scale issue

[Kanahiro]

• QGIS provide a scales in each projection.
• the scales are not correct in global scale in non-geodestic projection.
  • e.g.) scale in web-mercator means a scale on equater

[bordoray]

Investigation in progress : Scale factor = 1/cos(latitude)

refs:

• https://gis.stackexchange.com/questions/93332/calculating-distance-scale-factor-by-latitude-for-mercator
• https://en.wikipedia.org/wiki/Mercator_projection#Scale_factor

results on qgis depending on latitude:

calculated scale : 2994408.2013047514
Latitude: 25.855500599895247
Scale Factor: 1.1112385892564363

calculated scale : 2994408.2013047514
Latitude: 36.63425998848918
Scale Factor: 1.2461667610335012

calculated scale : 2994408.2013047514
Latitude: 45.63643828579945
Scale Factor: 1.4301879142998573

calculated scale : 2994408.2013047514
Latitude: 64.7501353833507
Scale Factor: 2.344299796305868

calculated scale : 2994408.2013047514
Latitude: 69.46402503064274
Scale Factor: 2.8506642625807803

[bordoray]

Note to myself if geographic test

QgsProject.instance().crs().isGeographic()

[bordoray]

Scale factor using PyQGIS

QgsProject.instance().crs().factors(QgsPoint(129.38109,28.29317)).parallelScale()
1.1348203411033124
QgsProject.instance().crs().factors(QgsPoint(129.38109,28.29317)).meridionalScale()
1.0044692066757388

QgsProject.instance().crs().factors(QgsPoint(141.8803,45.5082)).parallelScale()
1.4244934909888043
QgsProject.instance().crs().factors(QgsPoint(141.8803,45.5082)).meridionalScale()
1.0015995958532242

[bordoray]

Reminder https://mierune.slack.com/archives/C054M54KLSU/p1686027294170319