Civil 3D parcels are used by Level AI to define residential lots, drainage areas, parks and other graded areas.
When a DWG is converted to Allsite any existing Civil 3D parcels get Allsite extended data automatically applied, this includes lot grade information and other data for both Service AI and Level AI to run. However, each parcel still needs to be classified so Level AI knows how it should be graded.
Before running Level AI
Complete these two main steps:
1. Configure the default parcel settings on the web. These settings control the default lot grades, drainage behaviour, protective slopes, driveway grades and yard grades. (See section below)
2. Assign parcel categories in Civil 3D. This is a minimum requirement for a Level AI run. At least 10% of the parcels must be assigned the NORMAL category. (See section below)
For a typical residential project:
Set residential parcels to NORMAL.
Set their Normal Parcel Sub Type to SINGLE FAMILY, where applicable.
Use the appropriate categories for non-residential parcels, such as PUBLIC DRAINAGE for parcels containing detention or retention ponds.
Review any parcels without a category before running the final model.
Sometimes tiny parcels are automatically created in road corridors. Use the Toolspace to find and remove these.
1. Default parcel settings (configured in the web)
Before working with Civil 3D parcels in Allsite, it is first necessary to configure the project settings on the web. These settings define the default grading behaviour and must be in place before any model is run.
When parcels are converted to Allsite on Civil 3D, they do not have any settings configured automatically.
Once a parcel category has been assigned, Level AI applies the default lot settings from the linked Allsite.ai project. You can review these settings on the web or by selecting Settings from the Allsite ribbon in Civil 3D.
The project settings control initial grading values and behaviour, including:
Minimum and maximum lot grades
Lot grading typology
Protective slopes
Driveway grades
Front, side and rear yard grades
These settings define the initial values for things such as parcel lot grades and lot typology. See below for more information on different Normal lot sub types. They also define the behaviour of the lot system to grades, such as protective slopes, driveway and rear yard grades.
Default grades
This table define the lot typology and grades for different lot category. See here for more details on lot typology.
Setting | Description |
Default minimum grade (%) | Project-wide default absolute minimum (drainage) grade applied to all lots / areas unless overridden per parcel (see Min/Max Grade under Parcel Settings). Default 0.5%. |
Default maximum grade (%) | Project-wide default absolute maximum grade applied to all lots / areas unless overridden per parcel. Default 33%. |
Protective Slopes
This defines the graded surface immediately surrounding a building platform, designed to direct runoff away from the building and out of the lot. Feature lines are automatically added defining the shape of the flow lines / swales. These are only relevant for single family NORMAL lot typology when a building is on the parcel.
Protective slope feature lines can be disabled or partially disabled in the output surface — see Surface Feature Lines below.
Protective slopes are only effective when the protective slope distance is such that the protective slope intersects with the edge of the parcel (ie flow line). If the distance does not reach the parcel edge the protective slope is still generated, but will not be effective.
To disable protective slopes for a single building, set the protective slope distance on that individual building to zero.
Setting | Description |
Flow line slope comfort (%) Flow line min / max grade (%)
| Target and limits for grades of the swale / flow line collecting run-off from the building and taking it out of the site. |
Protective slope min / max grade (%) | Minimum and maximum limits of the protective slope around building. |
Protective slope distance | Distance away from building the protective slope connects with the flow line. |
Driveway Grades
This defines the graded surface at the front NORMAL category, SINGLE FAMILY type lots. See detailed grading below for details.
Setting | Description |
Driveway max grade initial (%) | Maximum grade of the first 6.5ft of the parcel |
Driveway transition max grade change (%) | Maximum grade of the subsequent 6.5ft of the parcel |
Driveway max grade (%) | Applied to impervious DRIVEWAY type. Note, if driveways set to auto generate (refer to Layout Assist settings) this grade is applied to the driveway. |
Front/Side/Rear Yard
This defines the graded surface at the front, side and rear of NORMAL type lots. See detailed grading below for details.
Setting | Description |
Front/Side/Rear yard max slope (%) | Maximum grade of the front / side / rear yard |
Front/Side/Rear yard setback | Distance from front / side / rear of lot to apply the rear yard max slope. Also used to help place buildings for Layout Assist. |
Surface Feature Lines
Setting | Description |
Protective slope feature lines | For non-vacant lots, the locations for protective slopes (and flow lines) around the building. Can be:
Default "All" protective slope lines output. Only applies to lots with buildings that are NORMAL category and SINGLE FAMILY sub type. |
Draw vacant lot setback feature line | For vacant lots, draws a feature line at the front, rear and side setbacks provided above. This helps to provide the grade definition within surface triangulation for the given areas of the site. If using Vehicle Crossing Relationships it can be useful to enable this setting (so grade to VC can be seen in the surface).
