Path: utzoo!dciem!dretor!chk
From: chk@dretor.dciem.dnd.ca (C. Harald Koch)
Newsgroups: can.uucp
Subject: Re: please clean up your uucp map forms
Message-ID: <1340@dretor.dciem.dnd.ca>
Date: 4 Jan 89 18:11:48 GMT
Article-I.D.: dretor.1340
References: <89Jan3.211712est.38118@neat.ai.toronto.edu>
Reply-To: chk@dretor.dciem.dnd.ca (C. Harald Koch)
Distribution: can
Organization: NTT Systems, Inc., Toronto, Canada
Lines: 65

In article <89Jan3.211712est.38118@neat.ai.toronto.edu> rayan@ai.toronto.edu (Rayan Zachariassen) writes:
[ lots of stuff ]
>- if you don't know your latitude/longitude, try interpolating based on
>  nearby UUCP sites, or ask your local library, airport, or city hall.
>  (I have heard interesting stories of people's reactions when asked
>     "Where are you?" or "Where am I?", so don't get discouraged!)

Other solutions: Obtain a GPS receiver and ask it where you are while standing
next to your computer. (GPS = Global Positioning System, a US military
satellite system for accurate positioning data.)

Here is a way to find a rough approximation:

Find the latitude/longitude of a known reference point that you can locate
on a local map. For Toronto, there is a post at the northeast corner of the
Sanford Fleming building at UofT. This is close enough to the intersection
of King's College Rd. and King's College Circle for measuring purposes.
(Can someone at UofT run outside and find the coordinates of this post for
me?)

Measure the (x,y) distance from the known reference point to your location
along an East-West line and a North-South line. (i.e. The CDF computer room
is about 100m south and perhaps 70m west of this reference point.

Using simple trig, and the fact that the average radius of the Earth is
6,371,225 meters, we find that the circumference of the earth is 40,031,587
meters, and thus there are rougly 30 meters to each second of latitude (the
North-South measurement).

Given the angle of latitude of your location, you can find the ratio of distance
to seconds of latitude as:

	2 * pi * 6371225 * cos(latitude)
	--------------------------------
	      1296000 (= 360 * 60 * 60, the circumference in seconds)

This gives a ratio in meters/second (boy, are we moving fast now!) Around here,
this is (very roughly!!) 22 meters/second.

Now, convert the distances you measured into offsets from the known location
to your location (in seconds). Add these to the coordinates of the known 
location. Tahdah! Instant reasonably accurate position information for your
site.

If you want to get fancy, you can find the location the center of your building,
say, and then give slightly corrected offsets for all the machines on your
building. But this, of course, is plain silly. :-)

If any mathematicians feel like jumping all over my reasoning here, go right
ahead. I never took R&F.

NOTE: This method is inaccurate for long distances!!!! This is due to the
errors introduced when you project the surface of a sphere onto a flat map.
I have seen maps that have aspect ratio corrections for various areas (We
have one on the wall outside the library here at DCIEM), but these are rare
(and expensive...).

--
C. Harald Koch		NTT Systems, Inc., Toronto, Ontario
chk@zorac.dciem.dnd.ca, chk@gpu.utcs.toronto.edu, chk@chkent.UUCP
"I give you my phone number. If you worry, call me. I'll make you happy."