[Qgis-user] Australian GDA94 and UTM zones

[Ramon Andinach]

On 18/05/2011, at 19:30 , Matt Boyd wrote:

> Hi Group,
> I'm having some trouble getting my head around how to set up a project
> that covers multiple UTM zones. What projection do people use when
> they need to cover multiple zones? I also use some industry specific
> software and other users of that software are suggesting I use one UTM
> zone and force the zones either side to work in that crs. Given the
> issues I've had using data where people have done this sort of thing
> I'd like to avoid it and do it a right, or at least consistently wrong
> way.
> 
> Any ideas?
> Thanks
> Matt

If you're determined to use UTM, then the canonical kludge is the one that you've been given. You're right, its ugly but I'm guessing the industry specific software assumes a small(er) scale project and doesn't really get the zone thing. The kludge only works in a useful way, if your project is mostly in one zone, and only a little in the other - it does sound like you've got something that is in at least 3 zones and that's a big project. 

However, if[1] you're able to make sure that people document which UTM zone they're using, then you could have points_zoneA, points_zoneB, and points_zoneC and let QGIS do the on-the-fly thing.[2] But even then, if you decided to plot the entire project, I'd be expecting some serious distortion if they were plotted in UTM.

If I weren't able to break it down into subprojects that were more-or-less one zone, this is probably where I'd be seriously looking at a Lat/Long[3] recording system for a set of master co-ordinates. Then I had unconverted co-ordinates and could convert out when needed.

-ramon.

[1] is iff meaningful? This "if" is a big if, and only if it there is a practical way to make sure your field-workers will actually write the zone down.
[2] Note here that 1.7 can do on-the-fly to rasters too, so if you had a dev copy of that...
[3] such as GDA94 in the strict sense