SLUG Mailing List Archives
Re: [SLUG] OT: Vector data on Sydney CBD
- To: Jon Biddell <jon@xxxxxxxxx>
- Subject: Re: [SLUG] OT: Vector data on Sydney CBD
- From: Jamie Honan <jhonan@xxxxxxxxxxxxxxxx>
- Date: Wed Nov 28 10:24:01 2001
- Cc: slug@xxxxxxxxxxx
- User-agent: Mutt/1.2.5i
> I've been trying to get updated data for my Garmin eMap GPS for the last 6 months, as the stuff that Garmin were able to get suffers from a data translation problem - if the data is in (for example) AUS1994 format, and they converted it to NMEA or GARMIN format for the GPS, it shows points as being up to 500 metres out.
> For example, taking a reading from Richmond railway station with a 5 metre resolution (and access to 8 satellites) should be fairly accurate, yet the map says that I am 435 metres away from the station.
> Same applies for my offivce in the CBD - a reading (handheld, from the roof with 6 satellites and 10metre resolution) tells me that I work in Cockle Bay.
> To get the same accuracy as, for example, the USA enjoys (wether it be mapping CDs, GPS data or... *gasp*... M$ Roadmap) would cost you thousands of dollars, as it's not "public domain" in this country, whereas almost every other country on this planet that uses this makes it available either free or for a VERY minimal fee.
Is it possible that this may be a projection, or datum point problem?
The earth is spherical-ish, and projecting this sphere onto
2D maps has all sorts of problems.