By default no setback feature lines are output. Only applies to vacant lots with NORMAL category and SINGLE FAMILY sub type. |
Draw building FFL feature line | The locations for protective slopes (and flow lines) around the building. Can be:
|
NOTE:
Protective slope feature lines are output on all lots that are set to NORMAL category and SINGLE FAMILY sub-type. This includes corner lots and lots with retaining walls.
2. Assign parcel settings in Civil 3D
Once the parcel has its Allsite extended data automatically added you can customise settings on a per parcel basis.
As all parcels are automatically assigned default category on creation (to "NORMAL" category defined in default settings), remember to change any category for PUBLIC DRAINAGE or PUBLIC PARK parcels that are not residential (ie small end parcels or parcels with detention ponds.)
Setting | Description |
Category | This defines the category of a lot. All lots need a category and the category will determine how Level AI applies grading.
NORMAL category lots can have further refinement of their grading - see 'Normal Parcel Type'.
PUBLIC DRAINAGE lot category will not have Storm / sanitary connections. Use for lots that have detention/retention in them.
PUBLIC PARK lot category does not have Storm / sanitary connections
SUPERLOT - this can be used for parcels that will be cut up later into NORMAL category lots. Superlots are ignored by Level AI (ie can overlap other parcels)
You don't need to set a PUBLIC ROAD parcel as this will automatically be created based on the road corridor. Public road parcels will have grading consistent with the crossfall of the road including daylight settings from your Assembly.
NOTE - At least 10% of parcels need to be of NORMAL category. Review comments will be added on any parcels with no category including areas where there is no parcel defined. |
Normal Parcel Sub Type | Only relevant to NORMAL category parcels. This tells Level AI the way the lot will grade. If set to 'Single Family' it will automatically determine whether lot will be Type A, B or C.
If no building on the lot set to one of the VACANT lot sub types. |
Min/Max Grade | Sets the grade tolerance for the parcel. Note - if parcel has a building on it then other grade parameters from the web Lot settings will additionally define grade on parts of the lot (building protective slope, front, rear, side lot grades) |
Max Cut / Fill | Define the maximum amount of cut or fill allowed for the parcel. You can set a negative value (for example a -1 foot cut on the site will mean at least 1 foot of fill used on the parcel). Common uses for this are: - Prevent excavation of ground with potential artifacts. - Avoid cutting where there is existing underground infrastructure (ie an underground gas pipe) |
Drain to road | If enabled, will ensure the polygon grades to the closest road. |
Min / Max Elevation | Allow you to specify a parcel to be above a certain elevation. Some common uses for this are: - to keep out of a flood zone - to ensure parcel is elevated for views. |
Smooth | If enabled, smooths the area (ie forces it to be graded), if disabled, will only touch the ground to meet grading controls. |
Vehicle Crossing / Driveway Placement (width, location) | Configure the location of vehicle crossing (determines where potential grade breaks will be placed at the road frontage of the parcel). Location specified as High, Mid, Low - this looks at the existing surface (initial run) or the last design surface to determine location of vehicle crossing. Defaults to middle of road frontage. |
Services Connection and offset | For use with Service AI to say where it is preferrable to connect services into the parcel. If parcel should not have a connection, set to "NOT CONNECTED"
NORMAL parcels will apply the default storm / waste connection (from web) if left unset. |
Services Placement and offset | For use with Service AI to say where service lines should run within a parcel. For example if Sanitary pipes are preferred to run down the rear of a parcel, offset by 6 feet, then would set "Sanitary Placement" to REAR and "Sanitary Offset" to 6 ft. |
Subnetworks | For use with Service AI, defines the subnetwork for the storm / sanitary. If set to blank will be automatically set to subnetwork 1 if there is a respective service connection. |
Relationships (fall to vehicle crossing) | Relationship between the pad location (ie centre of parcel) and the vehicle crossing, specified as a Min, a Max, or just one of the two. This controls the elevation of the pad relative to the road at the point of vehicle crossing — most commonly to hold the pad above the road by a set amount, but negative values can be used to hold it below the road.
Applies to vacant parcels only. See Vehicle Crossing Relationships below for the sign convention, one-sided values, worked examples, and what to use instead on a lot with a building. |
Protective slope distance and grade can also be overridden on the individual building (not the parcel), overriding the project / web defaults for that building — see Protective Slopes above. Leave blank to inherit the project defaults; set the distance to zero to disable the protective slope for that building.
Vehicle Crossing Relationships
A vehicle crossing (VC) relationship holds a vacant parcel's pad area at a controlled elevation difference from the road at the vehicle crossing. It is set per parcel as a Min and a Max, or just one of the two (the Relationships (fall to vehicle crossing) setting above), and it is the only relationship type that targets the vehicle crossing location itself.
Vacant parcels only. The relationship is applied between the vehicle crossing and the vacant lot's pseudo 'pad' area (the area left inside the front, rear and side setbacks — see Vacant Parcels below).
