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