Tuesday 7 January 2014

Creating wee planets with GDAL

In my last blog post, we projected an equirectangular photograph on a sphere using three.js. Today, we'll use the same panorama to create a wee (miniature) planet.

A wee planet is a panorama projected to look like small planets using a stereographic projection. There is a great collection of wee planets from Alexandre Duret-Lutz on Flickr.

There are image software you can use to create wee planets, but why not be a real map nerd and use GDAL instead? We already have a 360°x180° panorama in an equirectangular projection. The only difference from a world map is that the panorama is not georeferenced. Let's do it with gdal_translate:

gdal_translate -of GTiff -a_ullr -180 90 180 -90 -a_srs EPSG:4326 bergsjostolen.jpg bergsjostolen.tif

We pretend our new GeoTIFF to be the world, and use gdalwarp to create a wee planet using the stereographic projection:

gdalwarp -wo SOURCE_EXTRA=10000 -r bilinear -te -22500000 -22500000 22500000 22500000 -ts 1000 1000 -s_srs EPSG:4326 -t_srs EPSG:3031 bergsjostolen.tif bergsjostolen-planet.tif

I'm using the Antarctic Polar Stereographic projection. If we use the same projection on a world map it will look like this:

I wanted the house on the top, and copied the projection string and changed the longitude rotation to -160:

gdalwarp -wo SOURCE_EXTRA=10000 -r bilinear -te -22500000 -22500000 22500000 22500000 -ts 1000 1000 -s_srs EPSG:4326 -t_srs "+proj=stere +lat_0=-90 +lat_ts=-71 +lon_0=-160 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs" bergsjostolen.tif bergsjostolen-planet.tif

There you go, a wee planet from a map nerd!

Snow kiters at Bergsjø.

Bergsjøstølen in the blue hour.

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