Tackling Imagery Offsets - comprehensively

Dermot McNally, Dobini

Details about the talk:
OSM has, for a long time, made heavy use of aerial imagery for tracing. Traced map data frequently occurs in proximity to surveyed data, often mapped by users not familiar with the area. For this reason, misalignment of aerial imagery can and does negatively impact the map. The two most commonly used imagery sources, Yahoo and Bing, both have many areas of poorly aligned imagery, with errors sometimes as high as 20m.

Most commonly used editors have support for "simple" offset correction (alignment shifts along x and z axes). However, many mappers are unaware of this facility - indeed, many are unaware that imagery can be inaccurate in the first place - and those who are may not have a source of trusted surveyed data against which to calibrate.

I propose making time for presentation on this topic by interested parties. Ideally this would involve a short presentation of each proposed solution to the imagery offset problem. Those I know of are True Offset and Komzpa's work based on Ground Control Points. In addition, since OSM work to identify and correct errors has the potential to provide useful data to imagery providers, it would be ideal to include representatives from imagery donors (particularly Yahoo and Bing) to have their input. The panel discussion, if there is sufficient participation, would attempt to identify the best approach to ensuring accurate image alignment in editors and to find ways of removing obstacles (frequently legal) to the adoption of good solutions to the problem. The end goal is that all editors will display correctly aligned imagery in all cases and without any action on the part of users.

If a panel discussion is not possible or useful, I propose scaling back to a simple 20 minute talk on True Offset.

Details about the speaker:
Dermot McNally has spent most of his career in the area of Web Applications and Internet Technology generally. He is co-founder and former CTO of the online Tour Operator Directski.com. He has been mapping with OSM since 2007, mostly in Ireland, where he was responsible for much of the earliest backbone mapping (coastline, place name imports etc.). He has been a strong OSM evangelist within Ireland, mainly through presentations and mentoring new mappers. Together with Bartosz Fabianowski, Dermot designed and implemented the True Offset Process for automatic correction of aerial imagery errors.

Theme: map