
	Polymesh Maps: Step 2: Extracting Maps

Figure 43 shows the map extraction controls in the Polymesh Maps window.

Figure 43. Map Controls

First set the output directory; click on the right arrow to the right of the Name label to bring up a directory selection window. Locate an existing directory, or type in the name of one to create, then hit the green Select button.

If you plan to create a VRML file, its important to select an empty directory for the maps and segmented polymesh to go into. If not, maps and polymeshes from other objects may be included in the final VRML file.

Next select the texture map format. If VRML output is planned, jpeg is best as the resulting image files are much smaller.

Now type the name of the segment, in this case armL for left arm, into the Name field. The resulting map will be called armL.jpeg, and the segmented polymesh will be saved into armL.ply.

You can now type the texture map dimensions into the X and Y fields, or click on the Map Size button to get CySlice to work out some reasonable values for you. Enable Pow 2 first if you want dimensions that are a power of 2; this can be important for some renderers.

Finally, the Mult field can be changed to globally scale all maps up or down by a constant factor.

Once all the map parameters have been set, click on the green Extract button to calculate the cylindrical texture map for all visible faces. It very important that you don't change the view from the "seam location" stage, described in the previous chapter, before extracting the map.

Figure 44. Arm Texture Map

Once the map is calculated, it will be displayed (see Figure 44).

Step 3: Polygon Reduction

Now its time to reduce the number of faces in the current segment. Use the <g> key to select the faces you want to decimate. The quickest way to select all visible faces is by the <g> <s> key sequence.

Figure 45. Decimate Controls

The number of selected faces will be shown next to the Num field in the decimate controls panel. You can then enter the reduced number of faces you want into the Num field, or type a percentage value less than 100 into the following % field. Be sure to hit <Enter> after typing either value, and the other field will update.

The Feature Weight is set at 50% by default. If you set this value to 100%, then areas of high curvature in the polymesh will be reduced much less than other parts of the mesh. Set this value to 0%, and the mesh will be more evenly reduced.

Figure 46. Selective Decimation

Most of a body scan can be reduced with the default feature weight of 50%. There is one exception though; if you want to retain detail in the eyes, ears, nose and lips, the head should reduced with a feature weight of 100%. There is also nothing stopping you from using the <g> key paint mode to select only some areas of the polymesh for decimation (see Figure 46).

Figure 47. Before and After Decimation

When you are ready to decimate the selected faces, simply hit the Reduce button. Once complete, you should Save the reduced visible faces into a PLY file, then View to see how it looks.

Step 4: Next Segment

Now void the faces that were just saved with the <v> <g> sequence, bring back the remaining hidden faces with <h> <u>, and restore the view with <Space-Home>.

You are now ready to go back to Step 1 to select and process the next segment. Make sure you:

(1)

Change the Name field.

(2)

Click on Map Size to recalculate the texture map dimension for the new segment.

(3)

Click on Extract to actually calculate the new texture map.

(4)

Check that the Feature Weight is appropriate for the geometry you are about to Reduce.

VRML Output

If you click on VRML Output, all segments in the output directory are collected together and converted into a single VRML file called out.wrl.

You can then edit this file if you wish to adjust the background color, initial viewing coordinates or rendering parameters.

For maximum download speed the WRL file should then be compressed with gzip. Rename the resulting compressed file so it has a WRZ extension, and you are ready then to copy that and the JPEG files onto your web server.