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Great Circle Mapper  
User currently offlineBA From United States of America, joined May 2000, 11153 posts, RR: 59
Posted (10 years 3 months 3 weeks 3 days 16 hours ago) and read 4754 times:

I'm sure many of you know the Great Circle Mapper website:
http://gc.kls2.com

I was wondering if this excellent program takes into account the fact that the Earth is an oblate spheroid? Or does it consider the Earth to be a perfect sphere?

Just wondering to get an idea about its accuracy.

Regards


"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran
8 replies: All unread, jump to last
 
User currently offlineScottysAir From , joined Dec 1969, posts, RR:
Reply 1, posted (10 years 3 months 3 weeks 3 days 16 hours ago) and read 4733 times:

BA,

This is very good website of the Great Circle Mapper. I am sure you can do it for yourself. Sometimes, when I am use with their website on The Gret Circle Mapper.


User currently offlineVirginFlyer From New Zealand, joined Sep 2000, 4575 posts, RR: 41
Reply 2, posted (10 years 3 months 3 weeks 6 hours ago) and read 4548 times:

BA - perhaps it would be worth email the site's owner and asking - his email address is given on the bottom of the page...

V/F



"So powerful is the light of unity that it can illuminate the whole earth." - Bahá'u'lláh
User currently offlineLY7E7 From Israel, joined Jun 2004, 2259 posts, RR: 19
Reply 3, posted (10 years 3 months 2 weeks 6 days 22 hours ago) and read 4459 times:

was wondering if this excellent program takes into account the fact that the Earth is an oblate spheroid?

Although that is a great software I really doubt that that is the case. In order to take in account the Geoid (i.e. using a certain datum for the calculations) there is a need for a professional GIS infrastructure. If such was used I guesss we all would be paying for the GCM.

Still , a very good application, I use it a lot.

Regards.



2 things are endless: ignorance and space
User currently offlineTimz From United States of America, joined Sep 1999, 6873 posts, RR: 7
Reply 4, posted (10 years 3 months 2 weeks 6 days 7 hours ago) and read 4299 times:

As he explains, the Mapper uses the Clarke 1866 spheroid, which isn't the right one nowadays, but it seems to give distances correct within a small fraction of a kilometer. If he used a sphere the calculated distances would occasionally be off by 10 km or more.

User currently offlineArcano From Chile, joined Mar 2004, 2409 posts, RR: 23
Reply 5, posted (10 years 3 months 2 weeks 6 days 4 hours ago) and read 4215 times:

Look how it draws the route SCL-SYD:



If it considered the Earth as a perfect sphere, why going down instead of suggesting a stright line across the pacific?
The software recognize thant the best route is going down, so it realizes the Earth is not a sphere!



Regards



in order: 721,146,732,763,722,343,733,320,772,319,752,321,88,83,744,332,100,738, 333, 318, 77W, 78, 773 and 380
User currently offlineBA From United States of America, joined May 2000, 11153 posts, RR: 59
Reply 6, posted (10 years 3 months 2 weeks 5 days 21 hours ago) and read 4127 times:

Thanks for all the replies.

If it considered the Earth as a perfect sphere, why going down instead of suggesting a stright line across the pacific?

A straight line across the Pacific would be the shortest distance if the Earth were perfectly flat.

However, since the Earth is a sphere, you cannot truly get an accurate drawing unless you draw it on a 3D model of the Earth. However, to simulate the sphere of the Earth, we draw the line curved, following the true path.

Take an orange, draw a line across it somewhere. Peel the orange carefully, and lay the peel flat and you will see that your line appears flat, taking a southernly or northernly course.

My suggestion also is you take a globe, and use a string and connect two points and experiment around with different routings, you will see what the shortest route is.

Regards



"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran
User currently offlineTimz From United States of America, joined Sep 1999, 6873 posts, RR: 7
Reply 7, posted (10 years 3 months 2 weeks 5 days 12 hours ago) and read 4002 times:

Take this example: use the Mapper to get the distance from ANC to LED; it says 6587 km. If they were using a sphere, that would imply a radius of 6394 km, based on the lat-lons they give. But if you try HNL-RAR, they give a distance of 4708 km, which implies a radius of 6338 km. So they're not using a sphere.

User currently offlineTOLtommy From United States of America, joined Dec 2003, 3299 posts, RR: 4
Reply 8, posted (10 years 3 months 2 weeks 5 days 10 hours ago) and read 3952 times:

"I was wondering if this excellent program takes into account the fact that the Earth is an oblate spheroid?"

I'm pretty sure it did, but the name "Great Oblate Spheriod Mapper" just didn't have the same sex appeal. Darn those marketing people!  Nuts



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