Maxsurf has the ability to display background images in each of the design views. Those in the Plan, Profile and Body Plan views may be re-positioned and resized to match the design and can then be used to assist in fairing to an existing design. The image in the perspective view is always displayed at full image size and from the top left corner; by using the zoom and pan control you can re-position your vessel in the scene.

Maxsurf has no built-in image manipulating commands, other than to control the position and scale of the image. Hence you must ensure that the image is in the correct orientation prior to loading into Maxsurf. It is also helpful if you make the background colour of your image similar to that of the Maxsurf background colour, since it will be easier to see the control points and other lines which are drawn over the top of the image by Maxsurf.

When scanning the lines plan it is important to do this at a reasonably high resolution to minimize any digitizing errors. In this document, scanning refers to the process of creating a bitmap image (such as a jpeg or bmp file) from a paper drawing, while the term digitizing refers to the creation of a point in 3D space (i.e. having x,y and z coordinates) from information on a scanned drawing.

It is also important to make sure that the scanned image is not rotated relative to the screen, this will make it extremely difficult to digitize accurately. If you find that your image does have a slight rotation, it is necessary to correct this in a paint program such as Photoshop or Paintshop Pro prior to importing it into Maxsurf.

Maxsurf can load image files of the type jpg, gif, bmp and png. Once you have a suitable image of for example your body plan

Ø  Open Maxsurf and select File| New Design… from the file menu.

Ø  To import the image, switch to the body plan view and select File|Import|Image Background…

This will import the image in the Body Plan window.

When first opened, the image will be scaled so that it is displayed at full size at the current window zoom level. Once you have loaded the image, you can re-position it by locating the zero point in the image. The image will then be moved so that the image zero point is in the same position as the design zero point.

The next step is to centre the image in Maxsurf’s coordinate system. To do this,

Ø  Select Display | Background | Set Image Zero Point.

Ø  Zoom in and click on the point on the image that you wish to be the zero point.

The most likely location for this example image is the intersection of the centreline with the DWL or the baseline. For an image in Profile you may pick the Aft Perpendicular and the same DWL or Baseline.

When you click the mouse, the background image will move so that the point you just clicked lines up with the design's zero point:

You can specify a known position on the image to scale the image. To do this you only need to know the value of a single dimension on your drawing in either the horizontal or vertical direction. For most drawings this is trivial as they will have a known waterline and/or buttock spacing and these can be directly measured.

Ø  Select Display| Background | Set Image Reference Point.

Ø  Zoom in and click one of the waterlines, preferably the one that is the greatest distance from the DWL.

A dialog will appear asking you to specify a value for this distance. For example, if you know that your waterline spacing is 1.5 meters, and you clicked on waterline 3, enter 1.5 m.

Ø  Make sure that the Direction item has Vertical selected and click OK.

See the Maxsurf Coordinate System on page 14 for information about UCS directions and sign conventions in Maxsurf.

Note that the aspect ratio of the image is always maintained.

Images in all the views are independent so you can load a profile and buttock lines sketch into the Profile view, a sketch of the sections into the Body Plan view and a sketch of the waterlines into the Plan view.

The next step is Setting up the Grid, see page 19 of this manual.

Note that Maxsurf uses a coordinate system that increases in value towards the bow, so if your station zero is at the bow, and you wish your profile view to have the bow on the right hand side, you will need to have the negative values for the station locations. If you place your zero point at the transom, station locations will be positive values.

Once you have specified the station spacing and clicked OK, it is likely that the Inset Box in the top right corner of the Body Plan window will be blank. This is because there are no surfaces specified and Maxsurf needs to be forced to rescale its internal viewing parameters so that the station locations will appear, scaled to the length of the Inset Box. To force this to happen,

Ø  select View | Home View.

Small marks should now appear at the top of the Inset Box corresponding to the locations of the stations. Click on the right most of these marks – a black vertical line should appear below it –

Inset box in top right of Maxsurf Body plan window

You have successfully selected station zero of your background grid as the current station. This sets the longitudinal position of any point you digitize in the Body Plan view, providing the third value of the x, y, z coordinates for the point.

The next step is to select the Add Marker tool and click on a point on the section at station zero. The most efficient way to do this is to drag the Markers Toolbar onto the Body Plan window so that you can repeatedly select Add Marker. Alternatively, Add Marker can be selected by using the Ctrl-M key combination.

You can now add marker points for as many points on the section as you like. Remember that you can use the zoom tool to zoom in as far as you like when adding markers to get the most accurate points possible.

Once you have finished digitizing the points for station zero, click on the indicator for station 1 in the inset box. This sets the longitudinal position of any subsequent markers that are inserted to the location of Station 1. In this way we build up a three-dimensional set of marker points, rather than just a two dimensional dataset.

Again, digitize the points for the section at that station location. It helps if the drawing is clearly labelled with the station number, as in this example, as it is very easy to get the longitudinal location confused and accidentally digitize a section at the wrong longitudinal position.

Continue digitizing points for each section, then selecting the next station location until all stations have been digitized. If you now switch to the perspective view, you should find that you have a complete, three-dimensional set of data points entered for all the stations.

If you have a profile view scanned, you can now switch to the Profile View window and perform the same process. In this case you are probably just interested in the bow profile, and this is easy as the marker points you insert will be added on the centreline.

Import your image as before, set the zero point to the intersection of the DWL and Station zero, then set your scale by selecting the position of one of your aft stations and entering its location in the Reference Point Dialog. In this case remember to select Horizontal for the measurement direction.

You can now proceed with the digitizing of the bow profile, and this will be added to your set of marker points.

Also see:

Fitting a NURB Surface to Markers on page 155.

Working with Markers on page 68

The background image in the Perspective view can be used for generating presentation pictures. The background image remains in the centre of the screen, use the zoom and pan controls to place the Maxsurf design in the desired position over the background:

Note that the images are not saved with the design file, only the path name to the image file. If you change the directory of your images or their file names, Maxsurf will no longer be able to find them and the images will not be automatically loaded when the design is re-opened.