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I want to map the objects in a small pedestrian area (say, 20x20 meters). I have a pretty precise survey done on paper, down to centimeters.

JOSM has a bar at the bottom which displays useful info when drawing polygons - angle to the last segment, current segment length... but the segment length's precision is only displayed in decimeters (e.g. it shows "5.6 meters" with a single digit after the decimal point). I'd like one more digit of precision to get centimeters. This would make my mapping quite simple.

Is there a way to change that in JOSM, or another tool I can use to map this?

asked 28 Sep '15, 03:29

Federico%20Mena%20Quintero's gravatar image

Federico Men...
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accept rate: 0%


You could use JOSM's measurement plugin, or hack JOSM source to let you zoom closer. But there wouldn't be much point to it:

  • The OSM database stores coordinates in a format that has a 1.7cm granularity depending on where you are on earth (longitude granularity does get finer near the poles). So you can't store anything more precise in OSM.
  • Plate tectonics cause movements of more than 1cm/year in most places of the world, so while you can map something with cm accuracy relative to itself, the absolute position (which is what OSM stores) would need to be updated every year.
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answered 28 Sep '15, 11:56

Vincent%20de%20Phily's gravatar image

Vincent de P... ♦
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accept rate: 19%

Thanks, I'll try the measurement plugin :)

I'm fine with 1.7 cm granularity. I'm pretty sure my little area lies completely within a tectonic plate; if it cracks in two during an earthquake, I'll have bigger problems.

(28 Sep '15, 17:43) Federico Men...

Frederico, you’re able to get any length by zooming and some arithmetic + - up to 0.04 m using JOSM, suitable for a building with the aid of the original building drawings or a survey locally. Since the measurement at 0.04 m is divided into 4 sections you got 0.01 m. The mode of your GPS is much lower for instance between 2.00 and 10.00 m, so don’t use the trick for open spaces like you’ve mentioned, as Vincent mentioned the accuracy of OSM is not that good.

(28 Sep '15, 23:17) Hendrikklaas
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question asked: 28 Sep '15, 03:29

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last updated: 28 Sep '15, 23:17

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