is time consuming but easy. wouldn't do it by hand anymore, but if you feel the urge below is from googely...


Shadow length of trees, structures, or topographic features can be calculated based on the height of the element and the altitude angle of the sun at a given time of day during a given day of the year. Typically, longest shadows in winter, and shortest shadows in summer are used for solar access calculations in northern latitudes. Shadow length is calculated using the formula:

Height of the element


Shadow length = tan (altitude angle)


Example:

Latitude is 36 degrees

Noon Sun on December 21 = 30 degree altitude

Shadow for 40’ (12000 mm) tree

= 40 / 30°

= 69.28’ the length of the shadow

Get an old-school book on hand-draughting. It's too hard to explain without drawings. I'm sure one of Francis Ching's books will explain it well enough. There are at least two ways of doing it: the good-enough approximate method, and the technically correct method. Both take time. Even slower if you want to get actual sun angles involved, like jump is suggesting.

If you draw shadows manually to add a sense of depth to an elevation or plan it is common to use a 45º angle (also 30º and 60º). Length of the shadows can then be drawn at 2/3 the actual length or the full length. This simple approach works well on relatively planar elevations and plans. Work yourself through the planes of your elevation and you will get nice shadow detail around windows and eves as well as in areas of setbacks.

yeah, i second ching's books. particularly design drawing.

i agree with what everyone else has said.

you can also just underlay a copy of your plan offset the appropriate vertical and horizontal directions so you can just trace the outline of the shadow where the underlay's walls are located.

google descriptive geometry.

or sciagraphy...

use shadows to hide things you don't want clients to see...

umm which ching are you guys talking about?
Or any other titles~?

thanks alot by the way guys!!

The most accurate you'll get will be traced from a render, even a quick sketchup render will be pretty accurate.

You can measure shadows off a physical model if you have one of those charts where you move the desk lamp until the matchstick equals a particular length. You could probably get that on google somewhere. Can't recall the name of those now.

Oh and Design Drawing is the Ching you want. (as mentioned earlier)

There are lots of other books that will teach you the same thing more or less.

i personally like " Architectural Shades and Shadows" by Henry McGoodwin (1904) we referenced it in a studio i took that dealt with the design of a building that started with shadows and progress to a physical form.

google books link

there are some interesting articles in the beginning dealing with more than how to render shadows on architectural. how understanding shadows are important in ultimately understanding form and space. a good read.

we used a facsimile copy in the studio and it took me quite some time following graduation to track down. unfortunately it was not a first edition like i had hoped, but it was a 1922 printing and it included dated and graded shadow assignments from a student at the university of michigan in 1924 (he was a B student).

i second googling descriptive geometry.

I know how to calculate the length of the shadow, but could any one please tell me that how to calculate the angle of the shadow on the paper?

Thank You