BOUWMEESTER & ASSOCIATES
Sun & Shadow Position
with Modeling Applications in
Collision and Crime Scene Reconstruction,
Urban Development, Site Planning and Building Design
|What We Do
specific results are generated by allowing input for the following:
location (by geographic co-ordinates)
factor known as the "equation of time"
between "watch" time (Standard, Daylight) and local solar time.
developed the computer model from the principles of astronomy and
geodesy, taking into account a number of key elements that are so often
missing in published sun charts.
Published sun charts tend to simplify the complex geometry involved in
calculating the sun's position relative to an observer on the
ground. Such charts do not account for an observer's actual
location based on site specific latitude and longitude. They
usually present sun azimuth and altitude figures based on an average
latitude for a general area, and on a longitude equivalent to the
standard meridian of the time zone within which the chart
applies. As a result, a correction of up to +/- 1/2-hour must
The average position of the sun is based on an average 24-hour
day. Since the velocity of the earth varies as it moves
through its elliptical orbit around the sun, the sun's actual
position (i.e. the position that determines shadow location) varies
from the average by up to sixteen minutes of time. This
variation is equivalent to as much as 4 degrees longitude - almost 450
kilometres - and, therefore, the correction factor known as the
"equation of time" should be taken into account. Our model
Ignoring the above factors alone can result in an 'error' of up to
about three quarters of an hour in sun position and shadow calculations.
Sun charts usually provide solar positions in hourly intervals only,
requiring interpolation for times other than those listed. It
should be noted that azimuth and altitude figures cannot be
interpolated linearly, making interpolation difficult and prone to
error. Sun charts also typically provide data for selected
dates only, making it difficult to accurately determine the sun's
position and to assess shadow impacts for dates not listed.
Our solar model takes into account all of the above so that the sun's
position relative to an observer can be precisely calculated for any
location, for any date, and for any
local time - historical, present and future. The model generates not
only the extent and position of shadows at any given point in time, but
it also calculates the duration of shadow impact -
a key indicator when assessing degree of impact.
Ralph Bouwmeester, P. Eng.
R. Bouwmeester & Associates
Barrie, Ontario Canada
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