Re: [udig-devel] CRS

[Jesse Eichar <jeichar@xxxxxxxxxxxxxxx>]

On Mon, 2005-04-18 at 19:57 -0400, dblasby@xxxxxxxxxxxxx wrote:
> The CRS handling is quite strange.
> 
> I've already reported that the WMS requests are not correct, so I tried
> to use shapefiles.
> 
> I keep getting "Layer Data out of Bounds" errors.  Once I start getting
> the error, it doesnt go away and my maps no longer render.
> 
This is not an error this is a warning.  It may only mean that you are
zoomed in or away from that layer's data.  The second case occurs when
one layer has a known CRS and another does not.  I'll discuss that at
the end of the email.

> If there's not a .prj file with your .shp then udig gets a bit huffy and
> occationally throws Null Pointer Exceptions (like if you try to do a
> layer->get summary).
> 
> I dont know how to fix this inside udig.
> 
> How is CRS support supposed to work in udig?
> 
> dave
> 

CRS support is difficult because of a number of reasons:

1.  There is no good way to determine what the valid area of a CRS is.
The API is there but the data is not.  So sometimes I am unable to make
intelligent requests.  For example I try to transform my current bbox
but the transformation doesn't work...  What do I do?  I don't know the
valid area so I can't clip my bbox.

2.  Take the following scenario.  I have 1 layer with a known CRS, say
lat-long(doesn't matter) and a second layer without a CRS. The map is in
a CRS, probably Lat-Long.  So the first layer can be rendered no
problem.  but the second usually can't unless it happens to also be in
Lat-Long (That is the assumption.)  In this case you'll usually get a
Layer not in bounds warning.  

2a.  You also often can't zoom to the layer because the valid bounds of
Lat-Long is known so the request is a maximum of -180,180,-90,90.

Suggestions are welcome.

Jesse