[OSM-talk] Announcement: Availability of True Offset web service

Dermot McNally dermotm at gmail.com
Thu Feb 17 23:47:04 GMT 2011


Hi,

Many of you will have followed earlier discussions of the True Offset
process, intended to solve as simply as possible the problem of
imagery offsets by enabling editors to, by default, calibrate
background imagery based on offset data managed by mappers. In this
way, inexperienced mappers or people tracing without local knowledge
can avoid polluting the map with badly offset contributions.

The service is now live and seems to be working well on the dev server
and I have updated the wiki page to reflect this and some late
changes:

http://wiki.openstreetmap.org/wiki/True_Offset_Process

The highlights:

* You can try it at:
http://mackerski.dev.openstreetmap.org/offset/1.0/offset/bing/20/53.26/-6.67

* I have re-documented the meanings of the offset northing and easting
to ensure compatibility in units and sign with the offset bookmarks
already exposed by the JOSM Imagery module.

* This restatement of meaning may lead to a sign shift for one or
other of the values. So if you have previously entered offset data for
consumption by True Offset, please check that it is still correct.
This goes doubly for anybody who recorded offsets based on the
earliest proposals which used metres instead of degrees.

* Offset Database updates are currently manual (this will change). So
for now, if you add or change some offset data, please let me know so
I can cause it to take effect.

* Most of my test offset data has been for Bing imagery in Ireland.
Until the next database update, some of these may be inaccurate.

My appeal: If you are a developer of one of the OSM editors that
supports background imagery layers, PLEASE build support for True
Offset, and please have your editors either apply the corrections
silently by default or at the very least prompt users that a known
offset exists and offer to use it. While I hope True Offset is useful
to experienced mappers who already calibrate their imagery, its real
purpose is to avoid the destructive effect of tracing mappers who
don't even realise they can or should calibrate.

Happy Mapping!
Dermot

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