Relief maps
From OpenStreetMap
Relief maps would be tile images with each pixel colour-coded according to the ground height at that location.
Example images on:
Original email from the developer of those maps:
Contents |
Data source: SRTM
Home page at NASA, with data for the world, and higher resolution data for the USA.
file format (2 bytes per sample, given in unprojected tiles of 1201x1201 size)
Create or download
Existing tiles are available - do we want to host these (and interpolate for z10-z17) rather than creating our own?
Download link - about 500MB (only goes to zoom-level 9. levels 10 (2GB) & 11 (6GB) presumably available upon email request)
Colour coding
Discussion on colour scheme to use
- colorized by altitude (as seen in example on top right)
- shaded relief (levels of gray), just to indicate relative slopes, mountain ridges, not just absolute height... preferably transparent png, so it can alternatively also be put over landsat or some other background.
- combination of above (=shaded, colorized relief)
+
=
a proposal
Altitude-coded colour bands are more useful than shading or contours, giving information about (approximate) absolute elevation (which colour) and, more importantly, steepness of terrain (rate that colours change). A possible approach would be to colour bands at increasing (geometric as oppose to arithmetic) heights above sea level with the band width doubling for each band. This shows small but significant terrain changes at lower altitudes without the need for large numbers of bands in mountainous areas. The colour scheme here (easily implemented as an algorithm) uses greens for low altitudes shading through tan colours for hilly areas to greys for mountains, with all very high mountain areas in the >4095m shown white. (This should be discussed. Djam 10:53, 20 July 2008 (UTC))
Rather creating shape files for contours or bands, they could be processed as bitmap relief image tiles used as backgrounds to transparent tiles showing roads and other features. The elevations could be taken from the 3-arc-second SRTM data set and the relief tiles would only need to be produced once as (barring volcanoes and earthquakes) the terrain does not change rapidly. --Elvinibbotson 09:22, 20 March 2008 (UTC)
Elevation Contour Lines
See Srtm2Osm, eg:
See also wikipedia:Cartographic relief depiction.
Maps showing relief
- The cycle map and OpenPisteMap now show contour lines on slippy map tiles, re-rendered at regular intervals. Technical set-up is described on the Contours page.
- FreeMap ([1]) shows contour lines together with OSM data on a slippy map. Rendering code is available in SVN.
Existing software
- Srtm2Osm converts SRTM data to OSM xml, which can be rendered using Osmarender, Tiles@home and Kosmos
- Kosmos in itself has relief map capabilities (shading, elevation coloring). Future versions will include integrated contours generation tool and will extend the relief shading to the tiles generation.
TODO: what existing software is available to generate "google-format" image tiles from SRTM? How fast is it?
Interesting articles and examples
Other tasks
Allocate storage and server space for the tiles
Need to make the tiles@home map layer properly transparent, so that it can be overlaid (either over srtm relief or landsat or simple land/sea tiles).
Mapnik tiles aren't antialiased, so it's fairly trivial to remove the white background from existing tiles (though it would still be useful if they were naturally transparent)
