Looking for a Web Tool to visualize Speed and Gradient on GPS Traces

I’m looking for a web tool that can show speed and gradient info directly on a GPS trace. I want to see if I can use that info to guess the mtb:scale or dirtbike:scale for unclassified trail segments and then later display those gradients in iD for further mapping.

Charts are nice and many apps have them, but having color-coded gradients right on the GPS trace would be better.

Screen Shot 2567-05-16 at 14.05.54

I’ve played around with gradients and Mapbox’s GEOJSON SimpleStyle before, so I might build it myself if needed. But first, I want to see if there’s something out there that already does this.

From things I have read in the past I think the vertical accuracy on GPS is generally poor enough that most applications that show an elevation profile actually “drop” the points onto a terrain model before plotting them.

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Good point. In the screenshot above, I have done exactly that using SRTM/HGT files based on lat/lon.

Freemaps.sk does gradient, but not speed:

[Their (beautiful) render is available only for central and southeast Europe, but elsewhere one can switch to Carto or aerials from the toolbar at the bottom]

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