Hi Michael, triangles are 3 points only

When I select the two highlighted in my previous screenshot (they are separated before) and do a boolean union it union them correctly but the middle edge is still there so it's kinda making a join instead of a union :(

Here's 2 buildings exported

https://dl.dropbox.com/u/44982094/buildings.3dm

At first they were in a DXF file that I imported in Rhino, I couldn't export it as 3DM because it was not surfaces so I used two commands (explode) then surface to nurbs or something and that's were it made it into triangles. But then I was able to export them as 3DM.

Hi DesuDeus, you need to get the triangles to be made up of trimmed planes (with an underlying surface that has 4 points with the triangle being a trim curve on it), rather than made up of a surface that has one side collapsed down into a single point.

One way you could do that is to export that from MoI into OBJ format, then use the OBJ to 3DM wireframe converter here:
http://moi3d.com/wiki/Resources#Obj23dmWireframe_converter

Choose the mode for "One closed polyline for each face", then you will have a set of polylines that you can convert into trimmed planes using Construct > Planar in MoI. Then you will have the kind of planes that will get unified together when doing boolean union. It will probably not get 100% of them combined, it's more designed to unite a few coplanar box pieces together and not a highly fragmented sort of shattered set of triangles like this, but it should probably combine most of them. If you run into ones that don't combine try separating those out again and only select 2 pieces when doing the boolean union instead of a whole bunch.

In order to run the OBJ to 3DM wireframe converter on Mac, right-click on the MoI app and choose "Show package contents", and go to drive_c and make a new directory inside there called obj as a sibling to the moi directory. Unzip the wireframe converter into the new "obj" directory. Then back at the initial "Show package contents" level run Wineskin.app and go to Tools > Command line shell, inside the command prompt type cd \obj and push enter, and then type Obj23dmWireframe.exe and it should launch. Use the Z: drive inside there to find your Mac filesystem.

- Michael