checking the exact distance

What is the best way to check the exact distance between a laptop and a
router? I have tried using a GPS device but it is not very accurate. I
assume there isn't a software program that does this -- since it's very
hardware related. Is there some other device that could tell me -- it would
be through walls and even down the street to find out.

On Wed, 30 Nov 2005 10:49:01 -0600, "JB"
<(E-Mail Removed)> wrote:

>What is the best way to check the exact distance between a laptop and a
>router? I have tried using a GPS device but it is not very accurate. I
>assume there isn't a software program that does this -- since it's very
>hardware related. Is there some other device that could tell me -- it would
>be through walls and even down the street to find out.

Are you measuring inches, feet, or miles? Different methods are used
for each. Inches are best done with a pocket tape measure. Feet can
be done with either a bigger measuring tape, or perhaps a binocular
distance measuring device. Miles are best done with a map.

As far as I know, there's no easy way to use the latency in the
hardware to measure distance accurately. I worked on a project that
did something like that in an attempt to measure how far away the
client radio was from the access point. The idea was to limit users
of a wireless hot spot to only those users located on premisis and to
block any of the nearby apartment users who just wanted a free
broadband connection. It worked, but was deemed to expensive and too
unreliable to be useable.

Incidentally, wireless doesn't really go through walls that well. It
goes through cracks in the walls and bounces around quite a bit. Using
the RF path delay to measure distance in such a reflective environment
is not a great idea.
--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"JB" <(E-Mail Removed)> wrote:
>What is the best way to check the exact distance between a laptop and a
>router?

Well, if you had a wire, a TDR or other network tester would tell you,
but in the wireless world you don't actually care what the _distance_
is, you care what the path loss is, plus any noise/interference.

Why do you want to know the exact distance?

"Jeff Liebermann" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Wed, 30 Nov 2005 10:49:01 -0600, "JB"
> <(E-Mail Removed)> wrote:
>
>>What is the best way to check the exact distance between a laptop and a
>>router? I have tried using a GPS device but it is not very accurate. I
>>assume there isn't a software program that does this -- since it's very
>>hardware related. Is there some other device that could tell me -- it
>>would
>>be through walls and even down the street to find out.

> or perhaps a binocular distance measuring device.

Now that does sound cool, I may check into that.

JB <(E-Mail Removed)> wrote:
> "Jeff Liebermann" <(E-Mail Removed)> wrote in message
> > or perhaps a binocular distance measuring device.

> Now that does sound cool, I may check into that.

Those are a little bit expensive.
Much cheaper are little viewers for judging the distance to a golf pin.
It relies on having a known height pole at the point being measured, but it
might work for you.

http://www.radioshack.com
Digital Golf Scope Reg.: $39.99 You save: -$20.00 $19.99

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5

On Wed, 30 Nov 2005 16:33:27 -0600, "JB"
<(E-Mail Removed)> wrote:

>
>"Jeff Liebermann" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed).. .
>> On Wed, 30 Nov 2005 10:49:01 -0600, "JB"
>> <(E-Mail Removed)> wrote:
>>
>>>What is the best way to check the exact distance between a laptop and a
>>>router? I have tried using a GPS device but it is not very accurate. I
>>>assume there isn't a software program that does this -- since it's very
>>>hardware related. Is there some other device that could tell me -- it
>>>would
>>>be through walls and even down the street to find out.
>
>> or perhaps a binocular distance measuring device.

>Now that does sound cool, I may check into that.

Well, the cheap ones are at the golf shop. It's just a scale that
measures the height of the "pin" that holds the flag in the hole.

Parallax distance measuring binoculars are useless beyond about
1000ft. If you can increase the baseline to something wider, then you
can use these to measure farther. WWI battleships had a 12ft baseline
optical range finder. If you have lots of money, a laser range finder
works really nice. If you only want to go a few feet, ultrasonic
digital measuring tapes are cheap.

http://range-finders.binoculars.com


--
Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
831.336.2558 voice
http://www.LearnByDestroying.com AE6KS
http://802.11junk.com Skype: JeffLiebermann
(E-Mail Removed) (E-Mail Removed)

Jeff Liebermann wrote:

> On Wed, 30 Nov 2005 10:49:01 -0600, "JB"
> <(E-Mail Removed)> wrote:
>
>>What is the best way to check the exact distance between a laptop and a
>>router? I have tried using a GPS device but it is not very accurate. I
>>assume there isn't a software program that does this -- since it's very
>>hardware related. Is there some other device that could tell me -- it
>>would be through walls and even down the street to find out.
>
> Are you measuring inches, feet, or miles? Different methods are used
> for each. Inches are best done with a pocket tape measure. Feet can
> be done with either a bigger measuring tape, or perhaps a binocular
> distance measuring device. Miles are best done with a map.

Well, I'm wondering about his GPS. These days anything more than a few feet
_is_ generally done best with a GPS.
>
> As far as I know, there's no easy way to use the latency in the
> hardware to measure distance accurately.

