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More conversion fun - Nick [entries|archive|friends|userinfo]
Nick

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More conversion fun [Jan. 18th, 2006|11:18 pm]
Nick
I've discovered that on the gps.gov.uk, if you register and sign in, you can download a funky excel spreadsheet. Into this you can plug locations in various formats, and it'll convert them into other formats for you.

Most importantly, it has an example of the WGS84 to OSGB36 transformation, and then on to easting and northing values.

Annoyingly, this spreadsheet doesn't fully work on the versions of Excel on all the boxes I can remote desktop into. Specifically, the WGS84 to OSGB36 is one of the bits that is broken :(

I have been able to view it in the excel viewer, but I am stuck with the sample values they've already entered into it. Using these, I can see I do now have the right calculation and input values (s converted from PPM, rx/ry/rz from arc seconds to radians etc). However, it looks like cumulative errors are the killer, because my calculated values slowly diverge from theirs the more steps I apply.

So, I think I'm going to have to figure out how to do double precision math in python, then convert to that. Afterwards, hopefully, my written (but not yet used) conversion stuff can be used in nmea_info.py. And then it'll be very handy :)

In other nmea_info.py news, I've spotted a bug in how I was formatting longitudes. So, I'll release v0.05 in a little bit, which'll fix this, and possibly also have a few minor tweaks to the logging of locations. More on that if I can get it to play nicely...
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Comments:
(Deleted comment)
From: gagravarr
2006-01-22 05:05 pm (UTC)
Wow, shame I didn't have that before, it's seriously useful!

Tracked down a missing bracket (doh!), so now it works :)
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