Constraints & Rules

The LOP optimizer operates within a constraint system that reflects the physical realities of cargo loading. Constraints fall into two categories: hard constraints that can never be violated, and soft constraints that the optimizer tries to satisfy but will trade off against each other to find the best overall plan.

Understanding constraints helps you configure item properties correctly, interpret plan violations, and make informed decisions when manual editing.

Hard Constraints

Hard constraints are absolute rules. The optimizer never produces a placement that violates a hard constraint. If satisfying a hard constraint is impossible for a given item — because there is no space left, or the item is too heavy — the item remains unplaced.

After solving or making manual edits, click Validate to list the current constraint records (rule, message and container) in the score panel.

No Overlapping Items

No two items may occupy the same physical space. Every item's axis-aligned bounding box (AABB) must be completely non-overlapping with every other item's AABB.

This is the most fundamental geometric constraint. The optimizer uses collision detection on every candidate placement. During manual editing, dragging an item into a space occupied by another item is blocked — the item snaps to the nearest valid adjacent position.

Items Fully Inside Container Bounds

Every part of every item must be within the container's inner walls, floor, and ceiling. An item cannot protrude through a wall, floor, or roof panel.

Validate reports a hard door_passage violation for each placed item, pallet or rack whose placed width or height exceeds the container’s door width or height. A pallet or rack is checked as one composite body; STEP items use their placed bounding box. Equality passes: this is a nominal aperture check with no clearance margin, rotation search or transit simulation. The solver does not refuse the placement on this basis, and the check does not block manual placement.

Open-top, open-side and curtain-sided containers/trucks, and containers without a door, are not checked. Custom containers are checked against the door dimensions entered.

Total Weight Within Max Payload

The combined weight of all placed items must not exceed the container's maximum payload. The optimizer monitors cumulative weight in real time during the solving process and will leave items unplaced rather than exceed the payload limit.

In manual editing, adding or moving an item that pushes the total over the payload limit triggers an immediate violation flag on the payload metric.

Floor Load per Metre

Validate calculates the floor load per running metre: the cargo’s mass over any 1 m of the floor, measured along the container’s length. Each load reaches the floor through what it rests on. A pallet stands on its bottom boards when LOP knows its type’s board layout, and otherwise on its footprint; a loose item stands on its footprint. On the 20′ and 40′ general-purpose, high-cube, ventilated, pallet-wide and open-top containers, the result is compared with Hapag-Lloyd’s weight distribution guideline for a wooden floor: 4.8 t/m for 20′ and 3.0 t/m for 40′. Above the limit, Validate reports a hard line_load_exceeded violation; a load exactly at the limit passes. Other container types (45′, reefers, open-side, flat racks, tanks, road vehicles and ULDs) have no published figure in LOP and are not checked. As with door passage, the solver does not refuse a placement on this basis. These are calculations on the plan’s stated weights, not an inspection.

A custom container with its own floor rating (kg/m²) is checked against that rating: each item’s weight, plus everything standing on it, over its floor contact.

Orientation Locks Respected

If an item's orientation is set to This Side Up, only orientations that keep the item's designated top face pointing upward are considered during placement and manual rotation. The optimizer will never place a This Side Up item on its side or upside down.

Similarly, Vertical Only items are only placed standing upright, and Horizontal Only items are never placed standing on an end.

Hazmat Separation Distances

Items carrying hazmat separation tags must maintain minimum separation distances from other incompatible items. These distances are hard-coded compliance rules based on regulatory requirements:

If the container is too small to physically separate two incompatible items by the required distance, both items remain unplaced. The violation is reported with the specific tag combination and distance shortfall.

Nothing Stacked on Fragile Items

Items marked as Fragile cannot have any other items placed on top of them. The optimizer treats the top face of fragile items as unusable stacking surface.

If a fragile item is placed and then another item is manually dragged onto its top face, LOP immediately flags a hard constraint violation.

Stacking Weight and Crush Strength Limits

Two separate hard limits govern what may be stacked on an item, and they use different units:

• Max Weight on Top (kg) — the total cumulative weight of everything above the item. The optimizer sums the load above and rejects any placement that pushes it past the limit.
• Crush strength (kg/m²) — a pressure limit. The optimizer divides the load above by the item's top-face area and rejects placements where the resulting pressure exceeds the rating.

An item can carry either limit, both, or neither. Both are enforced during placement and re-checked on every validation.

