[EMAIL PROTECTED] wrote on 02/07/2006 03:12:23 PM:
> Paul Ramsey ha scritto:
> > 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.
> Again, I believe this is a sensible approach. But in this case, allow
> the single layers to be reprojected (what happens
> when you add a layer in lat/long to a set of layers without CRS but in,
> say, UTM? You need a way to escape).
The extent of a Cartesian2D is likely to be (0,0) -> (m-1,n-1) for an m by
n scene with no georeferencing information. Likewise, each pixel is one
unit along the respective axes. I'm not sure how this could be considered
to fall within the range of Lat/Lon, unless you're talking about a scene
with less than 90 x 180 pixels, if your Lat/Lon units are degrees, or 1.57
by 3.14 pixels if your units are Radians.
It is quite correct to refuse to overlay an EngineeringCRS with
AnyOtherCRS. If the user wants to do so, a simple and viable means of
altering a CRS should be available (e.g., Arc/Info's define projection
thingy: can either select a predefined CRS, build one, or use the CRS
attached to some other layer.) The user needs to be in control of
assigning a projection like this: encountering an EngineeringCRS is
probably an indication that valid georeferencing info could not be
determined from the source in the "normal" way.
Put another way: GT and all software which builds on GT _cannot_ assume
that there is *always* a translation between the Source and Target CRS.
Insisting that the user resolve actual problems is a much more reasonable
approach than ArcMap's ("I see no problem here"). You can let the user
click on "assume the Grid's projection matches", but you should _force_
them to approve of the action you take. :)
Bryce
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