OpenStreetMap

Data Misalignment issues in Taiwan

Posted by srividya_c on 13 September 2016 in English (English)

Over the past few weeks, Mapbox Data Team has been reviewing the OpenStreetMap Data quality in Taiwan with respect to Satellite imagery. By running a comparison against Bing Imagery and available GPS traces like Strava Heat Map we were seeing a notable data offset of 15-20 meters with respect to GPS Traces.

Data offset

Some observations

  • City centers have varying offset which is not aligning to GPS Traces.

  • Some major highways running between cities are having huge offset.

  • Roads in mountain areas are not matching to Strava traces

  • Some motorway junctions don't match with the GPS Traces

tw6

Community Involvement

  • With respect to the offset and data realignment, there have been a few discussions from our side in Taiwan mailing list and Taiwan OSM group in Facebook and members of Taiwan community have expressed their support in fixing these alignment problems.

New Mapbox Satellite for Taiwan

Seeing these imagery offset issues, Mapbox Satellite is now rendered with fresh imagery for major cities in Taiwan.

image

  • New Mapbox Satellite imagery samples

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Mapbox and Strava aligning compared to Bing Imagery

  • Mapbox Satellite aligning with Strava in misaligned motorway junction

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These are the cities where new Mapbox Satellite imagery is rendered. With respect to data misalignment and improvement, we hope Mapbox Satellite imagery will now enhance mapping in Taiwan!

Comment from BushmanK on 13 September 2016 at 16:22

It doesn't seem like correct practice to use junctions as a reference because ramps located above the ground are usually shifted on satellite imagery due to parallax, caused by off-nadir view angle. Aligning images of ramps to tracks makes only those ramps positioned correctly - everything on the ground level gets proportionally shifted. Only ground-level features should be used for imagery alignment in case of off-nadir view angle.

I had an idea that Mapbox employees are a bit more professional in the aspects of imagery handling and basics of photogrammetry (actually, this is "Trigonometry 101" problem).

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Comment from PlaneMad on 14 September 2016 at 06:56

Good catch BushmanK.

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Comment from BushmanK on 17 September 2016 at 17:14

Using my "follow the error" principle of OSM Wiki improvement, I've added several notes to Using Imagery article.

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