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Show HN: GPX replay map that shows terrain shadows during activities (shademap.app)
42 points by tppiotrowski 2 days ago | hide | past | favorite | 14 comments

I've always had a hard time visualising the passage of time when viewing my GPX tracks. I wanted a better way to relive the moment and stimulate memories of what the day was like, so I put together this little visualisation that works with any .gpx track[1].

[1] .gpx track must have timestamps

If you don't have a .gpx track, you can also explore a world wide interactive map displaying terrain shadows throughout the year: https://shademap.app

Huh, I didn't realize that a summer sun in the northern hemisphere rises from ENE. https://www.suncalc.org/#/43.7434,-110.7355,12/2021.07.17/12...

Incorporating some of the overall sky colors might be neat, so that twilight looks different than midnight.

There was a recent discussion about this on HN: https://news.ycombinator.com/item?id=28420835

Make sure to draw the slider far enough to see the effect. The map has a grey overlay (time is before sunrise?) for the first 10% or so of the track.

Good suggestion. I need to improve the UX. And you are correct, the grey overlay is night time.

Really neat project.

Relevant to the parent suggestion, you might add some indicators on the slider to show where daytime is.

Where do you get the terrain elevation data? What resolution is it? I've been looking for good elevation data for another project.

Nextzen has freely available DEM tile data to zoom level 15, so about 5 meters/pixel. You need a free API key [1]

Mapbox has paid DEM data to zoom level 20, but I think it's just zoom level 15 scaled up (but the data is cleaner and more recent) [2]

Nextzen also open-sourced their elevation tile generator, but I haven't tried to generate my own tiles [3]

[1] https://www.nextzen.org/#terrain-tiles

[2] https://docs.mapbox.com/help/troubleshooting/access-elevatio...

[3] https://github.com/tilezen/joerd

This would be really interesting as a planning tool. Have you thought about making the start time selectable?

GPX replay is a proof-of-concept built on an API and map plugins I've been developing over the past year.

If you're interested, there are more features like the ability to view shade for any time/date/location throughout the year, search, building shadows, and high DPI mode available at the base url: https://shademap.app

I was waiting for it to animate. Maybe a play button would be nice. Real cool though.

Thank you. Autoplay would be amazing to prevent bounces from users that don't immediately know what the slider does but I'm a bit worried I will tax the GPU on low-end devices or large screens and end up freezing the page. Before I can introduce a play button I need to understand how to profile GPU performance and change the quality to maintain a healthy frame rate.

Maybe only add it to your demofiles?

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