Locking out a region with Ground Control
The Lock design option on a Ground Control polygon lets you freeze an area of the site to your current proposed surface. Level AI then preserves that area exactly as it is on the proposed surface instead of regrading it.
This is useful when you want to protect a region you have already designed, for example:
A hand-graded pad or an already-approved area
Grading taken directly from your road corridors
Any area that must not change between runs
⚠️ Prerequisite — you must have a proposed surface selected.
Locking out an area locks it to the project's proposed surface, so one must be selected before you run Level AI Prepare. This can be either:
An Allsite proposed surface, or
A Civil 3D corridor surface (e.g. the "Top" surface from your road corridors)
If no proposed surface is selected — or it cannot be found in the drawing — Level AI Prepare will stop with an error.
Step 1 – Select your proposed surface
Choose the surface that Level AI will lock the area to. This can be either an Allsite proposed surface or a corridor surface.
Make sure the surface is built. Level AI Prepare will automatically rebuild it if it is out of date, but it must exist in the drawing.
Step 2 – Draw the Ground Control polygon
Select Grading → Ground Control and draw a polygon around the region you want to lock out.
Step 3 – Turn on Lock design
On the Ground Control polygon, set Lock design to on. When enabled, the area is locked to the current model surface (roads and feature lines) — Level AI keeps this region fixed rather than regrading it.
You can still use other Ground Control areas (without Lock design) elsewhere on the site to constrain grade, elevation, cut/fill, etc.
Step 4 – Run Level AI Prepare
Run Level AI Prepare to validate the drawing. Because a locked area is present, Prepare will:
Confirm the selected proposed surface exists in the drawing
Rebuild that surface if it is out of date
If no proposed surface is selected or it cannot be found, Prepare stops with a validation error — return to Step 1 and select a valid surface.
Step 5 – Run Level AI
Run Level AI. The locked region keeps the grading from your selected proposed (or corridor) surface, while the rest of the site is graded normally by Level AI.
Related
Ground Control / Impervious — all Ground Control polygon settings