[udig-devel] Consistant GIS image files w/ geo-referencing

[Jody Garnett]

backspaces wrote:
> So question number one is: Is there a way for me to export and image of a
> GIS area in uDig and get a consistent image of it (same pixel size/area,
> same uDig GIS content (i.e. same exact scale and same position, upper left
> corner or some similar reference)?  The screen-grab approach seems pretty
> extream!  :)
>   
A perfectly reasonable request: Check out the community section; Jesse 
has a PNG and PDF export example working over there.
You should be able to modify the code to export a consistent image each 
time; if needed you can place a rectangle
on the map blackboard and export that region each time. You may need to 
create your own tool to define that rectangle (or perhaps a dialog
to enter in the bounds?).
> By now you must be thinking we're pretty weird, but wait .. there's more! 
> After we do a run of the ABM, we import it into Blender, a 3D modeling
> system, so that we can get much more visually compelling movies.  So this
> means the image above must not only be consistent in terms pixel placement
> and area and so on, it must be geo-registered in some way.   As I understand
> it, there is the notion of a "world file" in GIS which is a registration
> file accompanying an image saying what the geo-coordinate of the upper left
> corner is, and what the pixel size is in world coordinates (i.e. how many
> meters on a side a pixel is).
>   
Right right; what you describe is the next step for that PNG tool. You 
can have a look at the example data from the uDig tutorial
(it includes some of those world files you need). I think the world file 
is simply the bounds; an "prj" file describe the projection
the bounds (and hense the image) are in. To figure out the size of a 
pixel from this information you would need to do some math.
> I've tried making a layer of two markers that would be the desired extent,
> using the uDig zoom-to-layer feature, and entering the scale as a consistent
> value, but this does not appear to work.  I get inconsistent zooms and
> entering a scale changes whenever I enter it to a similar scale but not the
> same scale.  I realize its asking uDig a lot to be pixel-perfect!
>
> Whew!  So is there a way for me to achieve this sort of repeatable export of
> a map area with a given pixel height and width, and with the geo-coordinate
> information so that it can be imported into other programs in a standard
> way??  How would you try to do this?
>   
Are you a programmer? If not can we ask you to hire one for a couple 
days work :-)
> I bet this is the weirdest use of uDig yet!
> Owen 
>   
Sounds like a great deal of fun,
Jody