Re: [udig-devel] Projection WGS 84 as default

[Adrian Custer <acuster@xxxxxxxxx>]

Jody, jody, jody...

Do we both understand this totally? Is the message below completely
redundant? I hope so, but in case there is *any* confusion left, here
goes the pedantic rehash:

On Fri, 2007-11-09 at 01:37 +0200, Jody Garnett wrote:
> Right; well here is what I am thinking. When I go into a GIS shop most 
> times they just have directories full of shapefiles. No projections. The 
> files are all in the same projection and everybody knows that and they 
> don't bother to tell the tools (because that would be an extra step). 
> uDig is one of the few tools that cares; how should we work with these 
> shops that don't care?

(1) let's help them; the theme to my earlier message 

(2) they may be shops using 'GIS' but they sure aren't GIS shops---they
aren't being serious. But this stuff requires being totally rigorous
which may be hard the first time around, so (1) let's help them.

> 
> I figure we have 30 mins of their time (usually 10 mins) and if this is 
> slowing us down during that initial evaluation window then we need to do 
> something about it. Another idea would be to prompt the first time a 
> "unprojected" shp is loaded, 

YES. uDig should deal with the missing CRS/prj info, once at the 'add to
catalog' stage where we need to catch the missing CRS, and again at the
'add as map layer' stage where we need to warn about the missing
projection. uDig should catch those and then be friendly by giving users
a way to resolve the missing CRS or the missing projection. 

This requires:

        a) a split of the CRS and projection info/'open dialog' button
        in the map editor. These should be separate buttons since I may
        want to look at the different projections while keeping the CRS
        the same. e.g. GPS data has a perfectly valid CRS but no
        projection and a user may want to see it as 'unprojected',
        'mercator' ...
        
        b) a dialog to catch users adding resources with no CRS to the
        catalog. This would help users select or build a CRS. If users
        don't know, then we build a cartesian CRS (but be aware we may
        need to change this CRS by flipping axes once users see their
        data). Also note this is almost certainly WRONG, i.e. not what
        they really want, but it's the only 'default' we can possibly
        have. So perhaps we don't write this CRS out but merely keep it
        in memory as a virtual  'default'.
        
        c) a dialog to catch users adding a resource with no projection
        information to an empty map. By default we fall back on a
        cartesian projection (i.e. 'unprojected'). Actually, this could
        be a simple warning with all the functionality built into the
        'projection' button from (1).

{You get that right? You can have coordinates in long/lat that have a
perfectly valid CRS, but that CRS is without any projection info, e.g.
GPS data. To display them, uDig needs to pick a projection:
'unprojected' i.e. straight to screen x/y; 'mercator'; UTM ... So even
if the shapefile has a .prj file we are not out of the woods. (Actually,
maybe that's wrong; maybe shapefile .prj always have the desired
projection. Does the .prj of a GPS file actually always have a
projection?)}
        

> and show them the default, 

There is *no* default. There can be *no* default. If it were possible to
have defaults we would have solved this issue in 1970. EPSG:42xx can be
the current (incorrect) 'default' because it doesn't do anything---it
has no projection, so it merely dumps the x/y coordinates to the screen,
i.e. it is 'unprojected.' The only possible 'default' is:
        a) CRS is cartesian
        b) projection is 'unprojected'
        c) no override 'lat before long' 
so we dump the x/y coordinates of the resource directly to the screen
x/y. We should be able to let users flip their x and y although I'm not
sure how/where we could do that and where to store that setting. If
users have digitized a map then this straight 'unprojected' dump is
'correct' in that it's keeping the projection of the original, whatever
it may be.

The best way I can treat your words is: "How do we handle users that
have lots of data with no CRS/projection information and don't want us
to touch their files by adding any." Again, if they don't give us any
extra information the only thing we can do is to dump their coordinates
directly, unchanged to screen at most flipping the axes. So we 'default'
to treating their data as cartesian, with no projection, with long
before lat. (cont...)


> and have a 
> little check box that says "don't ask me again".
> 
> So it is my turn; this seems simply normal.
> 
> I think my idea about remembering a CRS per directory "path" may be the 
> best... it would catch the case where all the files in a directory are 
> in the same CRS; and we could prompt the user when they start working in 
> another directory.

(cont) If users want to give us a 'setting', then this could,
eventually, be kept and stored per 'service'. Indeed I'm going to want
to do something like that with the NASA blue marble data since it's off
in the highlands of Ethiopia so I want to be able to add a skewCRS to
that service so all the data comming off that server gets slid over into
the right place.

But this solution is for tomorrow. It is going to require us to start
tracking 'metainfo' about the resource, i.e. metadata that only we know
about that resource. So we can't really start playing this game until
(1) we clean up the catalog and (2) we start doing having a registry for
our 'metainfo'. 

With that, I'm going back to the storage API's.

--adrian



> Jody
> 
> 
> Adrian Custer wrote:
> > Maybe I'm dense but this seems simply wrong. You want to define the
> > values of the coordinates when they have no values? This sounds like I
> > give you a graph with the axes unlabeled and then you are going to
> > decide what the axes are. If we have no unit information we can only
> > plot this as x and y. 
> >
> > We could start guessing based on the size of the values but I don't
> > think that's what you are talking about. 
> >
> > Regardless, only the user can really start assigning 'default' CRS's;
> > uDig can only help to the extent of informing the user some key stuff is
> > missing and providing easy ways to fix missing info.
> >
> > --adrian
> >   
> 
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