Introduction — SketchUp's Virtual Heliodon

SketchUp’s Geolocation and Shadow tools work together to create an accurate portrayal of real world shadows, in the virtual world of your model. Careful manual entry of your site-specific data insures true-to-life accuracy in your shadow study. The necessary tools are native to both SketchUp 7 and SketchUp 7 Pro.

Accuracy

How precisely your shadows correlate to the real world depends upon the accuracy of the location, direction and time data you enter. The GIGO principle applies!

Shadows and the Ground Plane

Right click on any Drawing Axis to display the Axes Context Menu and select "Reset" to restore their default location. The plane where the red and green Drawing Axes lie is called the Ground Plane. Position your model on the Ground Plane and select, Display: On Ground, in the Shadow Settings dialog box.

Positioning your model above or below the Ground Plane will distort shadows cast "On Ground". If your model portrays terrain that is not a flat plane, turn off, Display: On Ground.

Information you'll need about the real world location you intend to portray in your model:

• • Latitude — Decimal Degree Format

  • Longitude — Decimal Degree Format

  • Time Zone — Your local time offset ± from UTC (Coordinated Universal Time)

• Model Orientation — Determine (in degrees) the exact relationship between your model and real world North you wish to portray.

Later on, you will use that relationship to set the North Angle, which establishes the real world orientation of your model with SketchUp's shadow engine.

Normal Method

In the Set Custom Location dialog box, SketchUp provides a straightforward series of data entry fields for entering your custom Geolocation data.

Alternate Method

Add a location to the Locations.dat file. This method creates a preset custom geographic location and time zone setting, thereafter available in the drop-down list boxes in the Model Info-Location Panel.

Where to Enter Geolocation Data—Normal Method

Where to Enter Geolocation Data—Alternate Method

Add a new location to the locations.dat file to create a convenient preset geographic location and time zone setting. Once properly entered in the file, the new custom location appears in the Country: and Location: drop-down list boxes in the Model Info-Location Panel.

Many countries utilize fractional hour time zones, e.g. Central Australia is +9.5, India is +5.5 and Venezuela -4.5. This method is the only means of entering a custom location with a fractional hour time zone setting.

File Location

PC

C:\Program Files\Google\Google SketchUp 7\Resources\en-US\locations.dat

Mac

SketchUp 7 Show Package Contents > Contents > Resources > English.lproj > locations.dat

Open With

· PC - WordPad

· Mac - TextEdit

Data entry format

Enter your new location data in the exact same format as the existing file entries. Note that Longitude is entered before Latitude; counter to the order they are normally written. Maintain the alphabetical order of the Country and Location entries in the file to make your new entries easy to find in the drop-down list boxes.

The Country and Location entries in the locations.dat file are merely labels. Thus, you may create your own unique labels to organize and identify your new entries.

E.g. “My Locations”,”My House”,-89.600,46.200,-6.00

Highlighted in the example below is a new entry in the locations.dat file for Boulder Junction, Wisconsin.

Your new custom location will now appear as one of the preset selections available in the Country: and Location: drop-down list boxes in the Model Info-Location Panel as shown in the example below.

Move on to the last parameter to set, the North Angle.

The North Angle establishes the direction of real world True North in relation to your model.

In the Model Info - Location Panel, use the Up/Down buttons to adjust the value or click in the North Angle Field to enter a value with the keyboard.

Click the Show in model checkbox to view the bright orange axis of the North Angle, indicating real world True North in relation to your model.

North Angle Tool — Cursor tool for setting the North Angle.

Click the Select button next to the North Angle Field to launch the North Angle Tool and the cursor becomes a simplified compass rose with real world north highlighted as a heavy black axis.

Click on the drawing origin and swing the black axis about with the mouse. Note the heavy black tool axis functions in unison with the orange axis of the North Angle and its numeric value in the North Angle Field. A second click sets the North Angle, thus establishing the direction of real world North in relation to your model.

It is not necessary to select the drawing origin as the first point of orientation when using the North Angle Tool. The tool utilizes SketchUp's inferencing engine. Thus, if the drawing origin is in an inconvenient location, you may position the tool and set the North Angle anywhere in the model, by simply inferring to a meaningful entity in your model as a reference for orientation to real world North.

A closer look at Location, Direction, and Time...

— Finding and Entering Latitude/Longitude Coordinates in Decimal Degrees.

Latitude and Longitude Data Fields

Several formats are commonly used to express Latitude and Longitude.

