Manual Raster Manipulation or, How Making Sh*t Up is Good Actually

The Problem:

This is Whalers Cove at Point Lobos courtesy of Bing Virtual Earth

Where it starts

Kelpfly in action. I really wish I got to be involved in this process.
From Sport Diver
Hillshade of raw CSUMB Seafloor Lab data
Seafloor composite made of terrestrial LiDAR data from USGS and bathymetry data from GEBCO and CSUMB

Where it gets hard

I started brushing on the right and you can see the artifact ridge as a lighter line with a sharp contrast there on the left side of the image.
Composite with mask cut from Bing Imagery

Brief Thematic Aside

Tharp with several maps she helped to create
Resampled composite with manually adjusted elevation. I wonder how long it would take to discover the Mid Ocean Rift the principle communication across the ocean were north and south instead of east and west.
Marie Tharp and Bruce Heezen made maps like this that were illustrated by Heinrich Berann

Making Sh*t Up for Art and Science

The completed image, available for purchase here.

More Detailed How-to: Satellite imagery mask

  1. Open up a basemap imagery layer (in my case I used Bing) and zoom in to the region of interest. Export the image as a geotiff using the Export Image function under the file menu. This is basically a georeferenced screengrab.
  2. Then, open up your newly saved file as a raster and add it to your canvas. You can turn off your basemap and see your georeferenced image locked into the right area of the planet due to the location data saved into the geotiff file.
  3. Because we are going to modify the image, we need to separate the geotiff file into a .WLD and a .TIFF so use Extract Projection in the Raster menu and save it with the .WLD.
  4. Now we can open the .TIFF in our favorite image manipulation software. I tried a couple of different approaches. First I used a lasso tool in GIMP to create a simple cutout like clipart from a magazine. Because the very shallow water at the beach is transparent, it was kind of hard to decide sometimes where to draw the line between land and water so I tried another one with Inkscape. There I used a bezier curve to create a mask polygon with solid fill and no outline and an edge blur of about 20%
  5. No matter how you modify the image, you can export it as a TIFF to a new folder. Then just drop in the .WLD from the initial export and modify the file names so they all match.
  6. Now you can add your mask to the QGIS canvas.

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Maps, conservation, insects, film, boats, scuba diving

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Andrew Middleton

Andrew Middleton

Maps, conservation, insects, film, boats, scuba diving

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