There is a good thread in the SL Forum for those that are interested in making to-scale objects with Blender. See: Getting a good measurement for SL within Blender.

Blender Units – by Aquila Kytori

Codewarrior Congrejo makes a suggestion in the thread that I use in my modeling. Put an avatar in the scene. I strongly urge furniture makers to go to the trouble to do that. I literally do not have ANY furniture that fits my avatar. Couches are ridiculous. The distance from the face of the back rest cushion to the front edge of the seat can be a couple of meters. WTH?

There are bits in the forum thread that may surprise even experienced Blender users.

To set the units in Blender, look in the Properties panel, normally the one along the right side. Notice the button selected in the image above.

I suspect most of us work in Blender with NONE selected for units as it is the default. Most tutorials assume you are using none too. Basically a Blender Unit equals 1 meter. If you think that way things are pretty simple.

If you are thinking of using Blender Units as Imperial units, feet, I suggest you don’t. You will have some scaling problems as you bring things into Second Life™. If you think of a Blender Unit as an inch, that is going to be a problem. Your model is going to come out about 100 times too big.

To avoid that, consider. Blender works with non- denominational units (period). To Blender it is just a number. So, something 2.18 BU (Blender Units) is numerically always 2.18 in Blender. If you want to think of that unit as light-years or nanometers you can. Blender does not care. However, Blender can display units and allow you to think of them however you want or as Metric or Imperial. Blender can display all three, but only those three.

This means if you are thinking of a unit being a light-year, Blender cannot do a conversion and display it.

If you change Blender to display meters it displays 2.18 units as 2.18m. If you change it to Imperial, it still 2.18 Blender Units but Blender displays it as 7.152’. Blender is just doing math to convert 2.18 to display 7.152’. Blender is using 2.18 internally.

Same Coordinates in All Units

So, if you have to work in Imperial, don’t think of Blender Units as inches, feet, or yards. Think of Blender units as meters. Change the setting in Blender to display Imperial. Blender will then handle the units conversion for you. BUT, it is a display ting only.

Changing to Imperial is fine until you start to deal with other parts of Blender like the grid, snap, or scaling. Things can get confusing when changing the units as the grid, snap, and etc. seem a bit odd to me. You may have to change those manually to fit your workflow.

It is key to remember: it does not matter to Collada whether you select NONE, Metric, or Imperial. It exports the exact same file. At least in Blender 2.67b it does. Changing units does not change the coordinate values of the vertices. So, going from any Blender units setting to Second Life should work OK as long as you think of Blender Units as meters and use the Blender settings to display Imperial.

The problem is avoiding getting confused and over thinking things or not changing the units to display your unit of choice. If you think of a Blender Unit in Blender as anything other than a meter, you are likely to have problems.

Some think they have to convert their Imperial units in Blender to meters before importing to SL. Not so. That can mess things up, if you thought of Blender Units as anything other than meters and did NOT change the units display, you have a scaling problem. In this case you will have to do a conversion and set a scale factor when importing to Second Life.

If you have to work in Imperial units, just remember it is a display thing only and that internally Blender and SL always work in metric and unless you do something to upset that, like use Blender Units as feet, inches, or centimeters, it is just magically handled.

Avoid the brain damage and use Blender’s Units Display setting.