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

From gerard-mkgmap at gmx.com gerard-mkgmap at gmx.com on Sat Mar 12 11:40:35 GMT 2022

Hi Gerd and Bernhard,

I made a lot of complementary tests that are still in progress to try to
understand the issue. 
Among these tests, the main results are: 

1)  Just after the conversion of one elementary tile (ex: N45W001.HGT ) with
hgt2osm, I can see the artefacts when I edit "mycontour.osm.pbf"  with JOSM.

2) I generate contour lines for a large surface comprising Benelux and
France, except a vertical band around 0%  (see:
NB: I use Data from SONNY
https://data.europa.eu/data/datasets/dtm-europe?locale=en), because they are
for me the best data for Europe, data are from 2021 and comprising LIDAR
--> The result after: All the contour lines are perfect. I don't see any
problem !!

3) I generate contour lines for the vertical band around 0° In France and a
local zone in SPAIN 
--> The Result: All contourlines have the Artefact at 0°

4) I choose also to generate contourlines from an another source of DEM data
for France around 0° (ALOS data from Japan Aerospace
--> The Result : Contourlines have all the same artefacts, just after
conversion with hgt2osm.

It is very clear for me, that SPLITTER and MKGMAP do  perfectly their jobs. 

For now, I will try to have a look on using  osm2srtm, but I am not sure
that it is possible to have the choice to use the recent data from SONNY as
input files !!

Best regards,


-----Message d'origine-----
De : mkgmap-dev [mailto:mkgmap-dev-bounces at lists.mkgmap.org.uk] De la part
de Gerd Petermann
Envoyé : vendredi 11 mars 2022 11:34
À : Development list for mkgmap
Objet : Re: [mkgmap-dev] Contour lines with "Artefacts" near a vertical line
situated at W0° 00' 00"

Hi Gerard,

I don't know the program hgt2osm, I would suggest to contact the author or
try one of the alternatives like srtm2osm or Phyghtmap:

Or do you think that the generated OSM data is okay and it is mkgmap that


Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von
Gerard CATTIAUX <gerard-mkgmap at gmx.com>
Gesendet: Donnerstag, 10. März 2022 14:15
An: mkgmap-dev at lists.mkgmap.org.uk
Betreff: [mkgmap-dev]  Contour lines with "Artefacts" near a vertical line
situated at W0° 00' 00"


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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