During manual editing, adding items above a crush-sensitive item and exceeding its limit triggers an immediate violation.

A corrugated carton's compression estimate is a separate, soft calculation and never replaces either limit; see Carton compression (calculated).

Soft Constraints

Soft constraints are optimization targets. The optimizer tries to satisfy all of them, but when a perfect solution does not exist, it finds the best available trade-off. Violations of soft constraints reduce the relevant quality score but do not make a plan invalid or block export.

Center of Gravity Near Container Center

LOP calculates the cargo’s center of gravity (CoG) from the plan’s stated weights and compares its horizontal offset from the container’s middle with published guidance. These are validation thresholds:

The 5% and 10% follow the CTU Code (Annex 7, 3.1.4). An offset exactly at a limit passes. Validate prints the offset and both limits in metres (feet with imperial units) and says whether the CoG lies toward the door or the front wall. These are calculations on the plan’s stated weights, not an inspection.

Vertical CoG height is not checked — LOP does not evaluate how high the center of gravity sits, and no plan is validated against a vertical-CoG limit.

The CoG minimap at the bottom right of the viewport shows the load’s horizontal center of gravity relative to the container footprint. Its status uses the same limits: Centered within 5%, Acceptable where Validate gives a soft warning, and Off-center where it reports a hard violation.

Support Ratio ≥ 70%

Every item's bottom face should be at least 70% supported from below — either resting on the container floor, or resting on the top surface of items placed below it.

Items with a support ratio below 70% are at risk of tipping, rocking, or shifting during transport. The optimizer penalizes low support ratios in the Stability score. During manual editing, items with a support ratio warning are shown with an amber outline in the viewport.

Same-Group Items Placed Together

Items assigned to the same Group ID should be placed in adjacent positions. This is a soft clustering constraint: the optimizer scores higher plans that keep related items close together, making selective unloading and inventory management easier.

Group proximity is used for same-destination cargo, same-product batches, and kits that should stay together.

Heavy Items Below Light Items

The optimizer prefers arrangements where heavier items are lower in the container and lighter items are higher. This reflects good stacking practice: placing a 500 kg pallet on top of a 20 kg carton column would almost certainly exceed the carton's crush strength and create a stability hazard.

This is enforced as a soft preference to handle edge cases where geometry or other constraints make perfect weight layering impossible. The Stability and Damage Risk scores both reflect how well this principle is followed.

Viewing Violations in the Editor

During optimization: After the solver finishes, any items with constraint violations that could not be resolved are left unplaced and listed in the Unplaced Items section of the Items Panel with the reason they could not be placed.

After manual edits: Click Validate in the score panel.

• The score panel lists constraint records, with hard violations first and soft warnings after them. Each record shows its rule, message and container.
• In Smart Plan (Balanced) and Max Fill modes, the Space Utilization note shows the number of hard balance violations when that count is greater than zero.

Stacked pallet stability

Quick Plan, Smart Plan and Maximum Fill apply the same static pallet-pair rule and reject a pair that fails it. A level top is not required: contact area, stability and load-bearing capacity determine support.

The upper pallet’s center of gravity must stay at least 50 mm inside the convex hull of its contact area along both horizontal axes. A pallet bridging two stacks shares its load between supports using static balance. An item in a pallet below carries its own column plus the share of every pallet or loose unit standing on that pallet, each share split by static balance; a loose unit standing on a loaded pallet is checked for that load only. Racks are not judged as pallets in this rule; a rack standing on a loaded pallet counts as a loose unit.

Known bottom-board layouts are used when both the type code and platform match; GMA follows the NWPCA layout. Other pallets use the full footprint. These checks assess static stacking without simulating transport forces.

Validate also flags a non-stackable item or loaded pallet with a unit resting directly on it.

Inside placed pallets

Validate also checks the items inside each placed pallet in the pallet's own coordinate frame, applying hard rules only and leaving center-of-gravity balance to the container check.

Findings appear as one card per pallet and rule, with an affected-unit count and a button to select that pallet by name. On a severity tie, the card shows the figure furthest past its rule’s limit and names that unit; the selected-pallet panel names it too.

The rules include Pallet bounds, Non-stackable item loaded and Through the rack body; rack-body collision and support checks require usable, compatible voxel data.

Unplaced pallets are not checked.

In the report: The PDF export includes a compliance section with the center-of-gravity lines, the violations and the container specifications, and a securing plan page per container (below).

