> In the 3D view maybe the vertical axe from a point of a start of guide lines will be useful

You mean vertical as in the z direction up from the plane? You can create such a one by doing a second guideline snapping the first point on to the start of the original guide line.

Construction lines are the way that you can place points in the 3D view up off the plane - just drag it along the zaxis line to create a z guide line. Let me know if this doesn't make sense.

> Another curious question on the image linked always about drawing Guide lines :)

That shows up after you create a construction line and gives you some more options - move the mouse over it to highlight it, and press and hold down on it for a moment to activate the menu. It doesn't activate on a simple click so that it doesn't interfere with regular picks, you have to hold down on it for a moment.

That menu lets you relocate the construction line somewhere else or also reorient it to point towards a new location. This allows you to use the construction line as a type of measuring stick - you can capture a line and then relocate it somewhere else for parallel constructions, or capture a distance and point it towards somewhere else to provide the same distance in a different direction. The last option is to project the next point - this can be used for example to match the elevation of an existing object. Say for instance you have a cube and you want to draw a line that starts somewhere else on the plane but comes up with the same elevation as the top of the cube. Pull up a z construction line in the 3D view, and then activate projection, then you can move to snap to a point on the cube and it will be projected to that line.

Let me know if you want more details on any of this. This is an area that I'm planning on doing one of those Camtasia screen captures to help illustrate, there is actually even more precision drawing features available with these construction lines, like you can use them to mirror a single point around a particular axis.

- Michael