In my previous post on 'Setting Up in the Real World' I showed an example of zig-zag edges on my sample model located in the Shetland Islands incorrectly attributing this glitch to the model's distance from the Design File Origin:
On closer inspection it turns out that an excessive distance was involved, but not that between this part of the model and the file origin.
In addition to this trivial test model some other elements exist several hundred km away near the Design File Origin. The issue is with the display depths, when front/back clipping is off (which is typical) we try to dynamically compute the front/back planes based on the entire model extents. In this case the overlooked elements result in a huge display volume being calculated when the camera is off. The z-extents of the view in parallel projection are then too great affecting the resolution. The position of the viewpoint 276km away from the part of the model I'm actually looking at is determined by the computed view extents:
In Wireframe this could pass unnoticed, but as soon as a shaded mode is applied the zig-zags appear.
Using the Define Camera tool the unexpected coordinates of the viewpoint/camera can be seen both in the Tool Settings Dialog and graphically when Display View Cone is ticked On:
Working units are metres, so you can see that the Camera Eye Point and Target are only a few metres apart but both are about 276km away from the model!
Use the Setup Camera tool to define a Camera View by Eye Point and Target near the model and the view frustrum is clipped with a much more appropriate range so resolution is normal and zig-zags do not occur.
Reverting to a parallel projection view takes us back to calculated clip planes so the error recurs. In this case cleaning up the model will reduce the overall z-extents removing the problem. Setting the front and back clipping planes to restrict the active Z extents is another solution but cleaning up your data is always the best option in the long term.
Use the Display Active Depth tool to show the current Active Depth in the Status bar:
Despite the large numbers the actual display depth shown here is only about 37m.
To change the Active Depth use the Set Display Depth tool.
Both can be found in the View tools or added to the View control tools displayed in each window's View Toolbox.