Postcrossing Official Forum
Not logged in [Login - Register]
Go To Bottom


Printable Version  
Author: Subject: Distance calculation
BITAMIH
New Member
**




Posts: 3
Registered: 28-1-2014
Country Flag:
Sweden

Sweden
Postcrossing Username: BITAMIH
Member Is Offline


[*] posted on 28-1-2014 at 10:57 PM
Distance calculation


I see the system doesn't calculate the shortest distance but just in one direction on the map.
I don't how to explain it but, for example, if the postcard is sent from USA to Australia the distance is calculated across the whole globe though Africa etc. but probably is really sent just through Americas, which can reduce the distance three times, I don't know if I explained it well.
View user's profile View All Posts By User
paulo
Super Administrator
*********


Avatar


Posts: 475
Registered: 28-11-2005
Country Flag:
Portugal

Portugal
Postcrossing Username: paulo
Member Is Offline


[*] posted on 8-2-2014 at 02:33 PM


We use the Haversine formula to calculate great-circle distances between two points on a sphere (not 100% accurate, but good enough for what we do with it). So, it does go with the direction of the shortest path.

Example: take US-2554141 from New York to Melbourne. Our formula says 16,666 km (10,356 miles) which seems about right when measuring it across the pacific (as it should).
View user's profile Visit user's homepage View All Posts By User
Norway_girl
Member
******


Avatar


Posts: 1068
Registered: 6-11-2007
Location: Hønefoss, Norway
Country Flag:
Norway

Norway
Postcrossing Username: Norway_girl
Member Is Offline


[*] posted on 8-2-2014 at 04:32 PM


Interesting to know that it's the great-circle distances that are shown!

Even though the distance of US-2554141 is measured across the pacific, the map still show the travel route as across the Atlantic Ocean, Africa and Indian Ocean. Then it would be easy to think that the given distance is the distance of this line.
View user's profile Visit user's homepage View All Posts By User
paulo
Super Administrator
*********


Avatar


Posts: 475
Registered: 28-11-2005
Country Flag:
Portugal

Portugal
Postcrossing Username: paulo
Member Is Offline


[*] posted on 8-2-2014 at 08:08 PM


That's quite true, the map doesn't show the shortest path. Technically it should be possible to make the line wrap the date line, but I find that that representation (even if more correct) to be more confusing to most people as most are used to see the world map centered differently. Also, on this particular example, a long line over the never ending pacific might make make things a bit confusing since there's less (land) context.

Then again, we never know the actual path a postcard took. Would be fun if we could actually map that - I wonder how many zigzags they actually take and how much more distance they travel in fact :).
View user's profile Visit user's homepage View All Posts By User
Norway_girl
Member
******


Avatar


Posts: 1068
Registered: 6-11-2007
Location: Hønefoss, Norway
Country Flag:
Norway

Norway
Postcrossing Username: Norway_girl
Member Is Offline


[*] posted on 8-2-2014 at 11:02 PM


Quote: Originally posted by paulo  
Technically it should be possible to make the line wrap the date line, but I find that that representation (even if more correct) to be more confusing to most people as most are used to see the world map centered differently.


I have to agree with you on that!

Quote: Originally posted by paulo  

Then again, we never know the actual path a postcard took. Would be fun if we could actually map that - I wonder how many zigzags they actually take and how much more distance they travel in fact :).


Oh, yes, it would for sure be interesting! Especially those postcards that seems to travel "the scenic route" due to teh long time they travel. What about postcards with a GPS chip in it??
View user's profile Visit user's homepage View All Posts By User
dragon27
Member
****


Avatar


Posts: 117
Registered: 3-12-2013
Location: Maryland
Country Flag:
United States

United States
Postcrossing Username: dragon27
Member Is Offline

Mood: First Day of Autumn!

[*] posted on 9-2-2014 at 12:24 AM


Then again, it would need to travel in an envelope. What if it passed through an x-ray on airport cargo? Good idea though!
View user's profile View All Posts By User
paulo
Super Administrator
*********


Avatar


Posts: 475
Registered: 28-11-2005
Country Flag:
Portugal

Portugal
Postcrossing Username: paulo
Member Is Offline


[*] posted on 9-2-2014 at 10:30 AM


We talked about something similar (although, not a postcard) not so long ago on the blog: http://www.postcrossing.com/blog/2013/04/11/what-does-a-trip-throug...
View user's profile Visit user's homepage View All Posts By User

  Go To Top

Imprint