Thursday, December 20, 2012

Which Way is North?

 Okay I admit it, the allure of one day being invited into the "Autodesk Expert Elite Program" has me checking the Autodesk Civil 3D Discussion Forums and blogging again. Since I'm only at the designated level of "Active Contributor", I have some work to do. Thanks, Autodesk!

The idea behind this post came from a question on the Autodesk Civil 3D Discussion Forums here. The issue is with a Civil 3D 2013 Dynamic North Arrow that is associated with a viewport with the UCS set to World, the dview twist angle set to "0", and the viewport set to plan. For some reason the north arrow was off by over 4.6 degrees. Bruce, a designated Autodesk "Expert Elite" himself, was kind enough to post a sample drawing to show the issue and here's what was discovered.:

Dynamic north arrows are associated with the 
selected coordinate system in the Units and Zone tab.

When you place a dynamic north arrow in a layout and associate it with a viewport, the block reads the current coordinate system that is assigned in the drawing settings Units and Zone tab and adjusts the default rotation of the block based on that setting. Even if there isn't a rotation in the viewport, the north arrow won't be pointing due north as you might expect. Here's an example.:

  1. In Civil 3D 2013, open an existing drawing or create a new drawing from scratch.
  2. On the model tab (modelspace) draw a rectangle of any size.
  3. In the Settings tab of Toolspace, right click on the drawing name and choose Edit Drawing Settings.
  4. On the Units and Zone tab, set the Drawing Settings Zone Categories to No Datum, No Projection.

    No Datum, No Projection

  5. In a layout (paperspace), create a rectangular viewport from scratch. Make sure you can see the rectangle in the viewport to verify rotation throughout this example. You may need to zoom out if necessary to see the rectangle rotation better.
  6. When you are in paperspace, there should be a Layout Tools ribbon tab available. Locate the Layout Elements Panel and select one of the built-in dynamic north arrows to place in the drawing.

    Select one of the built-in Dynamic North Arrows

  7. When prompted at the command line, select a viewport for the north arrow association.
  8. Next you'll be prompted to select a location to place the north arrow.
  9. The north arrow may be very small and hard to see. Set the x, y, and z scales to 20. Notice that it appears to be pointing due north when compare to the rectangle in the viewport.

    North is North
  10. To make sure we compare apples to apples, make a copy of the viewport in your drawing.
  11. Back in the Toolspace, Settings, Drawing Settings, Units and Zone tab, set the selected coordinate system to WA83-SF, then OK.
  12. Now place a new dynamic north arrow in the drawing using the second viewport (the copy) for the north arrow association. (Only one dynamic north arrow can be assigned to each viewport.)
  13. Place the second north arrow near the first one and again set the x, y, and z scales to 20.
  14. Notice that the north arrows don't point the same direction? That's because of the change made to the selected coordinate system.

    Compare the Dynamic North Arrows
This is definitely something that you need to take into consideration when you use the dynamic north arrows in a drawing with an assigned coordinate system other than No Datum, No Projection. If you do need to rotate the contents of a viewport, just set the coordinate system back to No Datum, No Projection before making the change, then reset the coordinate system as needed.

Another consideration is to set the coordinate system in the base drawing and attach it to a separate sheet drawing for plotting. The sheet doesn't need a coordinate system assigned to it so there won't be a discrepancy between plan north and the rotation of the dynamic north arrow.

UPDATE:  There is another solution that actually works better.

GEOGRAPHICLOCATION

In modelspace, type GEO at the command line then choose Remove the geographic location.



With the geographic location removed, you can keep the coordinate system assigned and the dynamic north arrow will point plan north as expected.

3 comments:

Bruce Klug said...

Tom,
Removing the Geo location just resets the zone to "no Datum...". After removing the geo information it appears to still have the zone set, but if you save, close, and re-open the drawing it gets reset to "no datum...".

Bruce Klug said...

Are there any workarounds that allow us to keep the datum info attached and NOT rotate the north arrow?

Tommie Richardson said...

Agreed. Not a perfect solution. Hopefully it'll get resolved in 2014 or with a service pack.

If you find this post and are experiencing this same issue, please submit a support request to Autodesk or post on the discussion forum to let your voice be heard.