djbutler

license: gpl-3.0

djbutler

This example demonstrates how to remap a monochrome image using a custom color scale. You might use this technique as an alternative to a CSV- or JSON-based heatmap; binary images can store lots of data efficiently.

The source image is a global heightmap from the Shuttle Radar Topography Mission, released as part of NASA’s Blue Marble collection at 8km resolution. The topography data is stored in a simple black-and-white, 8-bit PNG. Darker values represent lower elevations, and lighter values represent higher elevations. Colors are read out of the image using the Canvas API.

Since there are eight bits per channel, elevation value

djbutler

[
[103,104,104,105,105,106,106,106,107,107,106,106,105,105,104,104,104,104,105,107,107,106,105,105,107,108,109,110,110,110,110,110,110,109,109,109,109,109,109,108,107,107,107,107,106,106,105,104,104,104,104,104,104,104,103,103,103,103,102,102,101,101,100,100,100,100,100,99,98,97,97,96,96,96,96,96,96,96,95,95,95,94,94,94,94,94,94],
[104,104,105,105,106,106,107,107,107,107,107,107,107,106,106,106,106,106,106,108,108,108,106,106,108,109,110,110,112,112,113,112,111,110,110,110,110,109,109,109,108,107,107,107,107,106,106,105,104,104,104,104,104,104,104,103,103,103,103,102,102,101,101,100,100,100,100,99,99,98,97,97,96,96,96,96,96,96,96,95,95,95,94,94,94,94,94],
[104,105,105,106,106,107,107,108,108,108,108,108,108,108,108,108,108,108,108,108,110,110,110,110,110,110,110,111,113,115,116,115,113,112,110,110,110,110,110,110,109,108,108,108,108,107,106,105,105,105,105,105,105,104,104,104,104,103,103,103,102,102,102,101,100,100,100,99,99,98,97,97,96,96,96,96,96,96,96,96,95,95,94,94,94,94,94],
[105,105,106,106,107,107,108,

djbutler

djbutler

Click in the open space to add a node, drag from one node to another to add an edge.
Ctrl-drag a node to move the graph layout.
Click a node or an edge to select it.

When a node is selected: R toggles reflexivity, Delete removes the node.
When an edge is selected: L(eft), R(ight), B(oth) change direction, Delete removes the edge.

To see this example as part of a larger project, check out Modal Logic Playground!

djbutler

The counties of Ohio, generated via the us-atlas and using the Ohio State Plane North projection, part of the State Plane Coordinate System.