[eigen] southern hemisphere support in the Geometry module? |

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*To*: eigen <eigen@xxxxxxxxxxxxxxxxxxx>*Subject*: [eigen] southern hemisphere support in the Geometry module?*From*: Benoit Jacob <jacob.benoit.1@xxxxxxxxx>*Date*: Thu, 1 Apr 2010 08:59:30 -0400*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:date:received:message-id :subject:from:to:content-type; bh=FmNVmiq3u/eJPDQdx9tiVIx4V/G3Ts9PyrUwBZz1X3E=; b=dK/qwXKYazOcEmQugUuC3hmTu79I1AxAo4w9zDFhJTIitmolf8sryfjXu1G304fiV3 wIUTEcpylYnI8sG7RlW6XjD3TcqMTL2B0d/FJncCXhXVn41m/XKMRJn8qTc2nsIBdIS0 aM7c45JmDZglQjk/qV0wY9ecWmL7cUHlBRWxs=*Domainkey-signature*: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:content-type; b=ovdeZQHoLbToYkOhyYFaOjJcoFkffI2YcpgxihegzAmzREZv63jPIoXMbdFdgsjxDV MCR9YPVeqO5H5F1mieHcFRi9v7eZ394WPmvMIuA3jzac5MjQPnfCtwuXTeJ+R7Fm1Ymz dehLt7mCMjTRdzisEBM+vMsSAyKQav9gGa3+Q=

Hi, At the moment, our Geometry module makes the assumption that direct isometries have positive determinant, and indirect isometries have negative determinant. In the southern hemisphere it's the opposite --- this is the mathematical phenomenon behind the famous Coriolis effect which makes cyclones spin counter clockwise in the northern hemisphere, and clockwise in the southern hemisphere. http://en.wikipedia.org/wiki/Coriolis_effect http://en.wikipedia.org/wiki/Cyclone I'm working on a patch at the moment but I'm not sure how to best implement hemisphere detection. It could be selected at compile-time, but that means that binaries can only work in one hemisphere. Or we could implement runtime hemisphere detection on platforms that support it (more and more devices have accelerometers that detect very well the coriolis effect) or just use an internet-based service for geolocation, but i'm not sure if it's reasonable to let Eigen depend on a HTTP library? We could make that an optional dependency though. Cheers, Benoit

**Follow-Ups**:**Re: [eigen] southern hemisphere support in the Geometry module?***From:*Manuel Yguel

**Re: [eigen] southern hemisphere support in the Geometry module?***From:*Rohit Garg

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