[OSM-newbies] Accuracy - GPS or LANDSAT

[David Groom]

  ----- Original Message ----- 
  From: Franc Carter 
  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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