COMPUTER AIDED ARCHITECTURAL DESIGN
 Workshop 10 Notes, Week of November 9, 2009

Editing by Projection, Fence Tools, Cutting Solids with Surfaces, GC Examples with Functions

PART I: FENCE TOOLS

Fence tools allow you to select a portion of a view window and to perform operations on it, such as editing, deleting, moving, copying, rotating, scaling or stretching geometrical elements.  You can also render a sub-portion of a window through the use of  a fence tools. The fence tool is projected into the view window to perform these various operations.

1. COPY AND CLIP OPERATION
Within MIcrostation V8i, start a new drawing, open the  Utilities>Auxiliary Coordinates dialog box. Use the save ACS  icon in upper left-hand corner and save the current default ACS plane as "base".


Turn on the ACS PLane lock by opening the padlock symbol at the lower part of the screen. Next, use the Solids Modeling, "Slab Solid" tool to create a solid slab on the ground plane.

Select  the front view (View 3) and use the "Define auxiliary coordinates by view" icon , highlighted in  the Auxiliary Coordinates dialog box below (7th icon from left-hand side), to create an ACS in the front view window.  

  

 Save the new ACS as "front" within the Auxiliary Coordinates dialog box.



Open the fence tools subpalette from the main task menu (#2 key).


Draw a "Fence"  in the front view window with "Fence Mode" set to "Clip". This mode isolates what's inside the fence from the outside.



Select the "Manipulate Fence Contents Icon"  (second icon in the Fence palette) andnthe "Move" option,  and enter two data points in the front view with to clip off and move upward the geometry that is encompassed within the fence. This is a quick boolean operation. Here we are working from a 2D projection of the fence onto the objects from the view plane.





Similarly, select the top view window. Select the "base" ACS form the Auxiliary Coordinates Dialog box,  and repeat the same move operation on the upper "Y" axis portion of the cubes from the top view.

The result of the preceding two operations is to splice the slab into four slabs. Note that the fence tool in the top view operates on  upper visible slab as well as the occluded lower slab in that view. That is, the fence projects the operation entirely through every object in its pathway in that view.

2. STRETCH OPERATION

Re-select the front view, then select the "front" ACS in the Auxiliary Coordinates dialog box, and place the fence over the slabs in the lower portion of the view window.  Next use the "Manipulate Fence Contents" and  "Stretch" tool option (shown below)  to change the height of the cubes on the ground plane..

Once again, the fence projects the operation entirely through every object in its pathway in that view and they are stretched to have a larger "Y'" dimension. Note that a truncated cone (not shown) in similar situation would also have stretched in a tapering way preserving its tapering geometry. Similarly, other objects will also stetch appropriate to their geometry.

3. NON-RECTANGULAR FENCE

Select the "Front" view and then the "front: ACS from the Auxiliary Coordinates Dialog box. Next, select the" Fence" tool,  change the fence  type to "Shape",  and draw an arbitrary polygon over the front view.

Zoom out of the  "Front" view and use the "Manipulate Fence Contents/Move" option to clip the arbitrary shape to a location above the slabs. Note that the operation cuts the arbitrary shape out of the cubes and moves it above them.

3. RENDERING WITH THE FENCE TOOL

In View 2, draw a "block" Fence over a portion of the view window. In the Visualization task, adjust the solar lighting using the W1 tool,  select the "Render" (Q1)  tool, and choose the "Fence" option. The result is that a smaller sample portion of the view window is rendered. This can be a very efficient way to sample the rendering quality without having to expend much greater time in testing the entire view window. Note that rendering 1/4th of the view window in Ray Trace will be significantly faster than doing the whole view.

Note that the Render dialog box also allows you to render individual objects in several render modes, such as Phong or Smooth shading. This is achieved by selecting the third icon in the "Render" dialog box as depicted below. However, this doens't work in Ray Trace mode (since the rendering algorithm is based on backward tracing of rays for every pixel in the rendered area).

