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:
https://wiki.openstreetmap.org/wiki/Srtm2Osm
https://wiki.openstreetmap.org/wiki/Phyghtmap

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

Gerd

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

Hello,

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 Sonny.
https://data.europa.eu/data/datasets/dtm-europe?locale=en

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",
http://download.geofabrik.de/europe/france/poitou-charentes.html
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 
lines.

These "artefacts" are described in the pdf files given at this link:
https://drive.google.com/file/d/1uiA51R4Kd_WYsdeTrEtevu2jJ_8aPinH/view?usp=sharing

To generate my contour lines, I use mainly hgt2osm, with hgt files from Sonny.
Hgt files in the example :
N46W002.zip
N46W001.zip
N46E000.zip
N45W002.zip
N45W001.zip
N45E000.zip

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
Mergefile:
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

Regards
Gerard Cattiaux

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