The three different format examples below all represent the same place on Earth, i.e. SketchUp’s default location in Boulder, Colorado, USA.

In the Set Custom Location dialog box, the Latitude and Longitude Fields accept coordinates entered in Decimal Degree Format ONLY. Up to four decimal places are accepted.

In terms of accuracy, 0.0001° of Latitude equates to a distance of slightly less than 37 feet. See: Decimal Degrees | Precision — Wikipedia

Enter your Latitude and Longitude values, each preceded by the appropriate plus sign (+) or minus sign (-) or enter each coordinate followed by the appropriate indicator of direction N, S, E, W. Either method of entry is correct, as shown in the examples below.

40.0170N 105.2830W <<<<< is equivalent to entering >>>>> +40.0170 -105.2830

Finding Latitude/Longitude in Decimal Degrees using Google Earth.

Avoid the confusion of converting ... Read this before you use Google Earth to find your Latitude/Longitude coordinates.

By default, Google Earth presents Latitude/Longitude coordinates in Degree · Minutes · Seconds format.

Unfortunately, SketchUp only accepts Latitude/Longitude coordinates entered in Decimal Degree format.

Google Earth will display coordinates in Decimal Degree format by simply changing a display setting.

In Google Earth: Select - Tools > Options > 3D View, then select Decimal Degrees in the Show Lat/Long Panel, click Apply, then click OK, to close the Google Earth Options dialog box.

— Virtual North, Real World North, and the mechanism used to relate them in SketchUp, the North Angle.

Direction in SketchUp

Like True North in the real world, Virtual North in SketchUp is an inalterable Direction.

The orange North Angle axis is an adjustable indicator of direction. It signifies real world True North.

The Drawing Axes are infinitely adjustable references to direction.

Drawing Axes and North Angle are independently adjustable. Each is merely aligned with Virtual North by default.

Default Relationship of Virtual North, Drawing Axes and Orange North Angle Axis

SketchUp provides several ways to determine Virtual North:

Visual

• • To simply look north, select Camera > Standard Views > Front

• • By default, the solid green drawing axis is aligned with Virtual North.

    • However, if you move the drawing axes, the solid green drawing axis may become misaligned with North. Right-click on a drawing axis to display the “Axes Context Menu” and select “Reset” to restore the default.

• • By default, the bright orange axis of the North Angle is aligned with Virtual North.

    • However, if you move the orange axis or change the default (0.0°) value in the North Angle Field, the orange axis becomes misaligned with Virtual North.

North Angle

To create accurate real world shadows, SketchUp requires the direction of real world North in relation to your model.

SketchUp's shadow engine then utilizes your indication of real world North as its directional reference for calculating shadows.

The North Angle is the mechanism in SketchUp used to set the direction of real world North in relation to your model.

The bright orange axis of the North Angle always represents real world True North in SketchUp. It is the directional reference to real world north employed by the shadow engine. Aligned by default with virtual North, it can be set to any horizontal direction in relation to your model.

North Angle Field

— Setting the North Angle by the numbers.

The term North Angle also describes the value displayed in the North Angle Field, found near the bottom of the Model Info - Location Panel.

While Virtual North in SketchUp is inalterable, the orange axis of the North Angle is adjustable. The value displayed in the North Angle Field is the angle between them, measured clockwise from Virtual North to the orange axis of the North Angle. Changing the value in the North Angle Field from its default 0.0° setting, swings the orange axis clockwise away from its default alignment with virtual North in SketchUp, towards alignment with the real world North orientation you choose to portray in your model.

Because its basis is the inalterable Virtual North, it provides a stable reference and accurate numerical control for setting the direction of real world North in relation to your model, regardless of how the drawing axes may be oriented.

To view the orange North Angle axis, click the Show in model checkbox in the Model Info - Location Panel.

Notice the default value in the “North angle:" field is 0.0 degrees, which signifies the orange North Angle axis (Real World North) is aligned with Virtual North in SketchUp.

True Direction and the Compass

SketchUp calculates shadows with reference to real world True North.

If your shadow study involves fieldwork with a compass, failure to understand and accommodate the difference between Compass Direction and True Direction will introduce significant error. Compass Direction seldom coincides with True Direction.

Earth’s magnetic poles are misaligned with the geographic poles that define True Direction.

Moreover, Earth’s magnetic fields are by no means uniform. Thus, the amount of misalignment changes significantly with location — ranging from 0° to amounts greater than 45°.

This misalignment - called Local Magnetic Variation (or Magnetic Declination) - is easily reconciled by applying Corrections to convert Compass Direction to True Direction or vice versa.

