We have discussed this in the past, and would not be surprised if
there is something written down somewhere, if only in Jesse's notes.
This is just one of those things which has several cases, so instead
of spending effort on doing it right, we did the simple thing and use
WGS84 all the time.
- Use the CRS of the first layer added, and stick with that.
- If the first layer does not have a CRS, then we have to "guess" and,
- If the extents fall in the lat/lon range, it is probably lat/
lon, so use that
- If not use something generic, like CARTESIAN_2D
Which leads to the next set of cases, given a map in CARTESIAN_2D,
what to do when layers that have valid CRS information are added.
Probably ignore the CRS information and just draw them directly in.
The above is probably an amount of work to make operable, given the
conditional nature of so much of it. But it's probably the right
thing. Andrea have opinion?
P.
On Feb 7, 2006, at 10:45 AM, Jody Garnett wrote:
It really comes down to a numbers game, just like with fetures of
an unknown projection. Treating them as CRS.CARTESIAN_2D is
correct, but often as not people expect lat/long. We try and make
the most common thing the default. Right up there on our guidelines
"Use sensible defaults" is a uDig mantra.
The question is really what is sensible In this case? I do like the
sound of CARTESIAN_2D using the identiy transform and going
quickly. I am just not sure what the majority of these non
projected files are actually intended to be in.
A couple options:
- preference, with the default being lat/long.
- check the world file, and if it falls in the 180/-180 -90/+90
range use WGS84, and if not use CARTESIAN_2D. I figure that would
be the preference option "Guess".
- use the projection of the last thing loaded
We should also support an opperatoin to set the projection on both
shapefiles and world+image files.
Jody
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