OpenStreetMap
From OpenAerialMap
OpenStreetMap (http://openstreetmap.org) is a project to create an editable map of the whole world, built largely from scratch, and released with an open content license. The maps (underlying data and rendered map images) are licensed CC-BY-SA-2.0
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OpenStreetMap mapping using aerial imagery
Most of OpenStreetMap mapping is based on GPS traces contributed by the community of mappers. People actually walk/cycle/drive down the streets recording tracks.
There is lots of potential to ease the mapping process, using aerial imagery. In fact they already do, because they have a special agreement with Yahoo! See their Yahoo! Aerial Imagery details. This is a great help, but it is limited in resolution, and (more importantly) limited in coverage. Only certain major cities are covered.
Using the OpenAerialMap WMS server
The OpenStreetMap editing application "JOSM" has the ability to load WMS layers via the WMS Plugin
The string to use for the WMS Plugin is:
Additionally, there is a TileCache serving tiles in the "spherical mercator" projection:
http://tile.openaerialmap.org/tiles/1.0.0/openaerialmap-900913/
You can use URLs like:
http://tile.openaerialmap.org/tiles/1.0.0/openaerialmap-900913/0/0/0.jpg
To access the TileCache: the x, y, z parameters match up to the Google Maps tile requests. This is somewhat like a TMS, but not quite.
License
The OpenStreetMap project is very sensitive to licensing issues. This is because the whole project is built on the premise that you are not allowed to create an open content map by any other means than by building it again from scratch. Picking a point from a google map, or even a google aerial image, is (as far the openstreetmap interpretation goes) deemed to be creating a 'derived work', which is not free of copyrights, so the same applies to any other source of aerial imagery (the license "rubs off", so it must be compatible)
As such the OAM project will not be of any use to openstreetmap, unless the OAM license is made clear, and license is compatible with the OpenStreetMap License. It would be a shame not to make OAM images available for this project to use.
The OpenStreetMap community has run into a lot of complex license discussions, which has led many to advocate a 'Go Public Domain' approach (to hell with licenses!) The OAM project should probably consider these discussions carefully, to get off on the right footing.
Attribution is a problem for OpenStreetMap. The map website is currently lacking any history display, but it does have 'source' tags in the data, which might provide some limited form of attribution (very hidden away, not exhaustively enforced, and potentially lost over time) This means OSM may not be able to use aerial imagery from here which has an attribution requirement. Generally this kind pain-in-the ass legal nit-picking problem does not reflect the spirit in which people release things with such licenses. However it is possible that organisation X who release a bunch of aerial photos on here, might expect to see their name appearing alongside any derived map images. In this case we cannot comply.
Some believe that this is only workable by dealing in public domain data (They also suggest OpenStreetMap releases to the Public Domain for the same kind of reasons) Others believe that problems like this can be smoothed over by clarifying license interpretation (see Discussion)
Orthorectification
Main article: Orthorectification
To do mapping using aerial imagery, you have to line up the images with the geolocations exactly. This involves, not just lining up the corners of a photo, but also correcting to account for lens distortions. The process is called orthorectification.
Orthorectification using OpenStreetMap data
OpenStreetMap maps/GPS coordinates could be useful as a resource for actually carrying out orthorectification. Note that this would mean the orthorectified OAM imagery might be regarded as a derived work of the OSM data!
- Links
- blog post on opengeodata.org - About the OAM project as relating to the OSM project
