New Great Circle Maps

[Pete]

I've been teaching myself a fair bit about great cirlces recently (ie, the shortest distance between two points on a globe, which follows the "great circle" as if you were cutting a line between the two points and the center of the Earth). The maths gets a bit hairy at times, and advanced trig wasn't really my strongest point at school, but my first project has been to create new Great Circle Maps for the Itineraries forum.

I've tried to improve a little on the original maps, which came from the fantastic resource that is the Great Circle Map at gc.kls2.com. I've started with a large (3750 x 2250) version of the 'Blue Marble' NASA image of the Earth, which I personally think is amazing. The application behind the map then works out where the two points on the map are and crops and scales the image around that. It then works out the Great Cirlce path and plots that across the map, taking into account the crop & scale. Finally it also writes in the distance in miles between the two points.

Currently, in this beta form, it only accepts two points (the gc.kls2.com mapper can take any number), so I'm reverting to the original kls2 maps where there are more than two points or where one of the points cannot be found in the internal Airport database.

Have a poke around in the Intinerary forum for some examples, and feel free to ask any geeky questions about this very dry subject while the maths is still spinning around in my head...

Pete

[Scrooge]

Thanks for updating that and of course keeping the whole site running for us.

Just one thing though,could you post that in English for me please

Cool, thanks Pete.

Cheers

Edited to not look like an idiot [:I].

[Pete]

Originally posted by sean modi
Cool, thanks Pete, I think my flight I just posted here is a good example.

Cheers

Hmmm... not such a good example, as that's a "via" route, which defaults back to the original mapper. I haven't yet expanded the "Blue Marble Mapper" (as henceforce I've decided it's too be called ) to more than two locations.

Pete

Originally posted by pixuk

Originally posted by sean modi
Cool, thanks Pete, I think my flight I just posted here is a good example.

Cheers

Hmmm... not such a good example, as that's a "via" route, which defaults back to the original mapper. I haven't yet expanded the "Blue Marble Mapper" (as henceforce I've decided it's too be called ) to more than two locations.

Pete

I'm with you now, I'm not too good with computer language [:I].

[Pete]

Originally posted by jetwet1

Just one thing though,could you post that in English for me please

Since you asked...

Unless you're a paid-up member of the Flat Earth Society, you're probably aware that the Earth is a globle. It's not quite a perfect sphere (it bulges ever so slightly around the middle), but for the purposes of simple explanation, let's ignore that for a moment.

The closest distance between two points on the earth's surface can be found by slicing the globe in 2, through the centre, with the 2 points on the edge. This is called the Great Circle.

When you look at a 2D map of the world, obviously things have been flattened out, and you can't just draw a straight line between two points to find the shortest distance. The 'Great Circle' will arc up or down (depending on which side of the equator you are). You can demonstrate that for yourself if you have a Globle. Hold a piece of string from London to LAX, and you'll see it crosses the bottom of Greenland rather than going straight across the Atlantic and over New York (which is what a flat representation of the globe would suggest is the shortest route).

So, the map widget thingy that I've been spending way too much time on for the last couple of days does three things;

1. Establish where the two points given are on the flat map, and crop and scale the large version of the map to those points (with a small margin)
2. Works out the Great Circle route from point A - B and draws that on the map
3. Finally, works out the distance in miles between A & B, and writes that into the graphic.

Simple as a quadratic equation...

Pete

[Scrooge]

I now have a headache !

Seriously though as a flight sim nerd I know what the great circle is,just wondering how it works with "blue marble though"

[Pete]

Originally posted by sean modi

Originally posted by pixuk

Originally posted by sean modi
Cool, thanks Pete, I think my flight I just posted here is a good example.

Cheers

Hmmm... not such a good example, as that's a "via" route, which defaults back to the original mapper. I haven't yet expanded the "Blue Marble Mapper" (as henceforce I've decided it's too be called ) to more than two locations.

Pete

I'm with you now, I'm not too good with computer language [:I].

Your flight here is a better example

[Scrooge]

Just took a look at that,I don;t care how it works,that looks sweet,maybe you should drop MS a line and see if they want to use it for the next addition of MSFS?

[Pete]

Originally posted by jetwet1
I now have a headache !

Seriously though as a flight sim nerd I know what the great circle is,just wondering how it works with "blue marble though"

The 'Blue Marble' is NASAs fantastic project to map the whole globe, details here

Pete

[Pete]

I've tweaked the forum code so you can drop a Blue Marble Map into any of your posts using a standard code block;

So... {map}LHR-JFK{/map} (replacing those curly brackets with square ones!) produces;

Great Job , looks great. Now if only VS would 'fly the line' we might get there a little quicker:D

Great work Pix!

Could these be added by default to TR's too?

It would be especially handy for the "other airlines" section, where I am not familiar with the airport codes.

Cheers.

Rich.

[Pete]

Potentially - if the subject line follows the standard format, I could extract the route info from that.

Pete

[Pete]

Ok, 'tis done.

Pete

Originally posted by pixuk
Ok, 'tis done.

Pete

Excellent work - and done in speedy time too!

Thanks Pix!

[preiffer]

Great stuff Pete - they look good.

Just one little niggly thing - they seem to push the page out by about 10px to the right? (just *slightly* too big?)

This thread is an example in itself, and so is this one.

I don't know if it's because of my massive screen resolution, but I can't see a difference in the width.

[preiffer]

Try page 1, Nick

Ehh, still really can't see one, if at all, it's about 5 pixels. I'm not complaining. [:p]