Once a building is placed on the lot there is no pseudo pad for the relationship to attach to, and the fall-to-VC values are not applied. Use a grading relationship on the building instead.
Which relationship type to use
Lot | Use |
Vacant lot — hold the pad relative to the road at the vehicle crossing | The Vehicle crossing min/max relationship on the parcel (set Min and/or Max fall to VC).
This is the only way to constrain against the vehicle crossing location. |
Lot with a building — hold the building relative to the road | A Grading Relationship on the building, to a road modifier (curb), road centerline, road centerpoint or corridor extent — or to another building.
Note this ties the building to the point it is snapped to on that road feature, not to the vehicle crossing location. |
Sign convention (including negative relationships)
Min and Max are signed elevation differences of the pad relative to the road at the vehicle crossing:
Positive — pad sits above the road
Negative — pad sits below the road (for example a walkout or lookout lot, or a lot falling away from the road)
Min must always be the lower (more negative) value and Max the higher value. Because the values are signed rather than magnitudes, for a pad below the road the Min is the deeper of the two figures.
Either value can be left blank to constrain one side only. A Min on its own holds the pad no lower than that difference and leaves it free above; a Max on its own holds it no higher and leaves it free below. A one-sided relationship is often easier to satisfy on a lot that is already tightly constrained by other controls.
Requirement | Min VC relationship | Max VC relationship |
Pad between 1 ft and 2 ft above the road | 1 ft | 2 ft |
Pad at least 1 ft above the road, no upper limit | 1 ft | leave blank |
Pad no more than 3 ft above the road, no lower limit | leave blank | 3 ft |
Pad between 1.5 ft and 3 ft below the road | -3 ft | -1.5 ft |
Pad level with the road or up to 2 ft below it | -2 ft | 0 ft |
A common mistake on a below-road parcel is to enter the figures in the order they are spoken — "1.5 ft to 3 ft below" as Min -1.5 ft / Max -3 ft. That is an inverted range (Min higher than Max) and will not give the intended constraint. Enter Min -3 ft and Max -1.5 ft.
Level AI Prepare will detect a reversed range, swap the two values and note the correction in the run log.
Also worth knowing when working with VC relationships:
Enable Draw vacant lot setback feature line (see Surface Feature Lines) so the grade to the vehicle crossing can be seen in the output surface.
Like any relationship, a VC relationship can cause runaway or non-viability if the range fights other controls on the lot — parcel min/max grade, max cut/fill, min/max elevation, or the driveway and yard grades. Keep the Min to Max window wide enough for Level AI to iterate, or constrain one side only.
If a lot ends up with no vehicle crossing at all (for example its only frontage runs along a retaining wall), the fall-to-VC relationship has nothing to terminate at and is ignored for that run. A review comment is added against the lot — add an impervious DRIVEWAY feature to locate the crossing explicitly.
Normal Category Lot Typology
Three different 'NORMAL category' typologies are supported for Single Family residential.
Type A - Drain to road
Type B - Split, front drains to road, back drains out back
Type C - Drain to rear
If the lot sub type is set to SINGLE FAMILY it automatically determines the type based on other grading parameters.
Flow around the building is controlled by protective slope breaklines and swale breaklines, which channel the surface either towards the road (Type A), towards the rear (Type C), or split between the two (Type B).
Single family lots have the additional grading features where building 'protective slopes' are automatically added around the house, this ensures correct drainage.
Settings for protective slopes are described above.
More details of protective slope and lot typology:
Detailed Parcel Grading
For NORMAL category, SINGLE FAMILY type lots you can specify setbacks for side, rear and front of lot. Each area of the lot can have different grading characteristics, these are different if it is a Vacant vs Non Vacant parcel.
Vacant Parcels
For Vacant parcels, the building setbacks form a pseudo 'pad' area. This is the area remaining after the front, rear and side yard setbacks have been created. This will have a breakline in the resulting Level AI model. Note - the 'pad' area is still set with a max grade the same as that of the parcel. If you want an actual pad (ie flat area) add a building.
This pseudo 'pad' area is what a vehicle crossing relationship controls, which is why that relationship applies to vacant parcels only.
Non Vacant Parcels
When a building is placed on the lot and the type is set to SINGLE FAMILY a protective slope is added (see above for protective slope grade and size settings). The front and rear yard grades will have priority over the protective slope grade, but the protective slope has priority over the side yard slope. The remaining areas are graded as per max lot grading. Note - if the side, rear and front max grades are left blank it will just inherit the lots max grade.
Break lines are added for the protective slope and building pad.
Reviewing Parcel Max Grades
Within Civil 3D, after a Level AI run you can view the parcel areas and the SINGLE FAMILY parcel max grading.
Hover over the area to see the classification and the max grade for the area.
