[OSM-dev] Sanity check please - ignore GPS-point duplicates in track data

michael_j at email.de michael_j at email.de
Thu Jun 14 23:30:57 BST 2007


Hi, 

last week I have uploaded to OSM many gpx-files generated by my GPS-receiver. After uploading I noticed, that my GPS-receiver had been in Sports mode instead of Navigation mode and thus took GPS-points maybe 20 times  more often. This resulted in huge GPX-files.

As a result now downloading the uploaded GPS-points with Josm of other than tiny areas  becomes impossible.I have seen areas with only few GPS-tracks taken, however containing about 1 GPS-point per 20 square meters of the displayed area. 

Today I downloaded the bounding box (8.284247155697123,51.675814750870174,8.344998008366737,51.727143022309406) which is about 20 km x 20 km = 40 000 000 square meter. Until now Josm had downloaded about 1.500 000 GPS-points corresponding (380-http pages) and is still not finished. 

Here is the URL:
http://www.openstreetmap.org/api/0.4/trackpoints?bbox=8.284247155697123,51.675814750870174,8.344998008366737,51.727143022309406&page=0

When now looking at this track data it appears that very many GPS-points are identical with their predecessor. As no time information is provided - their information content has zero value. 

If you look at the above link, for example the following node is repeated 546 times:
<trkpt lat="51.71124" lon="8.336345"/>

In order to reduce the download time and the amount of memory needed by JOSM, it seems to be appropriate to consider:
1. dropping following duplicate GPS-points during upload to the OSM database or
2. dropping those at the OSM database during download or
3. including the repeat  information as optional parameter into the GPS-point  during download:
   E.g.: <trkpt lat="51.71124" lon="8.336345"/ repeat="546"/>

Additionally in order to save memory JOSM should consider dropping any GPS-points that are identical to their predecessor already during download.

Michael






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