Visualizing vector data by arrows

Arrows are usually used to visualize vector data. The magnitude of the data is represented by their lengths, and the direction of the data by arrow-head directions. In case of 3-dimensional solid analysis, arrows may be rendered as 3-dimensional solid objects. The following figure shows an example of ground water flow analysis, in which the flow directions are represented by arrows. In this example, an arrow indicates only the direction of the flow at the point, but not magnitude. So, the arrow length has no significance.

< Ground water flow directions represented by arrows >

> Setting the arrow display options

In oder to get arrow image of a vector data set, first select "Vector..." items from menu. Then, "Arrow Display" dialog appears on the screen as shown in the following figure. There are a number of items in this dialog. Each item has default setting. Change the setting if necessary. Click button if every item is set as desired. Then, the arrow image will be displayed.

<"Vector Display" dialog >

> Selecting the data item

The popup menu in "Vector Display" dialog has the list of data items which can be displayed by arrow representation. One of the items should be selected from this popup menu. The data associated with the currently selected popup menu item is displayed by arrow image. The first item is always selected initially when the "Arrow Display" dialog is first opened. But the item used for the last arro w display will be selected automatically when the dialog is opened next. The popup menu items vary depending on the analysis type. Only those output items appropriate for vector display appear on the popup menu. They are shown below. Not all the items are always shown in the popup menu. If you exclude any of the output items in "Analysis Options" dialog described in Chapter 6, the corresponding item(s) will not be shown. If you are using an external solver, the menu items may be different from those shown below, because the popup menu items can be customized by the external solvers.

< Popup menu selecting the arrow display data item >

> Selecting the type of arrow rendering

Arrows may be rendered in 3 different types. Select one of the types by turning on the corresponding radio button. 

> Selecting the style of surface or boundary surface rendering

The arrows are usually rendered together with the surfaces on which the arrows lie, or the boundary surfaces of the volumes containing the arrows. Select the style of the surface rendering by turning on one of the following radio buttons in "Vector Display" dialog:

< Type of arrow and boundary surface rendering>

> Setting the placement focus of arrows

An arrow may be placed at various positions relative to its data point. The placement focus of an arrow implies the position of the arrow, which matches with the data point, and can be set as one of the following options: 

< Arrow placement >

> Setting the position of arrow heads

An arrow can be drawn either with or without arrow head. At the same time, the arrow head may be attached at the starting point or the ending point of the arrow. Thus, there are the following 3 options related to arrow heads:  

> Setting the length of arrows

The length of an arrow may or may not represent the magnitude of its corresponding data value, depending on whether the corresponding vector data have magnitude or not. For example, displacements in structural analysis have magnitudes as well as directions. But, there are such vector data as principal stress directions for example, in which the data has only direction, not magnitude. In either case, the length of the arrow is determined on the basis of the predefined length factor. The length factor is defined by entering its value in the editable text box labeled "Length" in the dialog. The entered value should be greater than 0, and represents a factor determining the arrow length. The length is independent of the view scale of the model. Thus, the length of arrow remains unchanged even if the screen scale is altered.

< Length and thickness of arrow >

> Setting the thickness of arrows

This item is effective only for "Solid arrow in 3-D volume" option. The length of the arrow rendered as 3-D solid is determined on the basis of the predefined thickness factor. The thickness factor is defined by entering its value in the editable text box labeled "Thickness" in the dialog. The entered value should be greater than 0, and represents a factor determining the arrow thickness. The thickness is independent of the view scale of the model. Thus, the thickness of arrow remains unchanged even if the screen scale is altered.

> Displaying selectively sampled arrows

One arrow is usually displayed at every data point, which may be a node or a point in an element. As the model becomes complex, the number of data points increases. Sometimes, there are too many arrows crowded around a point to visualize the data properly. Such complexity in visualization can be alleviated by displaying the arrows partially. The proportion of arrows for selective display is designated by the value entered in in the editable text box labeled "Sampling out of" in the dialog. If the value is 1, one arrow is displayed at every data point. In other words, all the arrows will be displayed. If it is 5 for example, arrows are displayed only at one out of 5 data points.

> Overlaying vector images

It is sometimes necessary to overlay two or more vector images. For example, the directions of two principal stresses, s1 and s2, are desired to be displayed together in order to improve the visual understanding of the computed results. In this case, the directions of s1 are first drawn, and those of s2 are overlaid over the existing image. Such overlaying vector images can easily be achieved by using "None" option for surface rendering. This option adds the new vector image over the previously drawn image.

< Displaying selectively sampled arrows >

< Overlaying vector images >