4.4.3.1. Optimizing 3D models when importing - Decimation

Object management in the program is slow if the face number of detailed 3D objects is so high that it adversely affects the computing and space load of the program. In most cases rendering quality will not decline with the significant decrease of face number. In such cases, it is preferable to work with the optimized object instead of the original one. Optimization is performed by an algorithm rejecting faces least affecting the shape, and the program will work with this algorithm speeding its operation.

Optimizing is allowed in the case of importing 3D Studio drawings and dwg/dxf format drawings containing 3D objects.

When importing 3D objects, the 3D Model Decimation dialog box will appear, where you can decide about the scale, i.e. scale factor (scaling rate), which defines the rate of decrease in the original face number.

&See the Chapter 4.4.3. 3DS Import.

A significant difference as regards the face limit you can set in Preferences (File - Preferences - General - 3D preferences menu) is that in the case of face limitation the amount of information concerning the model will not be reduced, whereas the scaling of the 3D model will cause the shrinking of information about the model.

In the 3D Model Decimation dialog box You can select any of the following three options:

• No decimation: the program will not optimize the model. You should select this option when working with simple objects, because this option keeps the original information content.

• Intervals: in the case of interval decimation, you can define the decimation rate in accordance with the original face number of the object.

• Simple: in the case of simple decimation, the program decimates the model with one rate, regardless of the original face number of the object.

Decimation with intervals

As a default, you can see those Max polygons, i.e. polygon number interval limits which the program will use. The program assesses the lowest Max polygon value, which exceeds or equals the polygon number of the imported 3D object. Decimation will be performed with the rate associated with this number. If none of the Max polygons satisfies this criterion, the program will use the decimation rate defined for Other. You can edit intervals as follows:

• If you want to edit an existing interval, double click on the Min polygons or the Ratio value and modify those values.

• If you want to delete an existing interval, click on the line of that interval then click Delete.

• If you want to add a new interval, first type in the polygon number value and decimation value in the corresponding entry fields then click on the New button.

• To reset default intervals, click on the Default button.

• Close the dialog box by clicking Ok to start decimation.

Simple decimation

Enter the Min polygons data. If the polygon number of the imported object is smaller than or equals this value, the program will not decimate during the import, regardless of the decimation value.

• Set the rate of Decimation. You can specify the exact value in the entry field or you can use the slide. In this case the program applies the rate of face number of the imported object estimated in terms of polygons.

• Click the Ok button to close the dialog box and to start decimation.

Example

The following imported model had 47672 faces before decimation:

If we exclude 75% of the faces, that is we specify a decimation rate of 0.25, the model in question will be simplified to a great extent, but at the same time computing will be easier and the shape of the model on the rendered picture will be equally visible.

• If You don’t use the decimation, the program hides the common edge of those neighboring triangles, which normal vector is the same. So unnecessary lines don’t cut up the surface of the object. The result appears in the vectorial 3D dialog window at hidden lines, or on the rendering picture. The disadvantage of the method is, that the object remains large.