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SirPoonga Geocacher
Joined: 07 Feb 2003
Posts: 144

Posted: Wed Jun 09, 2004 10:23 pm Post subject: calculating distance 


I need to know how to calculate the distance between two waypoints, mathematically. I want to program something and need to know the mathematics behind it. I know it isn't simple because the somewhat spherical shape of the earth. I am having a hard time finding resources. 

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rickrich Geocacher
Joined: 06 Jul 2003
Posts: 673

Posted: Thu Jun 10, 2004 5:32 am Post subject: 


From my "geodist" program at http://geo.rkkda.com. This should be good enough for government work. If you want a more accurate answer, check out Gazza's geodetics calculator.
BTW, around Mpls .001 minute is about 1.8m (5.9ft) NS, and 1.3m (4.26 feet) EW.
Code: 
#
# Rough calculation of distance on an ellipsoid
#
calc_dist_meters() {
awk \
v LATmin=$1 \
v LONmin=$2 \
v LATmax=$3 \
v LONmax=$4 \
'
function calcR(lat)
{
lat = lat * M_PI_180
sc = sin(lat)
x = A * (1.0  E2)
z = 1.0  E2 * sc * sc
y = z ^ 1.5
r = x / y
return r * 1000.0
}
function asin(x) { return atan2(x,(1.x^2)^0.5) }
function dist(lat1, lon1, lat2, lon2,
radiant, dlon, dlat, a1, a2, a, sa, c)
{
radiant = M_PI_180
dlon = radiant * (lon1  lon2);
dlat = radiant * (lat1  lat2);
a1 = sin(dlat / 2.0)
a2 = sin (dlon / 2.0)
a = (a1 * a1) + cos(lat1 * radiant) * cos(lat2 * radiant) * a2 * a2
sa = sqrt(a)
if (sa <= 1.0)
c = 2 * asin(sa)
else
c = 2 * asin(1.0)
return (Ra[int(100 + lat2)] + Ra[int(100 + lat1)]) * c / 2.0;
}
BEGIN {
A = 6378.137
E2 = 0.081082 * 0.081082
M_PI = 3.14159265358979323846
M_PI_180 = M_PI / 180.0
# Build array for earth radii
for (i = 100; i <= 100; i++)
Ra[i+100] = calcR(i)
d = dist(LATmin, LONmin, LATmax, LONmax)
printf "%d\n", d
}
'
}



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sui generis Past MnGCA Board
Joined: 17 Apr 2004
Posts: 608

Posted: Thu Jun 10, 2004 5:44 am Post subject: 


....did you remember to carry the 1? _________________ I am amazed by how many people harp on the need to speak and write English in this country while exhibiting a fundamental lack of skills in the areas of spelling and sentence composition. Would this be irony, hypocrisy, or both? 

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SirPoonga Geocacher
Joined: 07 Feb 2003
Posts: 144

Posted: Sun Jun 13, 2004 10:07 pm Post subject: 


rick, I ggotta find the link to your site again, I know if I look around here enough I will find it. Do you have the source available for your programs? I have a tbug idea and I am working on a way to track how the tbugs spread using svg like gps visualizer. But I to know/figure out the algorithms used to figure out what size of map to use, etc..... 

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Marsha and Silent Bob Past MnGCA President
Joined: 02 Sep 2003
Posts: 6261

Posted: Mon Jun 14, 2004 5:30 am Post subject: 


SirPoonga wrote: 
rick, I ggotta find the link to your site again, I know if I look around here enough I will find it. Do you have the source available for your programs? I have a tbug idea and I am working on a way to track how the tbugs spread using svg like gps visualizer. But I to know/figure out the algorithms used to figure out what size of map to use, etc..... 
http://mngca.rkkda.com/
Yeah the source is there too. _________________ Sad state of affairs. 

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