[OSM-newbies] new to OSM editing - advice on coping with gpx/ POTLATCH offset

[Andy Robinson (blackadder-lists)]

Thomas Meller wrote:
>Sent: 16 January 2009 6:02 PM
>To: newbies at openstreetmap.org
>Subject: Re: [OSM-newbies] new to OSM editing - advice on coping with gpx/
>POTLATCH offset
>
>Hello James,
>
>I tend to doing the least possible. GPS data are a bit tricky.
>If I find that a way's character is not what someone mapped I edit the OSM
>data or redo the whole way.
>That depends on how much work that might be.
>In Potlatch, it can be better to delete the way and do it from scratch.
>So an undelete is possible and I don't have to respect the other's effort.
>All in all, my own measurements can be wrong as well.
>
>Better have a look at other satelite fotos, your own experience or
>topographic maps and then judge by your confidence.

Just a point of note here. While is fine to be using the Yahoo! aerial
imagery for verification the same is not true of other commercial
satellite/aerial views where no agreement has been made between OSM and the
data provider. So steer away from looking at Google/Microsoft or any other
commercial offering as we don't want your data to be queried (and maybe
later removed) on the basis that you derived from someone else's information
without permission.

With respect to the Yahoo! imagery we know that its rectification accuracy
is pretty good most of the time but that it can be offset by a few metres.
I've seen imagery about a year ago which was clearly 30m off for instance.
The best option is to gather sufficient GPS data along the same paths so
that you feel comfortable about the shift and then either slide features
individually or select the lot with JOSM and move everything. Worth adding a
note to moved stuff so that others know the basis as to why.

Cheers

Andy


>
>-------- Original-Nachricht --------
>> Datum: Thu, 15 Jan 2009 00:47:53 +0000 (UTC)
>> Von: JW <jameswillmer at googlemail.com>
>> An: newbies at openstreetmap.org
>> Betreff: [OSM-newbies] new to OSM editing - advice on coping with gpx /
>	POTLATCH offset
>
>> Hi all
>>
>> I started small by adding some .gpx data
>> (Blackberry curve / bbtracker.org app)
>> to local maps in areas which i know well.
>> This area has been mapped
>> previously by someone using potlatch and the
>> yahoo available satellite photos (UK)
>>
>> It turns out that there seems to be an
>> offset between potlatch  locations and
>> .gpx data i record - maybe 5 to 10m or so.
>>
>>
>> There are a few courses of action
>>
>> 1) trust my phone gps .gpx data is correct
>> and change all potlatch locations as
>> i can..... this is not practical for
>> a small edit added to a large mapped area
>>
>> 2) don't worry about it this is
>> within normal gps errors ..... just "interpret"
>> where the footpath is and add it beside the potlatch road.
>>
>> 3) something else?
>>
>> What do others do?
>>
>> Ciao
>> JW
>>
>>
>> _______________________________________________
>> newbies mailing list
>> newbies at openstreetmap.org
>> http://lists.openstreetmap.org/listinfo/newbies
>
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