Overlapped polygons may introduce ambiguity in electrical simulation. They will not be considered as electrically connected if they are not specially treated. Please keep in mind that polygons are considered electrically connected on IE3D only when they have common edges. Many mechanical oriented layout editors do not have the same electrical connection concept as IE3D. Many technicians draw a geometry as it looks like what they want. They may not care whether it is meaningful and whether it contains enough geometry information. For example, a technician may draw a polygon as multiple isolated line segments.
The isolated line segments may look like they form a polygon. However, they are still considered as some line segments on IE3D and most layout editors.
We have implemented strong capability on the IE3D to handle overlapped polygons. The IE3D engine can automatically clean overlapped polygons in case they are any. However, such cleaning is automatically done and it may not be what you want. It would be nice you can clean them before you start a simulation. In this section, we will demonstrate how we handle overlapped polygons on MGRID.
Step 1 Select File->Open command and select file .\ie3d\samples\overlap.geo. The structure is opened on MGRID with a warning message “Overlapped Polygons Detected” (see Figure 4.5).
Polygon 2 and polygon 3 shown in Figure 4.6 are overlapped.
The dialog “Overlapped Polygons Detected” may appear quite frequently when you are doing editing. You have 5 options in such a case. The different options are discussed in Table 4.1.
Step 2 Select Highlight Them button in Figure 4.5. MGRID will show the opened structure. However, MGRID will show the polygons 2 and 3 in Figure 4.6 with pink color instead of the color for polygon 1 even the three polygons are on the same layer. The pink color indicates that the polygons 2 and 3 are overlapping with each other.
4-4 Figure 4.5 The Overlapped Polygons Detected dialog.
Table 4.1 The options for the Overlapped Polygons Detected dialog.
Option Description
Clean Them MGRID will try to cut the overlapped polygons to make sure they will not be overlapping each other.
Select Them MGRID will get into Edit->Select Polygon mode and select the overlapped polygons.
Highlight Them MGRID will not change anything. However, it will highlight the overlapped polygons.
No Action MGRID will do nothing and it will not highlight the overlapped polygons.
Cancel If MGRID detects the overlapped polygons after an editing command and you choose Cancel, MGRID will undo the change of the editing command. If it is opening a file, it will be like No Action.
Figure 4.5 The “Overlapped Polygons Detected” dialog.
Figure 4.6 overlapped polygons in .\ie3d\samples\overlap.geo.
Step 3 Select Adv Edit->Overlapped, Multi-Looped and Twisted Polygons->Cut Overlapped Polygons command. MGRID will prompt you the Cut Overlapped Polygons dialog (see Figure 4.7). There are different options there. The list box for the Cutting Option is disabled. It is only highlighted if you select the command after you select some polygons. There are options for
“After Cutting Process” for you. You can choose to merge the polygons after the cutting process.
You can also choose to remove redundant vertices on curvature. For this option, MGRID may change the shape of curved structure slightly with some vertices removed. The “Remove
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Redundant Vertices on Curvatures” is a command in the Adv. Edit menu. We will discuss about it later in this manual.
Figure 4.7 The Cut Overlapped Polygons dialog.
(a) The connected polygons after Step 4 (b) The connected polygons after cutting if you Select the polygon 2 before the command.
Figure 4.8 The results of cutting overlapped polygons with different options.
Step 4 Select OK and MGRID will cut the overlapped polygons. You will see a red dot between the polygons 2 and 3 after the cutting, meaning the two polygons are connected after the connecting (see Figure 4.8a). If you select Adv Edit-> Overlapped, Multi-Looped and Twisted Polygons Check Polygon Overlapping command, MGRID will inform you that no overlapped polygons are detected.
In case you select the polygon 2 before you select Cut Overlapped Polygons command. The Cutting Option list box will be highlighted. If you select “Cut all overlapped polygons with selected polygons unchanged” in the Cutting Option, you will get the result in Figure 4.8b.
General speaking, the connection in Figure 4.8b is not as good as the one in Figure 4.8a. We just want to show you some feature you may possibly need in building geometry on the MGRID. We may need this kind of flexibility occasionally.
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We have demonstrated how we can detect and clean overlapped polygons in the above examples. However, please keep in mind the commands we used and the automatic detection are only good for 2D polygons only. They do not apply to 3D overlapped polygons. The reason for it is that 3D overlapped polygons are much more difficult to detect and cleaned. The process may take a long time when the number of polygons is big. In IE3D 14, we have implemented a command to clean 3D overlapped polygons.
Step 5 Open file .\ie3d\samples\overlap_3d.geo. You can see there are three 2D (or horizontal) polygons. There is one 3D polygon spanning between z = 0 and z = 22 connecting between the bottom and top grounds. There are some red dots on two edges lying on the bottom and top ground planes. The red dots denote the polygons are connecting to both the bottom and top ground planes. On IE3D, when an edge of a 3D polygon is lying on an infinite ground plane, it means that the polygon is connected to the infinite ground.
Figure 4.9 The top view and the 3D view of the overlap_3d.geo file.
When you open the file, MGRID does not complain about the overlapped polygons. This is normally because the Check Overlapped Polygons command only considers the case with 2D polygons overlapping with 2D polygons. For this case, the 2D polygon and the 3D polygon are overlapping and this overlapping is transparent to the command.
If you have 2 metallic strips crossing each other in your design, they are electrically connected.
For the above IE3D model, it is not a correct model because it may not consider the polygons are connected. If you simulate it as it is, it may not be able to yield accurate results. How can we fix the structure?
Step 6 Select Adv Edit->Connection->Adjust Geometry for Connection. MGRID will prompt you a dialog. Please select OK and MGRID will cut the 2 polygons and connect them for you. The results are saved in: .\ie3d\samples\connect_3d.geo. For this structure, the 3D polygon is electrically connected to the 2D polygon and it is also connected to the bottom and top ground planes.
The Adjust Geometry for Connection is an old command on MGRID. However, the feature to divide overlapped 3D polygons is a new feature implemented in IE3D 14. It is not automatically called in the geometry modeling at this time considering the fact this is a very sophisticated command. It may take a long time and it may need more time to make sure it is robust enough so that we can integrate it into the geometry modeling routine. To make sure 3D overlapped
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polygons are electrically connected, you do need to select this command from time to time. Also, please check the results. Again, it is a new command. We can’t be sure the results are 100%
reliable. Table 4.2 summarizes the different situations in overlapping detection and cleaning.
Figure 4.10 Polygons are divided to create matching edges for connections.
Table 4.2 The different situations of polygons overlapping
Case Detection Cleaning
You can select Clean button to let MGRID divide the polygons for connection for you automatically. You can also select Cut Overlapped Polygons command to clean them. Geometry for Connections command on MGRID 14 or later versions to clean them.