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## Restricting the number of labels

Most computational meshes contain many thousands, millions, or even billions of nodes and cells. Adding that many labels would quickly become burdensome on the computer and would result in a Label plot so dense that individual labels could no longer be read or even associated with their cell or node.

VisIt's Label plot restricts the number of labels by default to some user-settable number of labels that can comfortably fit on the screen. The method used to restrict the number of labels differs for 2D and 3D plots. For 2D plots, the viewable portion of world space is periodically subdivided, based on the zoom level, into some number of bins to which labels are then assigned. As you zoom in on the Label plot, labels that go beyond the viewport are no longer drawn and new labels that were previously hidden take their place. This allows the Label plot to efficiently draw many labels without crowding the labels on top of each other. For 3D plots, the Label plot divides up the screen into a user-settable number of bins. All label coordinates are transformed so that they can be assigned to a screen bin and the label wins the screen bin if it is closer than the label that was previously in the bin. This ensures that a small subset of all possible labels is drawn and that they do not usually overlap on the screen. If you find that the labels appear to be from the back of the mesh instead of from the front, it's quite possible that the normals generated for your mesh were inverted for some reason. To combat this problem, select Back or Front or Back from the Draw labels that face combo box.

If you want to set the number of labels that the Label plot will draw, you can type in a new value into the spin box next to the Restrict number of labels to check box or use the up and down arrows on the spin box. If you want to force the Label plot to draw all labels, you can turn off the Restrict number of labels to check box. Sometimes making the Label plot draw all of the labels can be faster than drawing a subset of labels.