Boolean Geometry Operations

DesignBuilder provides some powerful modelling tools for combining blocks in various ways to create new more complex geometric forms. Boolean geometry (otherwise know as Constructive Solid Geometry or CSG) provides these functions:

 

 

The boolean process works in 4 stages:

 

  1. Select the 2 blocks involved. The union operation can be applied to any block including building blocks, component blocks and outlines blocks but the Subtraction and Intersection operations can only be applied to outline blocks as they require intersection of the 2 primary blocks. The 2 blocks must both either be of the same type (building block /component block /outline block) or must involve an outline block. They must touch in the case of the Union operation and intersect in the case of the Subtraction and Intersection operations.
  2. Click on the Boolean operations toolbar icon. This opens the Drawing options dialog in the bottom left of the screen.
  3. Select the operation type in the Drawing options panel in the bottom left of the screen. In the case of 2 building blocks Union is the only option so the drop list is greyed out. The 2 blocks are both shown in purple for the Union and Intersection operations, or one in purple and the other in green for the Subtraction operation. For the Subtraction operation the green block will be used to subtract space from the purple block.
  4. Left-mouse click a final time on the model to complete the operation.

Important Note: The Boolean tools are provided to help create geometries that cannot be created any other way. DesignBuilder Support recommends that you only use them for this purpose and avoid the temptation to use the union tool to reduce the number of blocks in a model. As a general guide, it is usually better to work with a number of simpler blocks than one larger block of complex geometry. The more complex the block geometry the more challenging the generation of the zone inner geometry and the more likely that DB will generate surfaces of zero thickness.

One specific case that sometimes leads to zone inner volume creation failing and surfaces having zero thickness is when more than 3 surfaces are adjacent to a vertex. This is more likely to happen with blocks of complex geometry. It is not such an issue for EnergyPlus simulations because DesignBuilder is still able to account for surface thickness when calculating zone volumes and floor areas, but it can be a real issue for CFD which requires any internal surfaces to have non-zero thickness.

Note that the zone merge tools are the preferred method for creating zones spanning multiple blocks.

See also the Outline blocks, Boolean operations tutorial

 

 

This example illustrates how to create geometry with one ellipsoid (egg-shaped) block within another.

 

Step 1 Draw 4 construction lines starting from origin to create a cross centred on the origin 20 x 10m

 

 

Step 2 Draw a dome 20m radius centred on the origin, then use the Stretch tool to reduce it's y and z dimensions by 50%. The dimensions should be 40m in the x-direction, 20m in the y-direction and 10m height (z-direction).

 

 

Step 3 Draw a similar but 2x smaller ellipsoid 10m x 5m x 5m. Move the large ellipsoid on top of the smaller one with the centre of each over the origin as shown below.

 


Step 4 Use the selection tool to rubber band a selection over both blocks, click on the Boolean operations toolbar icon and select the Subtraction option in Drawing options. If necessary click on the Switch subtraction block checkbox to ensure that the smaller inner block is in green (i,e. it is to be used to subtract volume from the larger block). After the Subtraction operation you should see the blocks as below.

 

 

and with the smaller inner block moved out of the way:

 

 

Step 5 Draw a small rectangular outline block aligned with the x and y axes to give you a vertical plane to allow rotation operations to create the lower blocks. Then copy the larger outer block and rotate the copy by 180° using a vertical plane as the rotation plane. Repeat these steps for the smaller inner outline block.

 

 

Step 6 Position and Union the 2 small inner blocks together to create an egg shaped inner block.

 

 

Step 7 Move the inner outline block into place.

 

 

Step 8 Convert the outline blocks to building blocks

 

 

Step 9 Move the lower outer block into position.

 

 

Step 10 if necessary, move the entire set of 4 blocks above ground by selecting all 3 blocks (rubber band selection) and using the base point of the lower outer block as the reference point and moving it the origin.

 

 

Step 11 Set 100% glazing for exterior, interior and roof glazing.

 

 

 

Step 12 Draw 2 holes in the floor of the outer top block. Note it is not possible to union the 2 outer blocks as there would be problem maintaining the inner blocks in this case.

 

 

Step 13 Visualise and simulate.

 

 

 

The first step in using the Boolean operations is to go to building level and select the 2 blocks to which the command is to apply.

 

The 2 blocks to be combined are shown above before the operation is started- a 3.5 m height L-shaped block and a tall sports hall block.

 

 

When the 2 blocks are both selected the screen looks as above with the Boolean operations toolbar icon enabled.

 

Pressing on the toolbar icon at this stage starts the command and the Display options panel is displayed in the bottom left of the screen. On this panel there is a drop list with the 3 Boolean functions available for selection. In the case where 2 building or component blocks are selected, only the Union operation is allowed. This is because building blocks cannot intersect and the Subtraction and Intersection options do not apply as they require blocks to intersect.

 

 

Once the command has been started the 2 blocks will become purple. To complete the operation, left-click once more on the edit screen with the mouse.

 

After the final click, the 2 blocks are joined into a single block (above).

 

This can be a very useful way to simplify building geometry avoiding use of multiple blocks and easing the creation of zones that may span what were multiple blocks.

Note: When combining 2 adjacent blocks using the Union operation, block boundary walls are not replaced by partitions for abutting vertical surfaces.