 & 84). There was also no choice for Ecuador so I could not figure
out how to change to match what they used.

In this day and age of satellites and GPSs, Its a shame that we can't
get all the countries on the Equator to agree exactly where it is.

Joel
[color=darkred]
>They are probably both correct. As the owner explained, the location of
>"the equator" depends entirely on the datum you're using.
>
>To determine precisely where the equator is, you need a very precise
>defintion of *what* the equator is. Since the earth is usually modeled
>as an ellipsoid of some sort, the most obvious definition is the
>"waist" of the ellipsoid. The actual location of the waist depends
>quite sensitively on the parameters which define the size and
>orientation of the ellipsoid used to approximate the earth. These
>parameters differ slightly from datum to datum.
>
>All datums assume more or less the same shape and orientation for the
>earth, but these parameters are tweaked so that the ellipsoid matches
>the actual surface of the earth as well as possible in a particular
>area.
>
>For example, here in Canada we commonly use two different datums for
>mapping: NAD27 and NAD83. The UTM northing of a point can easily move
>by 100 metres going from one to the other. This means that the distance
>from the equator to that point changes by 100 metres, even though the
>point itself does not move. That's because the two datums make slighly
>different assumptions about the size and orientation of the earth, and
>therefore the location of the equator.
>
>Although a lot of work is done using the WGS84 datum these days, there
>are still a tremendous number of local datums in use. It's entirely
>possible that the people who measured the location of "the equator"
>were measuring the location of a different equator than you were.
>
>Michael
>
>On 2007-07-25 11:17:25 -0600, Joel <askme@forit.com> said:
>

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