“Ghost Cars” on the I-35W Bridge
|| 8/3/2007 || 12:11 pm || 2 Comments Rendered || ||
When preparing the imagery for the previous map, I zoomed into the bridge and discovered that there are some “ghost cars” on the bridge.
There is really nothing supernatural about these cars, rather I believe they were created by one of two processes. The photographic artifacts were created by the cars driving at high speeds across the bridge when the photograph was taken. Or they could also be artifcats created by the blending of two different aerial photographs taken at different times. My best guess goes with the first, but I wouldn’t doubt if it were a combination of both. Regardless, they give the map a unique quaity that I wasn’t expecting. I am going to make a fractal version for tomorrow.
View a less pixellated view of the bridge:
A new change in Washington, DC’s imagery on Google’s servers
|| 7/10/2007 || 9:42 am || 2 Comments Rendered || ||
For the last 3 years I have followed how the aerial & satellite imagery of Washington, DC has been released, redacted, and remixed. This entry marks another important observation and a new discovery in Google Maps.
Last week I discovered the extent to which Google has updated their servers with the 2005 USGS aerial photography. My findings suggest that Google has censored much of downtown Washington, DC by not using a substanial amount of newer imagery.
over-projection after three derivatives
|| 4/19/2007 || 11:27 pm || Comments Off on over-projection after three derivatives || ||
I decided to compare the unmodified imagery of Oakland’s City Hall Plaza with the same location after 3 derivative maps (specifically a detail from Oakland Quilt #5). The result is quite interesting because it shows that the template I’ve been using for almost a year is not 100% perfect, which I knew already, but never cared to quantatively find out.
First there is too much light because the imagery on the right is slightly brighter. I did not compare the RGB histograms to see exactly how bright it is, but will check out in the future. Secondly, and more importantly, the template ever-so-slightly over-projects the imagery. The visual result is a slightly fuzzy version of the original, which, in most cases, does not matter because it’s ONLY noticable when shown at it’s full size. Once the map is reduced in size the fuzziness goes away.
To discover this I placed the original imagery on top of the used imagery and changed the opacity so that I could line up park on top each other and to match them I had to stretch the original imagery about .03%. Which after being used for 3 maps, this means my current template over-projects the imagery approximately .01%. This isn’t all the bad, but it means I need to do a slight resize to the template. Technically this means each map is 180 pixels too large, but honestly, I find that number a bit too high….
Comparative Meta-Data of the USGS Orthoimagery of Washington, DC – 2002 / 2005
|| 3/28/2007 || 9:50 am || Comments Off on Comparative Meta-Data of the USGS Orthoimagery of Washington, DC – 2002 / 2005 || ||
With the recent acquisition of the 2005 aerial photography of the White House, I decided to look over the computer generated meta-data that came bundled with the .tif file from the USGS. What I found was somewhat surprising in that the USGS makes note that “No metadata were received with this data.”
This essentially means that not only is the White House itself redacted, but the agency/corporation that took the pictures has been redacted as well. In the 2002 meta-data, it explicitly states the name of the corporation that was contracted to take the aerial photography, EarthData International of Maryland, LLC. Yet in the 2005 meta-data this information is suspiciously absent.
I must ask why? Was it done using government planes or was it contracted out? Moreover, why should this fact be removed from the meta-data?
To say the aerial photography magically arrived on the USGS servers is one thing, but to say that it was acquired by EarthData International of Maryland, LLC then processed at a USGS facility gives a better picture of the process involved in the creation of this imagery.
After the fold are the two meta-data files from the 2002 and 2005 USGS orthphotography. Of note is that there is more detailed information about the process invoved to create the 2005 orthoimagery, yet the source of it is withheld.
Daniel Denk at RemoteSensingTools has an interesting take on this issue.