Correcting Direction merely requires the appropriate addition or subtraction of Variation.

Variation is expressed as an amount in degrees East or West of True North, e.g. 15°W or 20°E.

Whether you add or subtract depends on whether the Variation is East or West and whether you’re correcting from Compass > True or from True > Compass. Simple rules apply.

EXAMPLES

True > Compass - Variation is East

Local Magnetic Variation (v) is 15°East or 15°Ev

Your known True Direction (T) is 45° or 45°T

Find the Compass Direction (C) of the True Direction

Beginning with a True Direction, the illustration shows we subtract East Variation from True Direction to arrive at Compass Direction, thus … 45°T - 15°Ev = 30°C

True > Compass - Variation is West

Local Magnetic Variation (v) is 15°West or 15°Wv

Your known True Direction (T) is 45° or 45°T

Find the Compass Direction (C) of the True Direction

Beginning with a True Direction, the illustration shows we add West Variation to True Direction to arrive at Compass Direction, thus … 45°T + 15°Wv = 60°C

Compass > True - Variation is East

Local Magnetic Variation (v) is 15°East or 15°Ev

Your known Compass Direction (C) is 45° or 45°C

Find the True Direction (T) of the Compass Direction

Beginning with a Compass Direction, the illustration shows we add East Variation to Compass Direction to arrive at True Direction, thus … 45°C + 15°Ev = 60°T

Compass > True - Variation is West

Local Magnetic Variation (v) is 15°West or 15°Wv

Your known Compass Direction (C) is 45° or 45°C

Find the True Direction (T) of the Compass Direction

Beginning with a Compass Direction, the illustration shows we subtract West Variation from Compass Direction to arrive at True Direction, thus … 45°C - 15°Wv = 30°T

— UTC, Local Time, Sunrise/Sunset, and the mechanism used to relate them in SketchUp, the Time Zone Setting.

Years, Months, Days, Hours, and Minutes — Each has a setting.

Select Window > Shadows to open the Shadows Settings dialog box.

Setting the Month, Day, Hour, and Minute in the Shadow Settings dialog box is a straightforward process, leaving little to the imagination.

Setting the Year is easy to overlook.

Click the arrow button in the Date Field to view the calendar.

Click on the text indicating the year (2002 in the example below) and the Up/Down Year buttons appear.

Click on the text indicating the month and a convenient 12-month menu appears.

Click on Today at the bottom of the calendar and the Year, Month and Day become the current date on your system.

Time Zone Setting

Setting the time zone in the Set Custom Location dialog box establishes the correct relationship between solar time in your model and real world local time.

**The goal is to have the sunset and sunrise times indicated in the Shadow Settings dialog box, correspond with the local time they occur in the real world.**

Standard Time zones can be defined by dividing the Earth into 24 wedge-shaped sections, bordered by meridians each 15° of longitude apart. The local time in neighboring zones would differ by one hour. However, political boundaries, geographical practicalities, and convenience of inhabitants can result in irregularly shaped zones. Moreover, in a few regions, half-hour or quarter-hour differences are in effect. http://en.wikipedia.org/wiki/Time_Zone

Note: You must use the Alternate Method to setup a custom location with a fractional hour time zone.

See: Where to Enter Geolocation Data—Alternate Method

Time and Longitude

The chart below illustrates the Standard Time relationship of longitude and time zone.

Use it to determine your Standard Time UTC zone by locating your longitude between those meridians shown in the chart.

When using this method to determine UTC offset—

Further adjustment of the time zone setting in the Set Custom Location dialog box may be necessary to synchronize with an irregular time zone or to adjust for local observance of Daylight Saving Time.

Note: Changing the time zone setting has no effect on the accuracy of projected shadow angles for a given geographic location. The time zone setting merely alters the local time of sunrise/sunset at a given location.

— Links to Reliable and Interesting Sources

Complete Sun and Moon Data for One Day (Location Specific Worldwide Data)

United States Naval Observatory - Astronomical Applications

http://aa.usno.navy.mil/data/docs/RS_OneDay.php

Magnetic Declination Calculator (Location Specific Worldwide Data)

National Oceanographic Atmospheric Administration - National Geophysical Data Center

WWW.TimeandDate.Com Global UTC reference site for finding your local UTC time data.

http://www.timeanddate.com/worldclock/

Russia Eliminates 2 Time Zones March 28, 2010

Further manipulation of time zones appears likely.

Shadow Studies

George Knowles