Magnetic declination is not considered for drawing the image arrows on photos

[rexendor@…]

What steps will reproduce the problem?

1. Load geotagged images with direction in the EXIF
2. Click on a photo and check the arrow drawn next to it.

What is the expected result?

The drawn arrow should point in the correct direction of the photo taken.

What happens instead?

The arrow direction is offseted depending of the geolocation and the date because the magnetic north is not the true/geographical north on the map. (​example offset map)

Please provide any additional information below. Attach a screenshot if possible.

The source file geoimage/GeoImageLayer.java:528 should add the magnetic declination in order to have a correct geographical direction.

For example OsmAnd ​adds the declination by getting it from android.hardware.GeomagneticField, which uses a downloaded model for the calulation (like ​https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml ).

JOSM should use a similar offline model or query the values from a public api based on the photo time and gps coordinates.

Relative:URL: ^/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2023-08-29 13:38:40 +0200 (Tue, 29 Aug 2023)
Revision:18822
Build-Date:2023-08-30 01:30:57
URL:https://josm.openstreetmap.de/svn/trunk

Identification: JOSM/1.5 (18822 en) Linux Debian GNU/Linux trixie/sid
Memory Usage: 334 MB / 4096 MB (179 MB allocated, but free)
Java version: 17.0.9-ea+6-Debian-1, Debian, OpenJDK 64-Bit Server VM
Look and Feel: javax.swing.plaf.metal.MetalLookAndFeel
Screen: :0.0 3840×2160 (scaling 1.00×1.00)
Maximum Screen Size: 3840×2160
Best cursor sizes: 16×16→16×16, 32×32→32×32
Environment variable LANG: en_US
System property file.encoding: UTF-8
System property sun.jnu.encoding: UTF-8
Locale info: en_US
Numbers with default locale: 1234567890 -> 1234567890
Desktop environment: XFCE
Java package: openjdk-17-jre:amd64-17.0.9~6ea-1
Java ATK Wrapper package: libatk-wrapper-java:all-0.38.0-1
libcommons-compress-java: libcommons-compress-java:all-1.22-1
libcommons-logging-java: libcommons-logging-java:all-1.2-2
fonts-noto: fonts-noto:all-20201225-1
VM arguments: [--module-path=/usr/share/openjfx/lib, --add-modules=java.scripting,java.sql,javafx.controls,javafx.media,javafx.swing,javafx.web, -Djosm.restart=true, -Djava.net.useSystemProxies=true, --add-exports=java.base/sun.security.action=ALL-UNNAMED, --add-exports=java.desktop/com.sun.imageio.plugins.jpeg=ALL-UNNAMED, --add-exports=java.desktop/com.sun.imageio.spi=ALL-UNNAMED]

Plugins:
+ FastDraw (36126)
+ HouseNumberTaggingTool (36178)
+ ImportImagePlugin (36184)
+ Mapillary (2.2.0)
+ PicLayer (1.0.3)
+ RoadSigns (36126)
+ apache-commons (36176)
+ apache-http (36176)
+ buildings_tools (36178)
+ ejml (36176)
+ geotools (36176)
+ imagery_offset_db (36126)
+ jackson (36176)
+ jaxb (36118)
+ jna (36176)
+ jts (36004)
+ log4j (36176)
+ measurement (36126)
+ photoadjust (36188)
+ reverter (36126)
+ tageditor (36126)
+ turnlanes-tagging (0.0.5)
+ turnrestrictions (36178)
+ undelete (36126)
+ utilsplugin2 (36178)

Tagging presets:
+ https://raw.githubusercontent.com/yopaseopor/traffic_signs_preset_JOSM/master/HU.zip

Map paint styles:
- https://josm.openstreetmap.de/josmfile?page=Styles/HU-HighlightHikingTrailSigns&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/LayerChecker&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Maxspeed&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Modified&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Enhanced_Lane_and_Road_Attributes&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Lane_features&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Lane_and_Road_Attributes&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/FixmeAndNote&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Coloured_Streets&zip=1
+ /tmp/elemstyles-bigfont.mapcss

Validator rules:
+ https://josm.openstreetmap.de/josmfile?page=Rules/OSMLint&zip=1

Last errors/warnings:
- 00004.679 E: Failed to locate image 'traffic_signs/HU/HU_C-031.png.png'
- 00004.680 W:  No overtaking: Could not get presets icon traffic_signs/HU/HU_C-031.png.png

[stoecker]

Why? The difference is not worth the effort for photo aligning. Which user takes photos with an direction accuracy that this starts to get a meaning? What's the use-case?

[anonymous]

Current phones store quite accurate directions and it is clearly visible that the arrow is systematically wrong - depending of course on the location you are. A lower effort solution could be to let the user add a fix offset angle to the geotagged images layer.

[taylor.smock]

In the US, the maximum declination is 14 degrees.
The max where people are likely to be is 26 degrees.

It might not be a bad idea to have an interface which a plugin could use to correct magnetic declination. Of course, someone has to either provide a patch or work on it.

@rexendor: If you really want that functionality, please provide a patch (see wiki:DevelopersGuide/PatchGuide). I have higher priority items to work on right now (example: #23286).

Things to note:

• We generally don't like adding additional libraries to JOSM core. Plugins can do whatever they want.