Securing plan (calculated)

LOP calculates, for each container, whether the cargo stays in place under the accelerations of the CTU Code (chapter 5): by friction, by blocking against the walls and other cargo, and, where a unit is not blocked, which fill or lashing would hold it.

• Transport. By default, sea containers are calculated for road, combined rail and sea area C (unrestricted), and trucks for road (EN 12195-1). A plan can declare another transport in Transport & handling (below). Air ULDs are not calculated: the CTU Code does not cover air transport. Tanks and custom containers are not calculated either.
• Friction. A factor of 0.3 for every pair of surfaces, the CTU Code’s value when the surfaces are not verified (Annex 7, 2.2.2.3), or the lower value the Code’s table gives: a plastic pallet on plywood 0.2. When a plan declares wooden pallets on a clean, dry plywood floor, the factors come from the CTU Code’s table instead (Annex 7, Appendix 2): 0.45 for a wooden pallet on plywood, 0.5 on cardboard.
• Blocking. A unit counts as blocked toward a wall when the voids between it and the wall, through the cargo in between, add up to at most 100 mm. This is LOP’s limit, stricter than the CTU Code’s 150 mm (Annex 7, 2.3.6). A blocking unit must overlap it by at least 50 mm in height and across. A unit counts as blocked only where its contact with the cargo ahead covers its centre of gravity across, or two contacts bracket it: an off-centre contact can let it turn. Contacts under 50 mm are not counted.
• Walls. ISO containers (dry, reefer, ventilated, open top) are rated at 0.6 P on the sides and 0.4 P at the front and door ends (P = payload); EU box and reefer trailers at EN 12642 Code L (front 0.4 P up to 50 kN, rear 0.3 P up to 31 kN, sides 0.3 P), or Code XL when declared (front 0.5 P, rear 0.4 P, sides 0.4 P; CTU Code 6.6.7). Curtainsiders, open-side curtains and North American vans have walls with no rating in this model: they block the cargo, and no load on them is checked; an EU curtainsider declared Code XL is rated as Code XL. Flat racks have end walls rated at 0.4 P (ISO 1496-5, the test load for a solid end wall) and no side walls and no doors. Flatbeds, step decks, lowboys, RGNs and platforms have no side walls and no end walls. Where there is no wall, nothing blocks the cargo: a unit that can move toward an open side is not blocked, however close it stands to the edge.
• Fills. For each block of cargo that is not blocked, and each unit that can move on its own, the first gap on its way to a wall gets a fill: battens across the doorway at the door end, where there is a door (5 × 10 cm, CTU Code Annex 7, Appendix 4), dunnage bags sized to the gap and the force elsewhere, and void filler where the gap is wider than the largest bag. Nothing is filled toward a side or end with no wall, not even a gap between two units: there lashing is the only restraint listed.
• Lashing. The number of top-over lashings (webbing LC 2,000 daN, pre-tension 400 daN) that would hold the same cargo, from the angles of both strap legs: by EN 12195-1 when the transport is road only, else by the CTU Code (Annex 7, 4.2.7: the vertical force of a lashing taken as 1.8 × its pre-tension). Toward a wall it is the alternative to the fill; toward a side or end with no wall it is the only restraint. ISO 1496-1 asks for at least 8 anchor points per side in a 40′ and 5 in a 20′, which usually makes blocking and filling the method in a container. For a flat rack, ISO 1496-5 asks for at least 8 anchor points per side on a 40′ and 5 on a 20′, each rated at least 3,000 kg in any direction, together at least 0.6 P across and, where the end walls are missing or weak, 0.4 P lengthwise (CTU Code informative material 1.6.9; CTU Code 6.2.11). LOP holds this minimum for its flat racks, never the positions or ratings of a unit’s own anchor points.

Transport & handling

Each plan carries one set of settings for what the securing calculation assumes, under Transport & handling in Plan settings. A new plan starts with a copy of the organization's defaults, if an Admin has saved them under Settings → Organization; otherwise it starts with LOP defaults. Choosing another value declares it for this plan.

Copied declarations keep the Admin's name and date and are marked organization default in the plan and on the PDF's securing page. Changing an entry makes it your declaration; unchanged entries keep their source. Later changes to the organization's defaults never change an existing plan. The vehicle rules can be copied; each truck's own vehicle data stay with its plan.

