Sometimes the arrows head Civil 3D provides doesn’t encompass all of the options we want. If you try to add a custom arrow head to a Surface Slope arrow with an expression added to always have it point downhill you may find that it doesn’t rotate the way it should. This appears to be due to the Direction Arrow not flipping, but just the arrow head (the start stays the start and the end stays the end, but the arrow head goes from the start to the end instead of rotating both the line and the arrow).
We can use an additional expression to fix this. The expression will adjust the X offset for the arrow head. In this example the length of arrow is based on the picked points. If you want a fixed length arrow you’ll have to adjust the expression to match the length of the line. The expression is rather simple, just see if the arrow head needs to be offset and if it does adjust it by the picked points length:
I called the expression ArrowheadOffset. Then we can add the offset to the label style.
Once we close out of the label style composer we can see that the arrowhead is now in the correct location and rotation.
I think I may have skipped some steps but you can download the the completed style from this link: http://style.civil3dreminders.com/Slope_arrow_test-Fixed.dwg The file is in Civil 3D 2010 format.
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