Landsat 8 images are now freely available, including the 15-meter panchromatic band that was new in the Landsat 7 ETM+ sensor. The thermal bands have lower resolution than in the L7 sensor, but whatevs.
An immediate problem is how to deal with the images in the Level 1
Data Product. They're 16-bit TIFFs with dozens to hundreds of
megapixels; it turns out that, at least on my netbook, things like
ImageMagick (display and convert -sample anyway) and the GIMP just
do not manage to open them in a reasonable amount of RAM. netpbm
seems to be able to come through here, successfully generating a
thumbnail of a 225-megapixel image in only three minutes:
anytopnm LC82250842013110LGN01_B8.TIF | pnmscale -height=600 | \
pnmtopng > small-pan.png
The results in a rather dim, but still 16-bit, image, with a maximum
pixel value of 9007; a contrast autostretch with pgmnorm helps, but
leaves the image proper rather low in contrast, because the black
border pixels are so far from the image values. pnmhisteq results
in a striking and highly legible grayscale.
In the thumbnail, Buenos Aires is 40x34+365+278 out of the 624x600
image (found with display small-pan.png, then Image Edit → Region of
Interest). The original image is 15201x14621, according to anytopnm
LC82250842013110LGN01_B8.TIF | head -2. That means I should be able
to extract a 974x829 image at (8892, 6774) to find the city, using
pamcut:
time anytopnm LC82250842013110LGN01_B8.TIF | \
pamcut -left 8892 -top 6774 -width 974 -height 829 | \
pnmtopng > buenos-aires.png && \
< buenos-aires.png anytopnm | \
pnmhisteq | \
pnmtopng > buenos-aires-stretched.png
It would be a lot more efficient to break these images up into
compressed tiles of near the latency-bandwidth product of the disk
drive, using pamdice, and mipmap them, rather than spending over a
minute rereading the entire 400-megabyte GeoTIFF for every operation,
but at least it's workable. The above took a little under 90 seconds,
producing a striking image of most of the city (my RoI was a little
too conservative) in buenos-aires-stretched.png. Every street and
every plaza is clearly visible, but not every building. Using
pgmnorm instead of pnmhisteq gives much better results, with
large-scale patterns becoming visible. The resulting city map is only
about 1.5MB in PNG form or 470kB in JPEG form.
It would probably be a big improvement to add chroma data from the other bands, but that's a little more work.
Now that it's so easy to get unlimited Landsat 8 scenes, we can quite reasonably make movies of construction and the like, albeit on a block-by-block basis rather than a building-by-building basis. That is, you'll be able to see which block construction is happening on, but not what shape the buildings are, unless they're humongous.
(If we figure the latency-bandwidth product is 500kB and that we need about 1.5 bytes per pixel, the tile size would be around 600×600; this particular scene would then be 25×26 tiles, and it would probably make sense to produce 3:1, 9:1, and 27:1 reductions, adding another 1+9+27=37 reduced-size tiles to the original 650; the total would be some 350MB. Divide by roughly two to account for the fact that the zero pixels added around the edges compress to almost nothing.)
Extracting bands 1, 2, and 3 for red, green, and blue, we have
for band in 1 2 3; do
time anytopnm "LC82250842013110LGN01_B$band.TIF" |
pamcut -left 4446 -top 3387 -width 487 -height 415 |
pnmtopng > buenos-aires-$band.png
done
rgb3toppm <(anytopnm buenos-aires-3.png | pgmnorm) \
<(anytopnm buenos-aires-2.png | pgmnorm) \
<(anytopnm buenos-aires-1.png | pgmnorm) |
pnmtopng > buenos-aires.rgb.png
This produces a somewhat legible color image of the same region as previously, but it's fairly unsaturated.