An accurate center of gravity calculator for Google Earth is now available here. All the code is Brammeleman‘s, taken from his calculator page here, save for the one final altered latitude correction, which places the center of gravity closer to the poles — at the correct position.

Abbreviated instructions: In Google Earth, collect your placemarks in a folder and save that folder to your hard drive as a KML file (not KMZ). Upload this file into the calculator and open the returned file in Google Earth. Voila.

So what does this center of gravity calculator do, precisely?

Practically speaking, the spot you get back minimizes the total distance people at placemarks will need to travel in order to meet up together. And if you calculate the center of gravity for just two placemarks, the straight line you can draw through all three points will be the shortest distance as the jumbo jet flies between your two placemarks.

Mathematically speaking, the code first finds the center of gravity for given points of equal mass on the surface of a sphere in three dimensional space. (The center of gravity will thus be inside the sphere.) It then finds the point on the sphere closest to the center of gravity by projecting a straight line from the center of the sphere through the center of gravity to the surface of the sphere.

The algorithm assumes Earth is a sphere, even though it is actually a geoid, so errors of tens of meters will persist. Correcting for those is something I am two PhDs short of being able to do.

The original story is three posts down, here. As a result of the correction, my family’s actual center of gravity is now 43km further north, in Bree, near the Dutch border.

This one I hadn’t seen coming: Google Earth and Fiat are cobranding a competition that highlights the Turin Winter Olympics. You register via a slick site, and are then given a network link to download. This takes you to the Olympic area around Turin in Google Earth, which now boasts upgraded high resolution images.

Your task: Pick one of the dots on the map ÇƒÓ any dot will do (it’s not exactly a skills-based competition.) The four people whose dots prove closest to the hidden treasure by the end of the contest will win a New Fiat Sedici 4×4. As the cars cost $20,000 and the competition takes 3 minutes, this one is a no brainer.

While you’re surfing around Turin, why not take advantage of a KML file marking all Olympic venues, posted to Google Earth Community by Gommunity.

(PS. A preference for truth in advertising compells me to note that this competition is not “the first contest that lets you look down on the world from on high.” Don’t forget Adidas.)

(Via Touristime.it)

[Update 2006-02-02: 00:12 UTC: Heh. From the small print: “The Fiat Sedici can be awarded as a prize to contest winners in the following countries: Italy, France, Great Britain, Austria, Switzerland, Greece and Spain.”]

Scrappad reports that ESRI has released its ArcGIS Explorer as a closed beta, which apparently means that scores of GIS pro bloggers will be playing with it without being allowed to blog it due to NDAs. How frustrating has that got to be? :-) Meanwhile, Geography 2.0 provides a non-NDA-constrained overview of ArcGIS Explorer, and how it will likely be positioned against Google Earth.

For NASA World Wind users comes news of an important plugin, Shockfire’s KMLImporter, which does precisely that. I’m on a Mac so I can’t test it, and I doubt it has the functionality of the network link, but this plugin opens a wealth of static content to World Wind users, including 3D objects and overlays found on numerous Google Earth content sites. I’ll be on the lookout for feedback on the usefulness of the plugin. (Here is the developer’s blog.)

The release of KMLImporter is not so important for Google Earth surfers, but it is important for KML content developers, who might soon want to start checking their work in both Google Earth and World Wind — just like how web developers check their work in IE, FireFox, Safari, etc… Let’s hope the geobrowsers manage to avoid the cross-app rendering quirks that have so plagued web browsers. (Via Le Blogue du CFM de Guadalajara)

Two items with a Pacific theme this morning:

It’s always hurricane season somewhere. In the South Pacific, cyclone season opens with Jim, bearing down on this New Caledonian blogger, who’s following it and related webcams in Google Earth with this hurricane tracker, an oldie but good one.

On the other side of the Pacific, Seattle Wireless, a community wifi network, now has a Google Earth network link (KML) to accompany its Google Maps mashup.