[OSM-dev] Cartagen Knitter >> TMS, GeoTiff, can be used with JOSM

andrzej zaborowski balrogg at gmail.com
Tue Aug 10 04:31:57 BST 2010

Hi Jeffrey,

On 10 August 2010 04:17, Jeffrey Warren <warren at mit.edu> wrote:
> yes, google maps is a reference design - the code accepts any TMS. I'm going
> to add a few public domain options (USGS National Map is good within the US,
> for example) and an arbitrary TMS/WMS input.

Thanks, that would be ideal.  I was using the Cartagen Knitter in
firefox today (I know webkit is recommended, but I couldn't be
bothered installing yet) and the OSM vector data is not loading for
me.  Some other issues I noticed in firefox were:

* no way in the UI to disable base layer once it's enabled
* key press events seem to propagate back to the browser even when
they were processed by javascript (I may try to pin it down myself as
it seems this won't require knowing ruby programming). This results in
the text search bar opening if your browser has that enabled, which
then captures any other further presses until you close text search
* the server side generated geotiff/jpg/tms is of much lower quality
than what you see in the browser, for example it seems the javascript
renderer has a very clever way to display the higher resolution images
on top while the exported bitmap just renders them in the upload
order.  The edges of pictures are distorted.  Some pictures or parts
of them don't appear (possibly due to too high resolution?)

I really like the application, just mentioning the issues to help
trace them.  I'll try to use it in a workshop this weekend.

Some other thoughts I had: The imagery I used was made some time ago
and was not particularly taken for the purpose of mapping, so the
viewing angle in many pictures starts at some 30 deg, and then goes
all the way to 90 deg (the horizon line).  In most cases I wanted to
just use the part of the picture where the angle was between ~30 and
~60 deg so I had to crop it before uploading, while this could be done
in the application.

> Though i do wonder if there's ownership precedent for derived
> orthorectification... makes sense, but how would, for example, Yahoo feel
> about it given that they've allowed tracing.

Yes, I'm sure Yahoo is okay.  Google may be okay too if you asked
actual lawyers but it's at least a (sort of) convention in OSM to not
use Google even for georeferencing.

> Some people put big red X's on the ground before taking aerial
> imagery, noting their coordinates for this purpose.

In some countries there are also grids of official geodesic reference
points, so if you spot one of them in your picture, you can look up
some very the exact coordinates for that point.


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