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[mkgmap-dev] Contour lines with "Artefacts" near a vertical line situated at W0° 00' 00"

From Gerard CATTIAUX gerard-mkgmap at gmx.com on Thu Mar 10 13:15:31 GMT 2022



After many hours of time to get a correct knowledge of the most important
tools needed to produce Garmin map, like mkmap, Splitter.. and plenty of
hours to develop my own Styles files for mkgmap, I am now able to produce
local maps mainly for Fenix 6x or Garmin 66, specifically for Trail Running.

That help me also to have a mean to verify immediately all my contributions
to OSM database.


To have the best results for my personal maps, I use altitude data from



For flat part of the country, I generally generate contour lines with a 5m
space, in lieu of a 10m or 20m space between contours lines.

That choice seems for me a very good choice for as an example "Ile de
France" (Extended Region around Paris), where max altitude are between 150
to 200m.


I recently generate contourlines near La Rochelle in France for a local zone
called "Poitou-Charentes",


but unfortunately, I have artefacts, that I don't have for example in many
other regions of France.

These artefacts are also visible for 5m, 10m and 20m space between contours


These "artefacts" are described in the pdf files given at this link:



To generate my contour lines, I use mainly hgt2osm, with hgt files from

Hgt files in the example : 








Command line

hgt2osm -g HGT-AFAIRE --MinorDistance=10


Hgt2Osm, 13.11.2017, FSofT

64 Bit-OS: ja

Programmodus 64 Bit: ja

MinorDistance:           10

MediumFactor:            5

MajorFactor:             5

HGT-Verzeichnis:         HGT-AFAIRE


OutputOverwrite:         False

Höhenkorrektur:          -0.5

MinVerticePoints:        3

MinBoundingbox:          0.0005

Douglas-Peucker:         0.04

1. OSM-ID:               -1

mit OSMBound:            False

mit OSMBounds:           True

mit OSMTimestamp:        True

mit OSMVersion:          1

mit OSMVisible:          False

max. Punktanzahl je Weg: 500

mit 'contour_ext'-Tag:   True



At first sight, it seems that all these artefacts begin just near a vertical
line situated at W0° 00' 00" / E0° 00' 00" 


Any ideas to helps me to solve the problem?


Many thanks



Gerard Cattiaux


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