PART II: EDIT BY SURFACE PROJECTION

 

Erase the current elements in the model, and place a rectangular block and a bspline curve in the ground plane. Next, within the Solids task, use the projection tool (T1)to project the bspline curve into the vertical direction.

Place a slab in the model so that it is fully encompassed by the new surface.



In the Surfaces task, sleect  the "Trim Surfaces" tool (S1) and select the "Trim 2nd" option, then pick the surface first and the slab second. Enter an additional data point in the view window to initiate the trim and a fourth data point to confirm it.  Note that a portion of the slab is trimmed away.
 

The reverse part of the slab is trimmed away if the "Flip 2nd' option is turned on.

The surface trims the slab according to the direction of its surface normal vector (the positive side of the surface). This vector can be reversed through the use of the "Change Surface Normal" tool(S6) in the "Surfaces" task(image at left below). Selecting the green surface normal arrow will reverse its direction. Completing this step and re-doing the trim surface operation will reverse the portion of the slab that is trimmed away.

PART III: GC FUNCTION EXAMPLES (EXTRACURRICULAR)

The two examples presented here go slightly beyond the scope of our basic introduction to generative components and incorporate "function" update methods that contain "while" loops.

1.  Spiral

The GC example spiral2.gct draws and archimedes spriral that can be transformed into an accelerating spiral. A number of graph variables are defined in the first step of this GC file according to the methods examined in earlier workshops. The variables determine the resolution, scope and size of the spiral:

numsides = number of sides in each 360 degree spiral
numspirals  = total number of 360 degree spirals
radius = radius of initial spiral
angleincrement = incremental angular distance between points in a given spiral ( = 360 / numsides)
deltaradius = accelerating rate for the radius from spiral to spiral

Note that if deltaradius = 0, then the spiral is an archimedes spiral. If delatradius > 0, then the spiral accelerates.




In the second step, the GC file incorporates a polygon line " Function" update method, essentially a short algorithm that handles the generation of the spiral.  



 When placing the mouse in the textbox containing the function arguements "{angleincrement, numsides, numspirals, radius, deltaradius}", the function arguments can be more closely examine by selecting the text editing icon (a small rectangle next to the "fx" symbol) that appears on the right hand side of the "FunctionArguements" textbox below.



Note that the arguments are set off by a left and right curly bracket.  These are the same variables that were defined in the first step of the GC file.



SImilarly, when placing the mouse in the Function textbox adjacent to the words "Function (double angleincrement, double numside ... },  the function update method can be examined more closely. The details of this function are somewhat beyond the intentions of this quick summary, and so a brief overview is given here only.

The arguments to the function are all given a type "double" declaration in that they are decimal numbers.  Additional integer "int" and "double" variables are defined internal to the function. The update method incorporates a "while" loop that continues to repeat when "curangle" of the radial point tracing out the spiral is less than then "maxAngle", the maximum angle of the final point in the spiral.   Note that "maxAngle = 360 * numspirals".  Inside the "while" loop,  as the point travels around the center of the spiral, the current angle and radius is continually updated. Each new point in the spiral is stored in a Point array named "ptLlist" . Thus, the first point is stored in "ptList[0]", the second point is stored in "ptList[1]" and so on.  When the loop is concluded, a polyline is created from the listing of points.




The use of iterative loops can efficiently express a condition in which an action is repeated continuously as is used to draw the spiral. Note, if the variable "deltaradius" is equal to 0, then the result of the above function is an Archimedes spiral.



If the variable ""deltaradius" is greater than 0, then the spiral becomes accelerating one.  



2. Daisy head

Similarly, the example file daisyseedfromFermat.gct incorporates a de-accelerating spiral according to a theorem by the mathematician Fermat. That is, the basis for the geometry is a Fermat curve. The code for this example after an algorithm initially published by Dixon. Placed along the loop are polygons that capture the pattern of seeds in a daisy head. The variables for the transaction file can control the tightness of the seeds together and the number of spirals as illustrated in the following three images.
tightness is high,  number of spirals is low tightness is low, number of spirals is low tightness is low, number of spirals is high