A declaration is yours: the calculation takes it as stated and does not check it. Declare Code XL only for a body certified and marked to EN 12642 XL. LOP records who made each declaration and when; the Validate cards and the PDF page that use a declaration name it and who made it. A change clears the earlier Validate results: run Validate again to see the cards under the new settings. With nothing declared, every container is calculated on the defaults.

Where it shows. Validate lists soft cards, one per container and category: units that can move (toward the front wall, toward the door or sideways), a wall loaded past its rating, a vehicle without rated walls, the lashings needed (naming the form their count used), a lashing that would pull the cargo sideways, or a container that is not assessed. They never fail a plan and never change the solver. The PDF prints a Securing plan (calculated) page per container: the basis, the fills with their positions and forces, the wall loads against their ratings, and the lashings with the form their count used; a flat rack’s page adds ISO 1496-5’s minimum for its anchor points.

Truck axle loads (calculated)

For each truck that holds cargo, LOP calculates the static loads on the tractor’s steering axle and drive axles, on the coupling (fifth wheel) and on the trailer’s axle group, from the vehicle that carries it: the tractor and the semitrailer as one coupled pair, the cargo’s weight and its centre of gravity along the load bed, and the tares. It checks them against the selected rules and the vehicle’s own ratings.

• Vehicle data. Each truck needs its vehicle: the tractor’s empty steering-axle and drive-axle loads, its wheelbase and fifth-wheel position; the semitrailer’s tare and its centre of gravity (or its empty kingpin and axle-group weights from a weigh ticket), the kingpin and axle-group positions, the axle count and spacing; and the plated or technical ratings. A truck without these data is not assessed: a trailer type in the catalogue is a generic example and never gives a legal verdict.
• Status. Data are estimated (the illustrative presets, catalogue values or data not checked against the vehicle) or confirmed (the vehicle’s own data: plates, maker sheet, weigh ticket). With estimated data every finding is a warning; with confirmed data a load past a limit is a hard finding.
• Rules. The rules are chosen, never assumed:
  • EU, international traffic — Directive 96/53/EC Annex I: the axle and axle-group limits by spacing, the tractor’s and the combination’s maximum weights, and the driven axles carrying at least 25 % of the laden combination weight (4.1).
  • Türkiye, domestic traffic — the Highway Traffic Regulation (KTY) Art. 128(1)(d); it sets no driven-axle share.
  • US, Interstate — 23 CFR 658.17: 20,000 lb on a single axle, 34,000 lb on a tandem, 80,000 lb gross and the federal bridge formula over every set of consecutive axles, the span in whole feet as the FHWA table reads it.
  • Without rules, only the vehicle’s own ratings and documented minimums are checked.
  • The steering axle’s 20 % of the tractor’s technically permissible maximum laden mass (Regulation (EU) 2021/535, Annex XIII Part 2, Section D 2.3.4) is a type-approval reference: it shows as a warning and is never a road limit.
• Grouped axles. A group’s load is exact; one axle’s share of it is an estimate (equal sharing assumed) and stays a warning.
• Not modelled yet. Rigid trucks, double-trailer combinations, lowboys, lifted axles and tag or pusher axles (6×2) are not assessed. A spacing the rules publish no figure for is named, never filled in.

Vehicle

The Vehicle section under Plan settings → Transport & handling holds the rules for the plan’s trucks (chosen once for the plan; a truck can name others) and one block per truck: its status, four cited presets (the MAN TGX 4x2 and Volvo FMX13 4x2 tractors, a Schmitz Cargobull curtainsider’s geometry and the Kögel Light Plus capacities), the fields, and Copy to the plan’s other trucks. A preset is a maker’s published example, not your vehicle: data built from presets stay estimated. Tick These are this vehicle’s own data only for data taken from the vehicle itself. LOP records who entered the data and when.

Where it shows. Validate lists the truck’s cards: an axle, the coupling or a weight over its limit, the driven axles or the steering axle under a minimum, an axle or the coupling carrying no load, the bridge formula exceeded, and the state of the data (estimated, missing, not modelled). For a truck assessed from its vehicle data, the older two-support check of the catalogue trailer is not shown, so the cards never contradict each other; a truck without vehicle data keeps that check and gets one card saying its axle loads are not assessed. The cards never change the score or the solver. The PDF prints a Truck axle loads (calculated) page for each truck with vehicle data (PDF Report).

