.shp file, twice upload nodes places changes

[Allroads]

What steps will reproduce the problem?

1. When I open a .shp file with polygons in JOSM, I copy paste a polygon to the datalayer, set the OSM tags. And upload it to Openstreetmap.

2. The next day I go further, open this .shp file again, open a datalayer with osmdata from the database, then I see the nodes of the polygons does not match with the polygon of the .shp, so I can not copy paste the next polygon to the data layer, so that the nodes are exactly on the same place.

3. Then I run JOSM validation and fix the double nodes (this merges the polygon together).

I see that there is not a pattern that all nodes have the same deviation, I lays north than south, close further away, just random.

Any solution?

What is the expected result?

That the nodes lay on the same place.

What happens instead?

Second openining nodes lay moere random

Please provide any additional information below. Attach a screenshot if possible.

Repository Root: http://josm.openstreetmap.de/svn
Build-Date: 2015-02-01 02:33:54
Last Changed Author: Don-vip
Revision: 7995
Repository UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Relative URL: ^/trunk
URL: http://josm.openstreetmap.de/svn/trunk
Last Changed Date: 2015-01-31 15:17:59 +0100 (Sat, 31 Jan 2015)
Last Changed Rev: 7995

Identification: JOSM/1.5 (7995 en_GB) Windows 7 64-Bit
Memory Usage: 618 MB / 989 MB (88 MB allocated, but free)
Java version: 1.7.0_71, Oracle Corporation, Java HotSpot(TM) Client VM
Dataset consistency test: No problems found

[Allroads]

situation .shp visual, openstreetmap data less, yesterday copy

[stoecker]

Accuracy of OSM is not as high, as you expect. Values are rounded to 7(?) digits. Your offset seems to be in this range. Our real accuracy of data may be something like 10 meters, so mm or cm aren't really useful :-)

JOSM does not round it's own data (hmm, maybe when saving, don't know), but after server upload/download you will have rounded data.

[Allroads]

That is not good, now I can not go further with the import.

To much nearly double nodes.

This give not a quality map.

Is there a way to translate the .shp in front to osm rounded digits values? And saved this file osmroundedvalue.shp file to use it next time.

Or the opendata plugin does do that in front, maybe enchament, so we can use this file multiple times.

Numbers to be rounded are they always rounded the same way, so we get always the same result.

[stoecker]

It is always 7 digits after the comma. Don't know if rounded or simply truncated. You need to test yourself.

If you import the shape into an OSM file, save that with JOSM and run a small script (or an editor with regexp support) to reduce coordinates in the ASCII then you should have what you want. You could use this OSM file then as import base.