Fundamentals: Masking a C3D Object

OK, so it’s not really a fundamental thing, but it falls in the “Oh, I thought everyone knew that,” category whenever I bring it up. And yet, lots of people don’t know. How to mask a portion of a C3D object, that doesn’t have a masking function? Read on….

So, you have an alignment referenced into your drawing. And for whatever reason, you need to hide part of it, say, the portion here inside my white polyline.


So, not easy to do. Unless you know that C3D is build on top of a bunch of old ADT tools, and that one of those is a masking tool. Type AECCONVERTLINEWORKTOMASKBLOCK at the command line, and select the closed poly. You’ll be presented with the following dialog:


You can choose to mask ALL AEC objects (like say, the surface underneath my alignment) or just specific ones. In this case, I just want the alignment to hide, so I’ll pick the options shown.

Pick the alignment, and voila:


The object is masked. I did go an modify the display style used by the mask object by clicking through and turning it off, but you could also have simply placed the linework on a no-plot layer if I understand it correctly.


  1. Jon Rizzo says:

    Or, knowing that Civil 3D is built on AutoCAD, you could draw a hatch using a plot style (or color) that has 0% screening.

  2. Jon Rizzo says:

    *sigh*. I just realized the silliness of my comment. Nothing to see here…these aren’t the droids you’re looking for…move along…

  3. Ray Fernandez says:

    Silly question:
    What is the advantage here, as opposed to the old WIPEOUT command, hiding frames, then using DRAWORDER to make sure the stationing is on top?

  4. As I understand it, this doesn’t mask anything but the object selected, regardless of draworder.

  5. sean twomey says:

    I couldn’t get this to work on the Surface Object (works great on everything else) – is there a trick to this?

  6. Jonathan Stewart says:

    The surface object has it’s own Masking found in the Prospector under the created surface. This is different then the a boundary because the triangulation of the surface still occurs under the Mask.

  7. sean twomey says:

    Ahhhhh (I can’t believe I didn’t realise this already)
    Now that I’m aware of this feature that’s been in the software possibly since it first came out, I may have a cunning use for it:)

  8. Jeff Paulsen says:

    I am not sure why you would mask a label but I did while I was randomly testing the mask on different objects.

    Be careful masking labels. I masked the EVC label portion of a vertical curve label and it changed the style for the visible parts of the VC label.

  9. Cynthia Colthorp says:

    I masked part of the line of a label in profile (to jog around other labels) and found it converted all text to standard as well (eventhough the default style for this drawing is set to ROMANS); is there a solution/fix? This was the first time I recognized a use for this type of masking as I still wanted to display the grid lines behind it and found it worked well, except for the aforementioned issue:(