[OSM-newbies] Accuracy - GPS or LANDSAT

[Franc Carter]

Thanks,

I'll make a couple of more passes with the GPS and then look at aligning the
railway based on
that. It's not off by far, the probem is only that they cross on the map but
not in reality. They actually
run parallel for about 100m, which will make improving it easier.

cheers

On 5/1/07, David Groom <reviews at pacific-rim.net> wrote:
>
>
>
> ----- Original Message -----
> *From:* Franc Carter <franc.carter at gmail.com>
> *To:* newbies at openstreetmap.org
> *Sent:* Tuesday, May 01, 2007 1:53 PM
> *Subject:* [OSM-newbies] Accuracy - GPS or LANDSAT
>
>
> Hi,
>
> I have just started mapping the areas of Sydney Australia that I know (or
> at
> least travel through/to).
>
> I am using a GPS to get track logs and working from these, in one area my
> track log crosses a railway that is marked as 'source:landsat' and the
> road does
> not actually cross the track.
>
> So, I am wondering which is more likely to be accurate and how I should
> merge the
> two source to end up with a reasonably accurate result.
>
> Franc
>
> In the Southern UK the Landsat imagery is adrift by 10 - 20 meters.
>
> However I have also come across cases where two different GPS receivers
> give different results.
>
> I'd more likely trust the GPS, particularly if you have made a couple of
> passes down the same road and the results are consistent.
>
> Fortunately in JOSM its quite easy to move a whole way in one go, just
> select the move tool (keyboard shortcut M), move the mouse cursor to
> somewhere above the way which is not over a node, and then leftclick and
> drag and the whole way will move.
>
> You have tow options for aligning the railway.
>
> 1)  best guess as to where you think it is in comparison to the road you
> have mapped.
>
> 2) download the landsat imagery for the area, realign the landsat image to
> the known road, and then realign the railway to the position now shown by
> the Landsat
>
> David
>
>
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>
>


-- 
Franc
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