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tilezen / joerd

Joerd can be used to download, merge and generate tiles from digital elevation data
MIT License
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Elevation data gets affected by highrise buildings #169

Open nrdegroot opened 7 years ago

nrdegroot commented 7 years ago

In some highrise urban areas, notably in Asia as far as I noticed (Singapore, Manila, Bangkok), the elevation data seems to occasionally get affected by the highrise buildings in the area as bulges in the ground. Perhaps the highrise buildings get mistaken for actual elevation changes.

Example Suntec Tower 4 in Singapore: https://tile.mapzen.com/mapzen/terrain/v1/terrarium/15/25837/16266.png

In the tile image, you can see sharply defined green areas, which cause subtle depressions in the ground, because they correspond with the red channel dropping by one point on those areas. However you can also see a few more subtle, blurred green smudges with green values up to 120 (where the average around would only be 20), without the red channel changing, which cause quite a bulge when rendered according the the formula given in the documentation.

looking at Google street view for the area, it should be flat: https://www.google.com/maps/@1.2948357,103.8593009,3a,75y,255.86h,80.6t/data=!3m7!1e1!3m5!1s8gw3YOQ4AGIlTlhn99sW3A!2e0!6s%2F%2Fgeo0.ggpht.com%2Fcbk%3Fpanoid%3D8gw3YOQ4AGIlTlhn99sW3A%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D87.60546%26pitch%3D0%26thumbfov%3D100!7i13312!8i6656?hl=en

Additionally, some tiles have random spikes in the red channel, for example

https://tile.mapzen.com/mapzen/terrain/v1/terrarium/15/25836/16268.png

For almost all pixels, the red channel is either 127 or 128. However if you look at pixel coord 247,39; the red channel is suddenly 136, which causes a severe spike when rendered in 3D.

iandees commented 7 years ago

@nrdegroot in that area of the world, the highest resolution data is coming from SRTM, which is pretty noisy and doesn't look great above zoom 13. We're working on updating the terrain tiles now, but we haven't found any higher-resolution data for that area.

For example, here's the tile you're talking about in our current version of Terrain Tiles:

image

and here's the same tile as we have it currently in the upcoming tileset update:

image

nrdegroot commented 7 years ago

Thank you for the reply :)

The spikes can possibly be hidden with code, but the bulges are much harder to 'hide'.