Since that's exactly what a GPS does, even if you had the software I can't
see it being more precise that the GPS he's already failed to get accurate
numbers from.
--
derek

On Thu, 01 Dec 2005 09:49:13 -0400, Derek Broughton
<(E-Mail Removed)> wrote:

>Jeff Liebermann wrote:
>
>> On Wed, 30 Nov 2005 10:49:01 -0600, "JB"
>> <(E-Mail Removed)> wrote:
>>
>>>What is the best way to check the exact distance between a laptop and a
>>>router? I have tried using a GPS device but it is not very accurate. I
>>>assume there isn't a software program that does this -- since it's very
>>>hardware related. Is there some other device that could tell me -- it
>>>would be through walls and even down the street to find out.
>>
>> Are you measuring inches, feet, or miles? Different methods are used
>> for each. Inches are best done with a pocket tape measure. Feet can
>> be done with either a bigger measuring tape, or perhaps a binocular
>> distance measuring device. Miles are best done with a map.
>
>Well, I'm wondering about his GPS. These days anything more than a few feet
>_is_ generally done best with a GPS.

It really depends on the accuracy desired. When I do a coverage map
using Radio-Mobile software:
http://www.cplus.org/rmw/english1.html
I'm often tempted to use my hand held GPS for locating the site. That
never works because GPS alone just isn't accurate enough. When a
tower is located on top of a slope (all too common), a slight error in
GPS location and the calcs end up using a location that's on the side
of the hill instead of the top. Usually, what I end up doing is going
to a web site with topo maps:
http://www.topozone.com
and extracting the location from the map instead of from the GPS. This
also avoids the problem of different datums. There's quite a bit on
handheld GPS location accuracy under the various Geocaching web sites:
http://www.geocaching.com
http://www.geocaching.com/links/
You can really see the problem on the Confluence web site:
http://www.confluence.org
where users post pictures of the integer values of latitude and
longitude. We have a local confluence near the edge of a local golf
course. My guess is that the various photographs over the years cover
about an 800ft error radius for finding the exact location. Yech.

When I really need position accuracy for GPS, I use a data logger and
software that averages the lat-long over about an hour. I use Visual
GPS XP:
http://www.visualgps.net/VisualGPS/ (free)
http://www.visualgps.net/VisualGPSXP/ ($25)
I can usually interpolate the location to within about 1ft radius
after about an hour.

Anyway, if the OP is measuring path lengths in miles, then a few feet
inaccuracy isn't going to make much difference in the calculated path
length. However, if it's a much smaller distance, then accuracy
rapidly becomes a problem.

While I'm ranting on the subject, I've tried WAAS GPS receivers and
found some improvement in accuracy. I'm not sure if it's much of a
help as most of the errors come from reflections. We have a local
differential GPS transmitter on a mountain top, which really improves
the accuracy. Unfortunately, it doesn't cover some of the obscure
areas I need. I've been thinking of setting up my own DGPS system
(yet another project that will never happen). I tried Omnistar
correction service:
http://www.omnistar.com
which provided amazing accuracy, but costs $800/yr plus hardware. I've
also tried a service that differentially corrects locations from
recorded data as used by the surveyors (forgot name). That works
really nice but also costs money.

>> As far as I know, there's no easy way to use the latency in the
>> hardware to measure distance accurately.

>Since that's exactly what a GPS does, even if you had the software I can't
>see it being more precise that the GPS he's already failed to get accurate
>numbers from.

Measuring the route trip delay (latency) is NOT the way a GPS works.
GPS works by measuring the doppler shift and then using spherical
geometry to arrive at a solution.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann <(E-Mail Removed)> wrote:
> You can really see the problem on the Confluence web site:
> http://www.confluence.org
> where users post pictures of the integer values of latitude and
> longitude. We have a local confluence near the edge of a local golf
> course. My guess is that the various photographs over the years cover
> about an 800ft error radius for finding the exact location. Yech.

Other than interference from trees, I would expect that your GPS location
should be within 20 feet if you let the GPS sit in one spot for a few
minutes.

That 800 foot error would have to be due to rugged terrain or user
laziness. My confluence in Mongolia was visited a couple of years later,
and the second visitor is within a couple of feet of my little pile of
rocks, which I put a few feet away from where I meant to put it.
http://www.confluence.org/confluence.php?visitid=8914
I relied on the direction arrow, which starts flitting around when you get
to the spot, and didn't think to switch to the location display until after
I left ;-(

Oh, trees! Your http://www.confluence.org/confluence.php?id=62 is in an
area so heavily covered by trees that a couple of the visitors commented
that they couldn't get a GPS lock near the confluence. I'll have to take
your word for it that those pictures aren't all of the same tree ;-)


Generally, I rely on the GPS to get me to within visual distance of some
desired spot. I was able to locate a gate in a long fence in pitch black
darkness with a GPS waypoint. Trying to find the corners of my property
worked well, but I was looking for existing markers. Trying to note the
exact angle of my house for a solar installation by plotting all four
corners leaves me with a rather lumpy looking house.

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5

Jeff Liebermann wrote:

>>Since that's exactly what a GPS does, even if you had the software I can't
>>see it being more precise that the GPS he's already failed to get accurate
>>numbers from.
>
> Measuring the route trip delay (latency) is NOT the way a GPS works.
> GPS works by measuring the doppler shift and then using spherical
> geometry to arrive at a solution.

Of course, you're right - there's no round trips to a GPS satellite.
However, measuring a doppler shift should be even more accurate. I _still_
can't see how, for any significant distance, he can get more accurate than
his GPS.

I have to admit though, that my GPS experience is with marine systems - we
never have to worry about the hills :-)
--
derek