YAMAKAGE

YAMAKAGE - Terrain-Aware Sunset and Sunrise Prediction ■Description Darkness falls earlier in the mountains than standard sunset times suggest. YAMAKAGE is a data field that reads surrounding terrain (elevation data) to calculate the "true sunrise and sunset times," taking actual mountains and shadows into account. ■Key Features ・Scans terrain data up to a 20 km radius from your current location. ・Compares the sun's trajectory with mountain elevations to predict exactly when the sun will be hidden (or appear). ・Ideal for trail running, mountaineering, road cycling in mountainous areas, and any activity requiring early light activation or careful schedule management. ■Displayed Data The following information is displayed. (Layout may vary depending on your device's screen size.) ・Countdown to the next update ・Next Sunrise time ・Next Sunset time ■How It Works To minimize battery consumption and processing load on your device, YAMAKAGE performs complex terrain calculations on a dedicated cloud server. ・The app sends your current coordinates to the dedicated server. ・The server reads publicly available global terrain data (terrain tile images) and instantly analyzes the elevation within a 20 km radius of your location. ・It combines the terrain cross-section with the sun's trajectory calculations to determine when the sun will hide behind (or emerge from) the mountains, and sends the results back to your device. ※Privacy Note: This app sends location data to an external server for sunset calculations, but it does not collect or transmit any personally identifiable information, such as account details or device identifiers. To maintain anonymity, it uses only a completely random, temporary hash value for communication. The transmitted location data is never stored (persisted) on the server; it is immediately discarded upon calculation completion (retained only temporarily as an operation log and is strictly unused for anything besides the calculation). Please use the app with peace of mind. ■Usage Notes (Please Read) ・Smartphone Connection Required: Because terrain data is fetched externally, your device must be connected via Bluetooth to your smartphone (Garmin Connect Mobile app) during your activity. ・Updates Every 5 Minutes: Due to the specifications of Garmin data fields, communication and terrain recalculations occur at a pace of "once every 5 minutes."Just after startup, it may show a "Connecting..." status for up to 5 minutes due to a waiting period. ・Exceptions: In regions experiencing midnight sun or polar night (e.g., Nordic countries in summer) where the concept of "sunrise/sunset" does not exist for the day, the time will be displayed as --:--. ・Communication Failure: If communication with the external server fails or the smartphone is disconnected, an "Update Failed" message will appear at the top. The app will attempt to communicate again in 5 minutes, and if successful, the display will return to normal. ■Margins of Error The times calculated by this app are estimates based on terrain data (approx. 38m mesh) and the sun's trajectory. Atmospheric conditions, the height of surrounding trees or buildings, and weather (clouds) are not taken into account, which may result in a margin of error ranging from a few minutes to over ten minutes compared to what you actually experience. Please do not over-rely on the assumption that "it will definitely be bright until the predicted time." Always plan your activities with an ample margin of safety. ■Watch App (Device App) https://apps.garmin.com/apps/48e48601-9506-4f67-b19c-59ca702c34b8 ■SourceCode https://github.com/tomopumipumi/yamakage ■Try it right in your browser! https://yamakage-site.pages.dev/