Hi Aaron. I did a search of the forums for what I was looking for, but all the posts are from almost 3 or 4 years ago, so I was hoping to bring this back onto the radar (note: I just read through the Dev Plans (for v3.0 and unscheduled features), but I'm not sure if all of the concepts that I am going to suggest are covered by those documents).
Due to the fact that I am using L3DT in a limited manner (only modifying real-world heighfields), there may be some techniques that I am unaware of (that come from the design process). I have read up a little on the masks functionality, and was wondering if it would be applicable at all to heighfields. Coming from the VBS2 world, there is the ability within the terrain editing software (Visitor4 (V4)) to use SHAPEfiles (either imported or created within the software) to modify the vertices that are under them. Would that be possible within L3DT (using vector files)??? If not, the other idea I had was to export the SHAPEfiles as images (either via GM or the built in ability of V4), be they PNG, BMP, etc, and use those as a mask that would allow the area within the "mask" to be locked, or an inverse-selection mode (i.e lock everything outside of the mask). I am guessing that, ATM, it isn't possible to do this.... if it is, I will immediately plant a tree in your honour!! Otherwise, I will wait anxiously for this ability to be implemented.
One of the things, for real world map creation, that is critical is too ensure that one doesn't alter the terrain too much. Depending on the resolution of the data that you receive, the area created by this data is only somewhat close to the real world ("good from far, far from good"), and a certain amount of carving, sculpting, etc are required to make the area more realistic, but one has to be mindful of how much "virtual dirt" is excavated. To that end, would it be possible to apply a given range to a brush. Something along the lines of Lower To, but a relative distance, versus and absolute distance. So, "Raise XX meters", or "Lower YY meters"??
Another thing that I just thought of that would be excellent for creating nice rivers, valleys, etc, would be an ability to adjust the base of the brush (like in Cliffs where there is a top and bottom circle) to be smaller (like a funnel), so that when a brush is applied more area is removed, and at the bottom, less.
As well, I saw it mentioned somewhere that a lasso selection would be a nice feature, and I agree. Another feature, which may not be feasible, but would make for some interesting terrain effects, would be a primitive-shape function: stars, triangles, ovals, rectangles (and perhaps a perfect circle/square functionality for the last two, by holding down a given key). I could see this used to create areas (and boolean abilities to add/subtract to/from selection areas would be nice), such as a series of long,thin ovals to create rolling hill effects (in conjunction with a gradient or fall-off effect).
Anyway, great work thus far, and I look forward to future releases of the software.