Using Marine Gravity Anomaly Map with Mapbox GL

Yesterday, a paper was published in Science on the creation of new, higher resolution maps of the ocean floor using gravity anomaly data collected via satellite. The authors write, “at scales smaller than 200 km, variations in marine gravity primarily reflect sea-floor topography.” Since rock has a different density than water, precise gravity measurements allow for an estimation of ocean depth. One of my first thoughts was to use this data in a map.

The authors provide their data for download; however, it is provided as GMT grid files, which are apparently common for oceanography research, instead of something more standard for GIS such as GeoTIFF. Using GMT, I was able to convert the data to the GDAL supported NetCDF format, although I had to reencode the file with CDO before GDAL would handle it. Using GDAL, I then reprojected the data in EPSG:3857, converted it from floating point to integer, and created a GeoTIFF file to be more friendly to web mapping applications.
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Nugacious

Finding random comparisons interesting and being disappointed with the limited and deterministic nature of Wolfram Alpha’s quantity comparisons, I created Nugacious to make random comparisons between physical quantities. Using a set of about 700,000 physical quantities extracted from DBpedia, an ontology created from Wikipedia infoboxes, an essentially limitless number of random comparisons are provided with links to their source Wikipedia pages for your reading pleasure. Try it today!

Nugacious

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Pannellum 2.0

Two years in the making, I finally released Pannellum 2.0, which is a near complete rewrite. The renderer was replaced with raw WebGL, and multiresolution panorama support was added, along with a fallback CSS 3D renderer. Other additions include support for JSON configuration files, hotspots, tours, compass headings, CORS, partial panoramas, and cubic panoramas. I also put together a website for the viewer, registering pannellum.org. Unfortunately, there is still a dearth of documentation—something I need to work on. The below example demonstrates the multiresolution, hotspot, compass heading, and tour functionality using panoramas of the George Peabody Library and a JSON configuration file.

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Canoeing the Park River Under Hartford

The Park River once flowed past the the Connecticut State Capitol’s gilded dome and was the centerpiece of its namesake, Bushnell Park, in downtown Hartford, but it is now mostly forgotten. After the floods of 1936 and 1938, it was decided that the river should be buried to prevent future flood damage. Under the direction of the United States Army Corps of Engineers, construction started in late 1940 to entomb the river in dual 20 foot by 30 foot concrete conduits from the Connecticut River to the Capitol, and finished in 1944. While this conduit worked well, it was decided that more of the river needed to be buried after the flood of 1955, and the Greater Hartford Flood Commission was established soon thereafter. During the construction of Interstate 84 during the 1960s, the State Highway Department built additional sections of conduit under the direction of the Flood Commission. The final sections of conduit, as well as an auxiliary tunnel to the Connecticut River, were built by the United States Army Corps of Engineers under the Park River Local Protection Project, which was authorized in 1968, with construction finishing in 1981. In total, almost four miles of river are buried, plus an additional two mile long auxiliary tunnel.

Original Conduit Excavation and Invert Construction (from Hartford Engineering Dept. Report) Continue reading

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Volume of West Hill Pond

Since I have a bathymetric map of West Hill Pond, I thought it might be interesting to calculate the volume of the pond. The formula for calculating the volume of the frustum of a pyramid is V = \frac{1}{3} h \left( A_1 + A_2 + \sqrt{A_1 A_2} \right) where h is the height of the frustum, A_1 is the base area of the top of the frustum, and A_2 is the base area of the bottom of the frustum.1 This formula can be used with bathymetric contours to approximate the volume of a water body.2 Applying the formula to the bathymetric map of West Hill Pond results in a calculated volume of 9.3 × 106 m3, or 2.5 billion gallons.

West Hill Pond WPA Bathymetry

Also available is the bathymetric contour shapefile used.


  1. Conical Frustum — from Wolfram MathWorld 

  2. Taube, Clarence M. 2000. Instructions for winter lake mapping. Chapter 12 in Schneider, James C. (ed.) 2000. Manual of fisheries survey methods II: with periodic updates. Michigan Department of Natural Resources, Fisheries Special Report 25, Ann Arbor. 

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