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

From Gerd Petermann gpetermann_muenchen at hotmail.com on Fri Mar 11 10:34:16 GMT 2022

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 fails?


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 Sonny.

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 lines.

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 Sonny.
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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