[OSM-talk] Combining OSM waterbody and elevation data for better map rendering and QA

Christoph Hormann chris_hormann at gmx.de
Thu Sep 12 12:59:31 UTC 2013


Hello,

I have completed a first version of a tool to modify elevation data by 
use of waterbody data from OSM (more precisely currently only the 
lakes, not the rivers).  Description of the process is on [1], the tool 
on [2].

Primary purpose is better display of lakes in 3d renderings but this can 
also be useful for relief rendering in 2d maps, i.e. avoiding contours 
intersecting lakes and for more accurate elevation profiles of routes.

The problem is of course that the processing takes some time (Europe at 
1 arc second resolution about a night) and changes in the waterbody 
data would require updates.

As a byproduct the process also puts out lists of possible errors in the 
waterbody data - places where the modification of the elevation model 
required is so large it cannot be correct.  From my first look these 
have a fairly good signal to noise ratio, i.e. the majority of them are 
actually errors in the OSM data (a large fraction are shadows in 
imagery that have been incorrectly interpreted as water like at [3] and 
[4]).  I put up a simple map to look at these for Europe on [5] but you 
can also find the point list on github.  In the long term this is not 
overly useful as a QA tool without frequent updates of course.

Greetings,

Christoph


[1] http://www.imagico.de/map/dem_water_en.php
[2] https://github.com/imagico/dem_water
[3] 
http://tools.geofabrik.de/mc/?lon=23.91222&lat=39.24613&zoom=13&num=2&mt0=mapnik&mt1=bing-satellite
[4] 
http://tools.geofabrik.de/mc/?lon=6.02164&lat=60.45423&zoom=13&num=2&mt0=mapnik&mt1=bing-satellite
[5] http://www.imagico.de/map/errormap_en.php

-- 
Christoph Hormann
http://www.imagico.de/



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