Unwrap3D Tutorial:

UV Mapping a Sailing Ship (or Anything Else)

Carl E. Schou

September 2004




The Santa Maria

In our previous tutorial, we built a model of Columbus' ship, the Santa Maria using Amapi 7 Pro.  For this month's installment, we are going to UV map and texture that model using Ultimate Unwrap3D and Photoshop.  The concepts and techniques used in this tutorial are applicable to a wide variety of different types of models, not just to sailing ships.  For anyone wishing to review the construction of the Santa Maria model, a link is provided in the Related Links section at the end of this tutorial.

We will start with a quick look at what UV mapping is, followed by the strategy for this project, and some tips on making models easier to UV map, before starting the actual work.



What is UV Mapping

UV coordinates are the “pins” used to attach a texture to a model, and UV mapping is the process of applying UV reference coordinates to a 3D model. These coordinates are used as a reference that controls how a flat 2D texture image will be wrapped around the model. You can choose mapping methods such as spherical or cylindrical that are closest to the original shape of your model but will probably produce some distortion.  The art of UV mapping involves adjusting the position of the UV coordinate on the map to minimize this distortion.



Strategy for UV Mapping a Model

(1) Build, borrow, or download a model that you want to UV map and texture.

(2) Import the model into UnWrap3D and UV map the entire model using the mapping that best fits the model.  For this project, single-sided planar mapping was used.

(3) If the model does not already have a material, create one in UnWrap3D.  Load a reference texture into this material to get visual feedback when adjusting the UV points to minimize the distortion in each group.

(4) Start with the simplest mapping first.  Map the parts oriented along the X, Y, or Z axis that need Cylindrical, Spherical, or Planar UV mapping.

(5) Map the off-axis parts that need Cylindrical, Spherical, or Planar UV mapping by using the Interactive Mapping tools.  These allow you to rotate the UV reference to align it with the part.

(6) UV map the irregularly shaped objects using the mapping that fits the best, then adjust the UV points to minimize texture distortion.

(7) Apply Box mapping to cube or box shaped structures, and manually align the maps where needed.

(8) Pack the map to get the most efficient use of space.

(9) Make your texture map and load it into the model's material.  Readjust UV points if needed.

(10) Export the UV mapped model in a format such as OBJ needed by your rendering application.



Modeling Considerations

Some models are relatively easy to UV map, and their textures are easily recognizable.  You can look at the texture map be able to tell how the map will fit to the model.  Other models are nearly impossible to make distortion free without applying techniques that unwrap the UVs or break up the maps into small sections, producing textures that are difficult to recognize or use without resorting to projection painting 3D texturing programs.  Here are a few tips for making models that are easy to UV map, and that can be textured with images right out of Photoshop.

Keeping the polygon count down can be a big help. Since the distortion is tuned out of a mapped texture by moving the UV points that correspond to existing vertices, keeping the polygon count down to a reasonable level goes a long way towards keeping a UV map manageable.  UnWrap3D has a Soft-Select option that allows for the editing of multiple points, but it is still simpler to move a single point than a large number of them.

A model with a complex shape that is a single group can be very difficult to map without distortion or splitting of the map.  Slicing the model into simpler shaped groups can simplify things greatly, and allow the use of basic mapping shapes with little distortion to correct.  If the borders of the groups correspond to seams in the model, it is that much easier to hide the breaks in the texture.

The neater the model's mesh, the neater the UV coordinates.  If you have a choice between using four point facets (quads) or three point facets (triangles), the quads are usually the better choice.  Whatever the facet shape, having all of the sides close to the same length will help to minimize distortion.  Long thin facets, especially triangles, can produce texture distortions that are nearly impossible to tune out.

Keep parts relatively straight before mapping.  It can be tedious to map an object that keeps changing its orientation.  To make life easier, build the model with the parts aligned along the X, Y, or Z axis, then apply UV mapping, then use your modeling program to put the bends and twists into your model.  An example of this approach is the flag in this model.  It was modeled flat, then planar UV mapped, then shaped as though it were flapping in the wind.  When the texture was applied, it followed the bends and turns turns in the flag with no distortion.



UV Map the Entire Model to get Started

If your model does not already have UV coordinates, then the first thing you will want to do after importing it into UnWrap3D, is to give it some.  We are going to assign a single sided planar UV mapping to our model.  Later on, the mapping of some parts will be adjusted, or they will be re-mapped using Cylindrical, Spherical, or Box mapping.

To apply the first mapping, select the entire model, then click on 2D Tools > UV Mapping > Planar > One Sided as shown below.




  The pop-up window should open as shown below.  Set the Axis Alignment as needed to match the orientation of your model.




  The resulting UV coordinates of all groups of the model are shown below in this screenshot from the UV Editor window.




  If your model does not already have a material assigned, you can create one by selecting the entire model, right clicking on Materials in the Scene window, selecting Add to add the material, then right clicking again to Rename it as shown below.  Later on, we will be adding a checker pattern to the material to use as reference texture for minimizing distortion, before applying the final texture maps.





Isolate Groups to Make an Uncluttered Work Area

The easiest way to work on any single part of a multi part model is to select all of the other parts, then move them out of the way to get a clear work area.  To do this, click on Select > Group, making sure you choose the second mention of Group in the drop down menu as shown below.




  In the pop-up window that opens, scroll down and select the one group you want to remain unselected as shown below.  To select all of the other groups, click Invert All, then Apply, the Close.  For our purposes, we are going to start with the ship's main mast, so we will select that, then invert the selection to select everything else.




