Re: [udig-devel] missing prj files

[Adrian Custer <acuster@xxxxxxxxx>]

On Thu, 2008-06-05 at 14:41 +0200, Jesse Eichar wrote:
> 
> Here's a proposal for how things should operate when layers do not  
> have CRSs.  Let me know where you disagree:
> 
> 1.  Empty map.  Just show the data

We treat the coordinates as cartesian values: there is no geographic 3D
CRS and no projection.

> 2.  Add a prj-less layer to a map with all prj-less layers.  Just  
> display it all in the more or less cartesian projection.

Same as above.

> 3.  Add a prj-less layer to a map with the a SRS then the layer will  
> display if the coords are the same

same as what? as the output coordinate system? as any one of the input
layers? there will always be somewhere on the plane with identical
coordinates. So then you are talking about 'the same' being 'close in
value' but again the semantics are not obvious

> 4.  Add a referenced layer with the same srs to a map with all prj- 
> less layers then the map will ...
> 5.  Add a referenced layer with a different srs to a map with all prj- 
> less layers then the map will ...
> 
> 4 and 5 are slightly more difficult.  

What are they? same/different srs from what, from the display since all
the others don't have any? Again the semantics are not obvious.


It's a hard problem that requires some hard thinking to solve and I
doubt it can be made to 'just work' in any elegant way. 

One user friendly widget which is missing to tackle this is some kind of
'overview' canvas which shows schematically the relative location and
size of data sets. Often, when the viewer is willing to display
mis-matched data, one data layer will be way far away from the other and
occasionally be invisible for being much smaller than a pixel. The
overview dialog should therefore always show a data set as a block of a
minimum size, e.g. a 10x10 pixel. Of course, such a viewer needs to
operate in pure coordinate space and in any projected space used by the
renderer so it essentially requires its own renderer which makes the
widget very complex to construct.

Ah world, could you not re-invent yourself as a flat plate, say on top
of a stack of turtles?

cheers,
  adrian