The 1/2 Pi Circle shawl shape is the one of the shawl shape recipe in Shawl Geometry Book One - a collection of basic shawl shape recipes that we all know and love.

More about Shawl Geometry Book One:
Starting from scratch every time you want to cast on a new shawl sucks.

But what if you had an easy to browse resource of shawl shapes?

A reference book of shawl shaping that laid out all the numbers, and all the calculations. Like a stitch dictionary, but for shapes instead of stitch patterns.

That’s what the Shawl Geometry Books are.

Shawl Geometry Book One lays out knitting recipes for the basic shawl shapes we all know and love.

This book contains 28 shawl shapes, with 54 knitting recipes, all laid out in clear, straight to the point knitting instructions, so that you can cast on right away.

The shapes available in Shawl Geometry Book One include:
Square Knit in the Round, Edge to Edge Square, Bias Square, Square with a Diagonal Slit, Mitered Square, plus Basic and Less Basic Rectangles, Right Triangle, Triangle with Wings, Side to Side Triangle, two Asymmetrical Side to Side Triangles, and the Shallower Triangle, all four ways to knit a circular shawl, the Octagon Circle, the Wedge Circle, the Hexagon Circle, and the Pi Circles, plus variations, Octagon Circle with a Slit, 3/4 Octagon Circle, 1/2 Octagon Circle, Wedge Circle with a Slit, 3/4 Wedge Circle, 1/2 Wedge Circle, Hexagon Circle with a Slit, 1/2 Hexagon Circle, and finally the Pi Circle with a Slit, 3/4 Pi Circle, 1/2 Pi Circle.
(for a visual, see the third photo)

For more information about Shawl Geometry Book One, and the other books in the series, see: http://www.hollychayes.com/shawl-geometry/