Maxsurf has a straightening tool that will straighten:

1.      all control points on a row or column between two selected control points on the same row or column:

§    

2.      all control points on a surface patch defined by two diagonally opposite selected control points:

This straightening can be done either:

1.      From the current view direction. You will only see the control points on a straight line from the current view direction, but they will not be straightened from the other view directions.

2.      In 3D. The control points will be straightened in 3D; regardless what view direction you are looking from.

In the procedures below you will learn how this command can be used for specific purposes as well as its side effects.

 View a video that shows you how to use the straighten command to straighten control points on the deck edge of a containership followed by straightening the Flat of Sides area of the hull. [Web | Disk]

Straightening a row or column

Ø  Open the BasicFairing_FairingToolsStart.msd in profile view

Ø  Hide the Control point net

Ø  Switch the Compress display on

You should now see something like this:

Notice how the compress display suddenly shows that the top edge of the surface is not a straight line whereas in normal view this was difficult to see.

Let’s straighten this top edge:

Ø  Select the aft corner control point

Ø  While holding the Ctrl or Shift key down, select the top edge control point located at 68.5 m fwd of Aft Perpendicular (column 9)

Ø  Use the Controls | Straighten Controls | In Current Plane only command.

This results in a movement of the control points that lie between the two selected control points (A and B) in the direction perpendicular to a straight line connecting A and B onto that straight line. This straight line can be straight in 3 dimensions or a straight line from the current view direction only.

To straighten just one row or column, A and B have to be on the same row or column respectively.

Ø  Now switch to Plan view

Ø  Notice how this deck edge is  not straight in this view direction

We can fix this by repeating the command above for this view direction, or using a straighten command in 3D.

Ø  Undo the straighten command by using Ctrl+Z or reloading the design from the start of this section.

Ø  In plan view, select the Aft corner control point (A) and the edge control point at 68.5 m fwd of Aft Perpendicular (column 9) (B) again.

Ø  Use Controls | Straighten | In Three Dimensions

Notice how this has straightened all controls points between A and B in both Plan view as well as in Profile view. When you use Straighten in Three Dimensions, it does not matter which view window you are in as opposed to when using Straighten in Current Plane which only straightens in one direction.

Straightening a Surface Patch

The previous section you learnt how to straighten a row or column of control points

Ø  Continue with the model from the previous section, or open the BasicFairing_FairingToolsBowStraight.msd

Ø  Switch to Perspective view

Ø  Use the Transverse Curvature rendering

Ø  Rotate the model so that you see something like in the image on the left:

You can see that there is a transition from red into blue without any green in between at about midship. This should be the flat of sides (FOS) and thus coloured green (green = no curvature = flat). We can use a straighten command to straighten this panel. First let’s see how the straighten command works on panels, by making a “mistake”.

Ø  Switch rendering off and zoom in to the bow area

Ø  Switch the net on

Ø  Select the bow corner control point and a control point in the middle of the bow area like below:

Ø  Use the straighten in three dimensions command

You’ll see something like this:

This model can be viewed by opening BasicFairing_FairingToolsBowStraightEnd.msd

In the background, Maxsurf has done the following steps:

Step 1:

The area that the straighten command is applied on is determined from the selected control points. This can be called a patch of control points:

Step 2:

All four corner points of this patch are fixed in space and will not move. Patches selected by selecting two points on the Net are always four-sided and have four corner control points.

Step 3:

The edge control points are straightened between the corner points*

Step 4:

The internal control points are straightened between the edge points*

*same as for straightening a row or column, this can be done either in three dimensions or in the current plane only. The current plane in Perspective view is determined by the orientation of the model. In the bottom right hand corner of the Perspective window, there is a little orientation icon that indicates the current working plane. It is important to rotate the model in such a way that you have the correct current working plane when using the “Straighten in Current Plane Only” command as it will affect in which direction the control points are straightened.

Now let’s use what we have learnt so far to straighten the flat of sides panel:

Ø  Undo the last straighten command so that you get your regular bow shape back or load the BasicFairing_FairingToolsFOSStraight.msd file.

First we have to determine which control points we have to select in order to get a straight patch.

Ø  Switch transverse curvature rendering on and zoom in so that you can see the stern and midship.

Remembering what Maxsurf does in the background when straightening a patch of control points in step 2 (fixing the corner control points), it is important to know the location of the corner control points before using the straighten command:

Ø  Double click on all corner points of the patch as in the image above: A, AB, B and BA. Notice that they are all offset from the centreline by 9 m. This means that all four corner points are planar which is what we want for this flat of sides panel.

Ø  Switch rendering off in order to select the patch corner points A and B

Ø  Apply the Straighten in Three Dimensions:

We clearly see the flat of sides appearing after applying a straighten command

Notice how the shape of the control point net that forms the bilge-FOS line (from AB to B) has now become a straight line. This is not what we want.

Ø  Undo the straighten command

Ø  Rotate the model similar to the image below and switch rendering off

Ø  Selecting the same patch as before, now use a Straighten In Current Plane Only command:

This model can be viewed by opening BasicFairing_FairingToolsFOSStraightEnd.msd

You can see how the Straighten in current plane command maintains the shape of the Bilge – FOS line. This is because, when you rotated the model to the orientation as in the image, the current working plane was set to Body Plan.

Ø  Read the text directly below step 4 (above) again

Ø  Undo the change you just made

Ø  Rotate the model around the “Yaw” axis so that the orientation icon indicates that Profile view is the current working plane:

Ø  Now repeat the Straighten in Current Plane only command on the same control points A and B as before.

Ø  Notice how the Bilge – FOS lines is now a straight line and the transverse curvature transition is still there:

Although this is complicated to understand - and it is not expected that you do at this stage of the training -, perhaps the following images help you understand why the result of a Straighten in Current Plane is different when the current working plane is Body Plan view or when it is Profile view:

When the current working plane is Profile view, the control points between the corner points of the patch (in this case between AB and B) will move onto the straight line – as seen from Profile view - between AB and B perpendicularly.

Whereas, when the current working plane is set to Body Plan view, the control points snap to a straight line as seen from Body plan view and – in this case because all four corners were at 9 m offset from the centreline and the straight line is thus vertical – the control points all move horizontally inwards and outwards.

In case after reading the above, you still don’t understand (which is OK) just remember that:

§   You can use a Straighten command in Three dimensions and in the Current Plane only.

§   When you use the Straighten command in Current Plane only, the current working plane determines the outcome of the result.

If the result is not like you expected it you may want to try using another working plane by switching window, or rotating the model in Perspective view.

You may wish to repeat this tutorial a couple of times to work your way towards fully understanding this command.

Continue with the section on Smooth Control .