Dbus api for gta2 accelerometers

[Al Johnson]

On Tuesday 15 September 2009, Rask Ingemann Lambertsen wrote:
> On Mon, Sep 14, 2009 at 01:36:35PM +0100, Al Johnson wrote:
> > Out of interest why you want to know the position of the points,
>
>    For simulation purposes. Aerial photographs can be used too, of course,
> but it is quite time consuming to measure the distances that way. Curves
> are also an issue that I hope the GPS will do away with.

If you're lucky it'll be in openstreetmap already. I was surprised by the 
level of detail on some of the railways while using navit on holiday recently. 
Even if they're not there already the OSM tools should make it relatively easy 
to get positions in from aerial photos, and the data into a vector format.

> > and how do
> > you intend to distinguish them from a lateral track defect?
>
>    I don't know if it can be done automatically. The idea is to detect the
> common crossing as the wheels pass over it, and maybe you can tell from the
> accelerometer readings that only wheels on one side ran over something or
> perhaps the data show a particular signature from the common crossing that
> a lateral track defect doesn't have.

For simple crossings look for a lateral acceleration in one direction, 
followed by a damped rebound and overshoot, a short gap, then a lateral 
acceleration in the opposite direction with damped rebound and overshoot. You 
will probably see some peaks in vertical acceleration on the crossings too. If 
you're lucky lateral defects won't occur in pairs, and they may have more 
overshoot. 

Aim to sit close to the bogie centre near the end of the carriage as you will 
get about double the signal that you would in the middle of the carriage.