Gross mass (calculated)

For each sea container, LOP adds the masses in the plan the way SOLAS Method 2 sums a packed container (SOLAS VI/2; IMO MSC.1/Circ.1475): every package and cargo item, the pallets, the securing material and the container's tare. It is a worksheet for the shipper's verified gross mass (VGM), not the VGM itself. LOP does not weigh, verify, sign or submit anything.

• The lines. Cargo per product: the units in the container, loose or on a pallet standing in it, times the weight as entered in the plan. Pallets per type: their number times the type's platform weight. Securing material: the mass you enter, or "not entered" (the securing plan gives counts, not masses). Tare: the tare you enter as marked on the box, or the catalogue value, labelled to be replaced. The total is the sum of the lines; a line without a known mass leaves the total not calculated, never zero.
• Against the maximum. The total is shown as a share of the maximum gross mass you enter from the container's CSC Safety Approval Plate, or of the catalogue figure (payload plus tare, not a CSC rating).
• Complete or incomplete. The worksheet says which of the four inputs are missing. Complete means every input is entered; it never means verified.
• Which containers. Library sea containers, flat racks and open tops included. Tank containers, trucks, air ULDs and custom containers have no worksheet.

Gross mass

The Gross mass section under Plan settings shows the calculation for every sea container, with or without entries, and takes four inputs per container: the container number (LOP checks its ISO 6346 check digit), the tare marked on the box, the maximum gross mass from the CSC plate and the securing material in kg. LOP records who entered them and when. It does not ask for a booking, the shipper, a signatory or an authorisation number: those belong to the declaration, which is the shipper's.

Where it shows. For a container with entries, Validate reports a hard gross_over_max finding when the calculated gross mass exceeds the maximum gross mass: a container may not be packed beyond the mass on its CSC plate (SOLAS VI/5). A container without entries gets no such finding; the payload check already covers the catalogue figure. The finding never changes the score or how the solver packs. The PDF and Excel exports list it with the other Layout findings (calculated) (PDF Report).

Carton compression (calculated)

For a corrugated carton (a regular slotted carton, FEFCO 0201) whose Packaging section holds its strength data, LOP calculates how much load the carton should resist under the plan's transit conditions and compares it with the load the carton carries in the layout. It is a screening calculation that tells you which cartons to check with their supplier, not a compression test.

• Box compression (BCT). The measured value you enter (ASTM D642, ISO 12048 and the like), or, from board data, McKee's short formula: 5.87 × ECT × √(board thickness × box perimeter), the perimeter being 2 × (length + width) of the carton's outside dimensions (McKee, Gander and Wachuta, 1963). A carton whose strength data is the supplier's working limit, or is not known, gets no estimate: Max Weight on Top and Crush Strength already apply to it.
• Retained strength. The BCT is multiplied by one retained fraction per condition (a 40 % loss keeps 0.60):

The estimated capacity is BCT ÷ 9.80665 × the factors, in kg. A carton is in an aligned column when every unit resting on it, and every unit it rests on, has its footprint, each edge within 1 mm (LOP's contact tolerance), or when it stands on the floor or a pallet deck. The factor values are LOP's screening choices from these published sources (policy lop.carton-screen/1); their product is not a failure probability.

• The load. The load Validate already checks against Max Weight on Top: the full mass of every unit above whose footprint overlaps the carton's; inside a pallet, the pallet's own column load, plus the share the carton carries of every pallet or loose unit standing on the pallet (see Stacked pallet stability). Where that load is not computed, the carton is not assessed: a pallet above that does not rest stably, a loose unit standing on the pallet that does not rest stably on it, a carton in a rack.
• What is not assessed. The estimate applies only to a box item placed with its flutes vertical whose contents do not support the load; the formula also needs the item's dimensions to be the carton's outside dimensions, a box without hand holes or vents, and a depth of at least a seventh of its perimeter (the formula's range). A measured BCT is that box's own test, so its depth never makes it not assessed. Anything outside that, and any missing input, is named as not assessed, never passed. A double or triple wall is calculated with a note: the formula's published error and the stacking factors are single-wall figures. A test atmosphere stated outside 23 °C / 50 % RH also adds a note, because the humidity factor is relative to 50 %.

Carton transit

The Carton transit section under Plan settings takes the two conditions: the expected relative humidity (0–100 %) and the days under load (more than 0, up to 3,650). LOP records who entered them and when. Without both, Validate names the cartons as not assessed. They belong to the plan: company defaults do not carry them, so every new plan starts without them.

