Angle

As explained in D3.js in Action, Third Edition

An angle is the measure of rotation from a reference direction to a point or geometric ray.

An angle measures rotation from a reference direction to a geometric ray or point. In a polar coordinate system, it works with a radius to describe position around an origin. section 4.4.1

Use angles to position and construct arcs in SVG visualizations:

• Measure the angle clockwise from the 12 o’clock reference direction. section 4.4.1
• Convert a percentage into degrees by multiplying it by 360. section 4.4.1
• Convert degrees to radians by multiplying by π and dividing by 180, because D3’s arc generator expects radians. section 4.4.1 section 4.5
• Provide starting and ending angles to d3.arc(), alongside inner and outer radii, to define an arc. section 4.5

Mapping precipitation days to an arc

If 126 of 365 days contain precipitation, the percentage is about 35%. Convert that percentage to 126 degrees, then convert 126 degrees to radians before passing the value to an arc generator. section 4.4.1

Figure 4.24 The dimensions of a Cartesian coordinate system are perpendicular to one another, while the polar coordinate system uses the radius and angle dimensions to describe a position in space.

Compare Cartesian coordinates, which use perpendicular x and y dimensions, with polar coordinates, which use radius and angle. section 4.4.1

How D3.js in Action, Third Edition covers it

How deep it goes

Explains polar positioning, percentage-to-angle calculations, degree-to-radian conversion, and D3 arc accessors.

Examples

Uses a precipitation chart that maps 35 percent of 2021 days to a 126-degree arc.

What you can do after

Apply angles via D3’s arc generator to construct SVG arcs from percentages and radii.

How it connects

Connects angles with polar coordinates, Cartesian coordinates, SVG arcs, radians, and D3’s arc generator.

liveBookmanning.com

Read D3.js in Action, Third Edition on liveBook Get the book at manning.com

Also explained in

• 

  liveBookmanning.com
  Math for Web DesignAn angle is the geometric measure of the separation between two intersecting rays or sides.

Compare how 2 books explain angle →

Related concepts

• angle-based outlier detectionused by · Angle-based outlier detection is an outlier-detection algorithm that evaluates observations using the variation of angles formed with pairs of other observations, with distance playing a secondary role.
• degreesmeasures · A degree is a unit of angular measurement equal to one three-hundred-sixtieth of a full revolution.
• Math.atan2produced by · Math.atan2 is a two-argument inverse tangent function that returns the angle, typically in radians, of a point from its signed coordinates while distinguishing quadrants.
• cosine similaritymeasured by · Cosine similarity measures the directional alignment of two nonzero vectors as the cosine of the angle between them, equivalently their dot product divided by the product of their magnitudes.
• polar coordinatepart of · A polar coordinate specifies a point in two-dimensional space by its distance from an origin and its angle relative to a reference direction.
• radianmeasures · A radian is an angular unit defined by the angle at a circle’s center subtended by an arc whose length equals the circle’s radius.

This explainer was generated by Manning's knowledge graph from the text of D3.js in Action, Third Edition. The section links point to the parts of the book it draws on.