[josm-dev] Proj4J - New plugin supporting 3000+ projections

[Josh Doe]

This plugin is now in SVN, and I have published the JAR so if you're
interested you should be able to install from within JOSM. Be sure to
test it before assuming it is correct! I tested it with several
projections that I'm interested in, and they all seemed to work fine,
but this plugin certainly has some issues. Please let me know if you
find any bugs either via Trac or email.

Frederik pointed out a number of potential issues when using arbitrary
projections, which apply not only to projections supported by this
plugin but any projection really. If you come across any issues or
bugs please let me know!

-Josh

On Fri, Feb 25, 2011 at 4:09 AM, Frederik Ramm <frederik at remote.org> wrote:
> Hi,
>
> On 02/25/2011 05:10 AM, Josh Doe wrote:
>>
>> Perhaps my sensationalist subject line turned people off from this.
>> Any chance this could get added to the svn? I'd like to submit patches
>> against that rather than continually updating the zip on the ticket.
>> I'd do so myself, but I don't want to be presumptuous and ask for an
>> svn account.
>
> Go ahead and request an OSM SVN account, it's nothing presumptuous.
>
> I see some trouble coming up when this plugin interacts with other stuff,
> like the tile/WMS backgrounds and the ImportImage or PDF plugins.
>
> These problems already exist - your plugin doesn't create them; it's just
> that your plugin opens the door to people using all kinds of strange
> projections and believing that was "supported".
>
> Problems I suspect may arise:
>
> * Selecting a projection that is only valid for a small part of the world
> (indeed, most of the "3000+" will not work for the whole planet) and then
> zooming out - what will happen? Do you actually include the validity
> bounding boxes for each and switch back to plain Mercator outside of that
> area?
>
> * Imagery subsystem (tile/WMS) is likely to, at best, squish or stretch
> images, but will not properly reproject them, which will lead to noticeable
> inaccuracies especially on low to medium zoomlevels. The kind of inaccuracy
> depends on the projection chosen. For example, if you set JOSM ot 4326 then
> request tiles from a Mercator tile server, the middle section of each tile
> will be displaced towards the equator. This effect is probably more
> pronounced with other source/destination combinations.
>
> * ImportImage plugin contains its own projection library which (a) may be
> partly unnecessary if your plugin is loaded - maybe ImportImage could be
> made to depend on yours? - and (b) it tries to reproject loaded images to
> the display projection, one should try if this really works with the usual
> projections.
>
> * Gauss-Krueger proejctions commonly used in Germany are not processed by
> proj.4 accurately unless an extra grid file (BETA2007.gsb) is used, see
> http://osgeo-org.1803224.n2.nabble.com/gdal-dev-Re-ogr2ogr-BeTA2007-grid-td4900463.html
> - will that be possible with your plugin?
>
> * I have no clue what the PDF import plugin does if your viewport is
> projected. I assume that there's a whole host of plugins assuming that you
> can just scale an image to the viewport and it will somehow magically work.
>
> Don't let these points discourage you from continuing your work, it is most
> appreciated. I would just advise some caution when saying that certain
> projections are now "supported" as this will naturally lead users to believe
> that "everything still works" if they select that projection - which may not
> always be the case :)
>
> Bye
> Frederik
>