[talk-au] Yahoo imagery in JOSM

Brent Easton b.easton at exemail.com.au
Sun Feb 17 05:47:09 GMT 2008


Are you aware that there are two different sets of Yahoo imagery of use to OSM? I call them the 1.6Km set and the 100m set because of the way you see them in JOSM. I guess you could call the Medium-res and Hi-res also. 

Sydney, Newcastle and some other urban areas are covered by the high-res set. You get the best quality when the scale slider on JOSM reads about 100m. At this scale, the native resolution of the imagery matches the resolution of JOSM.

The rest of regional NSW is covered by the the medium-res set. You get the best quality for these when the JOSM scale slider reads 1.6km. The pixelation in the Yahoo imagery you are seeing is when you download images at a scale >= 1.6Km and then zoom JOSM in. You cannot get better quality from those images by zooming in, they will automatically pixelate as JOSM trys to enlarge them.

In my experience, the High-res image set is usually very accurately aligned, the medium-res set varies, but is usually out. I find Landsat to be always out.


*********** REPLY SEPARATOR  ***********

On 17/02/2008 at 9:13 AM Liz  wrote:

>> I have compared Landsat and yahoo imagery in two different regions;
>> regional NSW and Sydney area.
>Two *large* images with landsat at the top and yahoo at the bottom; no 
>compression applied in conversion to jpeg, hence the size.
>www.billiau.net/~liz/osm/narra_lake.jpg (600KB)
>www.billiau.net/~liz/osm/lake_wyangan.jpg (460KB)
>they are very close to the same scale and therefore comparable
>viewed like this the landsat images are of consistent quality in these two 
>areas, not my original impression
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Brent Easton                       
University of Western Sydney                                   
Email: b.easton at uws.edu.au

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