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

[Shaun McDonald]

On 14 Jun 2007, at 23:30, michael_j at email.de wrote:

> 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  
> (8.284247155697123,51.675814750870174,8.344998008366737,51.72714302230 
> 9406) 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=8.284247155697123,51.675814750870174,8.344998008366737,51.7271430 
> 22309406&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.

gpsbabel has a filtering option to drop duplicate points. From  
gpsbabel --help:
         duplicate             Remove Duplicates
           shortname             Suppress duplicate waypoints based  
on name
           location              Suppress duplicate waypoint based on  
coords
           all                   Suppress all instances of duplicates
           correct               Use coords from duplicate points

Thus you would use the option -x duplicate,all prior to the upload.  
Maybe we could do this as part of the upload process.

Shaun

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