Ethos Erlanger's First Virtual Life© Blog

Building in Virtual Worlds

Creating an Octagon Building in Second Life

Posted by Ethos Erlanger on April 16, 2009


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April 16, 2009

Creating an Octagon Building in Second Life

The true geometric term for this solid object is an octagonal prism.  However, for this discussion, we will simply call it an octagon rather than split hairs over the naming of geometric forms.  This is much the same as the way we describe The Pentagon that houses the United States Department of Defense offices in Virginia. That building should be called a pentagonal prism.  We are not wrong.  We are just builders, not mathematicians.

I have searched for this answer regarding how to build such a building for myself and did not find it.  I have made hexagon (six sided) gazebos and other hexagon houses before.  I have also used this technique for making a ten-sided (decagon) building with a domed roof.  The octagon building is made with the same techniques as any multi-sides building greater than four sides.  Even a four-sided square building can be made using these steps with only one modification.  The angles used to set the walls are dependent on the number of sides.  There are more steps to creating a pitched roof for the octagon building than there are for the walls, and I will cover the process of making roofs in a follow-up tutorial. Floors for these buildings are another matter, but we will focus on the exterior walls for now.

There are scripted tools available in Second Life to position prims, but this tutorial is intended to allow you to build the octagon using only the construction methods available from Linden Labs in their standard SL viewer.

I start by planning the size of the building.  Each of the 8 wall’s length can be made from one or more prims of any size, but I tend to build with walls that have dimensions of whole numbers.  The steps involved do not rely on any measuring, so the wall size would not change the steps involved. There will be 8 walls, each having the same length. Naturally, the wall’s height does not play a factor and the thickness of the walls does not play a factor in the steps that are used to build the octagon.

Let’s choose to use a wall length of 4 meters.  Remember, any wall length will work when a builder uses this method.  Create a prim that has that dimension along either the X or Y axis.  The Z axis (height) can be any value.  Let’s use 0.5 meters for the height. Another step I take when building is to always start with the first major prim at a location on the world building grid that is a whole number.  I take this step due to the tendency of the SL calculations for prim locations and sizes to be impacted slightly by a mathematical rounding error.  This step is not required, but it is a simple standard practice which makes it easy in many cases to check your results by looking at the coordinates of the position of your prims.

1)     Create and position the first wall section.

2)     Set its length to the wall dimension that you want each of the final walls to be as measured from the outside of the building.  I use the word length to mean the measurement along the wall as you face it, such as 8 or 10 meters.  Some other builders might choose the term width for this dimension.  Sometimes the word width can be confused with thickness, and a try to avoid confusion for the reader.

3)     Now, for the purposes of construction only, make the wall thickness twice the value of what you have planned for the final wall thickness.  You may either drag the prim side to make this wall depth, or you may enter it into the object tab of the edit window.  This thickness will be reduced back to the desired wall thickness in the final step.

4)     While in edit mode, set the building grid to Local.

5)     Using the shift-drag technique, create a copy of the first wall and position it at the 50% mark based on the wall’s length.

6)     Rotate this prim 45 degrees around the vertical axis (Z).

7)     Now that this prim is set to the correct angle, move it the final 50% distance so that it is at it’s final position along it’s centerline.

8)     Create the third wall in the same way, using steps 5, 6, and 7.

9)     Repeat this process for each of the remainder of the 8 sides of the octagon.

10)  Now that all 8 prims are set in their places, the last step is to reduce their thickness by dragging the outer face of each wall in towards the center of the octagon. This is still done with the building grid set to Local.  Because we doubled the wall thickness at the beginning in step 3) we will reduce that thickness to 50% of it’s current value now.  This should bring us back to the wall thickness that we decided upon during our planning stage of this process.

I have tested these steps and used them to build a number of multi-sided objects.  If you experience difficulty with these steps, then it is entirely my difficulty in communicating their intent.

Some time soon, I hope to make a video tutorial for these steps which will surely be easier to explain in a visual form.


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