  To move the selected UVs off the map, activate the Move UVs tool by clicking the symbol with the four arrows on the left side of the screen.  In the pop-up window that opens, enter a large, easily remembered value for the Nudge Amount, then click the button for the direction you want to move it as shown below.  By sticking with the same value for the Nudge Amount, you can easily move UV for any group into or out of the work area without having to zoom out your viewpoint and hunt for the parts.





UV Map the On-Axis Objects

Now that the map area is clear of all the UVs except for those from the group you are planning to map, it is time to invert the selection by clicking Select > Invert.  In this case, the main mast of the model is selected.  This part is easy to UV map since it is oriented along the vertical axis.  Click on 2D Tools > UV Mapping > Cylindrical to open the window shown below.  Set the Axis Alignment to Y and press Apply to generate the UV map.




  The resulting UV map of the selected main mast group should appear as shown below.  The facets in the UV map correspond to the facets in the model, unwrapped from their cylindrical shape and laid out flat.  Repeat this process with the other masts that are oriented on-axis.





UV Map the Off-Axis Objects

Most of the masts on this model are oriented along the X, Y, or Z axis, so they are easy to cylindrically map by setting the axis of alignment to the appropriate axis.  The masts that are at an angle may still be cylindrically mapped, but the orientation of the mapping needs to be rotated to line up with the selected object.  This is done with the Interactive UV Mapping option.  To use this, click Window > Interactive to bring up the menu as shown below.




  Clicking on Cyl in the Interactive Mapping menu should produce something like the two images below left.  The 3D modeling window will show a cylinder with red, green, and blue control handles centered on the selected part of the model.  The UV map at lower left is badly distorted.

To rotate the UV reference, go back to the Interactive Mapping menu and click on Rotate, then on XfmX to constrain the rotation to the X axis.  Click and drag in the 3D window to adjust the rotation.  When you have aligned the UV reference with the object, the UV map should straighten out as shown below right.





Apply a Reference Texture to Visualize the Distortion

The next part of the model to be mapped is the ship's hull, and it is the part that will require the most work to minimize any texture distortion due to its irregular shape.  The easiest way to see the distortion is to use a reference texture.  To apply this texture, double click on the name of the material in the Scene window to open up the Material Editor as shown below.  For the Diffuse channel, select Checker.




  Click on Properties and set the sizes for the tiling as shown below.  This should stretch the cubes enough that they almost appear to be horizontal stripes.





Minimize Distortion in Irregularly Shaped Objects

Now that a striped reference texture has been applied to the model, move any other groups out of the area, leaving a clear workspace to map the ship's hull.  In the upper Perspective view of the screenshot below, all parts except the hull have been hidden.  The UV mapping seen in the lower UV Editor window is the original single sided planar mapping that was applied to the model at the start of the project.  Notice that the reference texture looks like it was projected onto the hull with a slide projector.  It does not follow the sweeps and curves of the ship's hull.  Though it is not visible in this screenshot, extreme texture stretching was also occurring along the bottom of the model.




  The screenshot below shows the result of moving the UV points in the lower window to minimize the distortion seen in the upper window.  While this tuning was being done, the orientation of the stripes was occasionally changed from horizontal to vertical by switching the values given to the U and V tile sizes in the Properties window.





Apply Box Mapping to Any Box-Like Surfaces

This model has quite a few parts, such as railings and square posts, which are good candidates for Box (or Cubic) mapping as is shown below.  After selecting the top railing, Box mapping was applied to the groups as shown below left.  The different pieces of the map were then rotated to bring them all into alignment as shown below right.  The purpose of the alignment is to ensure that the wood grain image will map in the same direction along all faces of the railing. 





The Rest of the Mapping

The deck was planar mapped in sections with the axis alignment adjusted to match each section's orientation.  The sails were planar mapped and their UV points were straightened so that textures applied would billow out naturally with the shape of the sails.  The Crow's Nest was Cylindrically mapped.  To add the flag, the model was imported into Carrara where a flat flag was built and grouped with the ship.  Back in UnWrap3D, the flag was Planar mapped, and the model's material was re-created to incorporate the flag.  The model was then taken back into Carrara where wave modifiers were applied to the flag to give it an appearance of being in the wind.



Packing the UVs Inside the Template

Once all of the parts have been mapped, it is time to move them all into the UV working space, and arrange their sizes and positions to make the most efficient use of the available texture area.  The working space is the white box in the UV Editor window.

Usually, you never want to let the positions of the individual maps overlap, so that each part of the model will have its own unique texture.  However, this model had a great many parts, so texture overlapping was permitted in the parts with similar textures.  Offsetting the positions of the different groups introduces an element of randomness, and keeps the different textures from looking like clones. 

The UVs for the different groups were scaled and arranged in areas of the map as shown below.  When the arrangement was complete, the UV Map was exported and used in Photoshop as a template for making the color and bump texture maps.




  The texture map for the color channel is shown below.  The top quarter of the map is used for the sails and the flag.  The next quarter is split between the light wood texture on the left for the wooden railings, and the rope texture on the right.  The third quarter is for the darker wood used in the ship's keel, masts, and support beams.  The bottom quarter is made up of a plank texture used for the body of the ship.  The wood and rope textures, which came from 3dStudio.com, were tiled to fill out their respective areas in the texture map.




  The texture map for the bump channel shown below, is a grayscale version of the color map, except for the sails which have faint creases added to show the sections of the sails that have been stitched together.




  A parting shot of the finished model is shown below.  This image, and the image at the start of the tutorial were rendered in Carrara Studio 3.






Copyright © 2004, Carl E Schou, All Rights Reserved