Where it shows. Validate lists soft cards under Stacking and load: Carton compression estimate exceeded (the load is over the estimate), Carton estimate: data missing (strength data or the transit conditions are missing) and Carton estimate: model limit (outside the estimate, or an estimate whose factors carry a note). A carton that carries nothing raises no card. The cards never fail a plan, never change the score and never change how the solver packs. The PDF and Excel exports list them with the other Layout findings (calculated), and the PDF prints the Carton compression estimate (calculated) table (PDF Report).

Loading steps (calculated)

When you click Validate, LOP also goes through the plan the way it will be loaded: step by step, in the printed loading order for Door Loading (back to front; the exports' default loading direction). At each step it checks the cargo already in place, not only the finished load. A plan with loading groups is then unloaded stop by stop, in unload order.

• Support at each step. A unit that is not properly supported when it is loaded, but is supported by a later step (under 70 % supported from below, its centre of gravity too close to the edge of what it rests on, or more weight on the cargo below it than that cargo is rated for), is flagged with both steps. The printed order already lists every unit after the units it rests on, so a finding remains only where a loading group's order loads a unit before what it rests on, or where a pallet stands steady only once the pallet above it is in place.
• Forklift reach. Each pallet is driven straight in through the door, carried 50 mm above where it is set down. LOP checks that no cargo already loaded is in the way, that at least two thirds of the pallet's length rests on the forks (counted from the front of any lower cargo standing nearer the door), and, where its load centre is within the rating, the pallet's weight against the forklift's rated capacity.
• Lifting clearance. Each pallet must be set down either by driving in with the load low and lifting it inside, with the mast and the load backrest staying under the roof, or with the mast outside the door, where the forks reach far enough and the raised pallet passes the door opening. A pallet for which neither works is flagged.
• Unloading stops. At each stop, a unit that can come out only after cargo for a later stop is moved is flagged, and so is a unit left without support once a stop has been unloaded.
• The door end. A unit in the last row by the door that does not have enough support of its own is flagged: it must not lean on the doors when they are opened. Its support finding is listed in Validate as well.

The standard forklift

Reach and lifting clearance are checked for one standard forklift, the same for every plan: a 2-tonne counterbalance forklift (Toyota 8FBMKT20, 4,700 mm mast) with 1,000 mm forks, rated for 2,000 kg at a 500 mm load centre, with a 2,235 mm lowered mast, 1,075 mm of free lift and a 1,200 mm load backrest. These are the maker's nominal figures. The data sheet gives no rating beyond a 500 mm load centre, so capacity is not checked for a pallet whose load centre lies beyond it, which is most full-size pallets: check those against the forklift's load chart. Where the figures cannot settle lifting (the height at which the forks enter a pallet, or whether your site lets the mast stay outside the door), Validate says which pallets were not checked and why. Not checked never means passed.

What is not checked

• Manual handling. Cartons and other units loaded by hand are checked for support at each step, but not for reach, lifting or effort: those depend on the task as measured (the worker, the platform, the grip and how often).
• Fork pockets and side shift. A pallet's fork-pocket positions and a side shift are not modelled; the forks are taken as centred under the pallet.
• Other approaches. Loading from the top or the sides is not assessed, nor is a container without a rear door. Turning room outside the door, dock and ramp ratings and the forklift's full load chart are not checked.

Where it shows. Validate lists these cards under Loading steps: one card per container and finding, naming the first unit and its step, how many more units share the finding and at which steps, with a button for each unit. The step numbers are those the PDF, CSV and Excel exports print for Door Loading; an export in another loading direction numbers its steps differently. The cards are soft: they never fail a plan, never change the score and never change how the solver packs.

Heavy parts (calculated)

For every placed unit of 1,000 kg or more (one item’s weight, loose or on a pallet), LOP states its mass and where its centre of gravity is, in millimetres from the corner of its box as placed: L from the face toward the front wall, W from the left face, H from the bottom.

• CAD parts. The centre of mass LOP stored when it processed the file, under one uniform density: from the part’s solids (tier 1) or from the closed bodies of its mesh (tier 2), turned into the orientation the part is placed in. Only these two are printed as a centre of gravity.
• Not given. A part whose file holds no closed solid, so that only the centre of its surfaces is known (tier 3); a part processed before LOP stored the solid centre of mass; a part turned at an angle whose turned centre of mass is not stored for the plan’s copy; and a part whose stored point lies outside its box. Each reads CoG not given, with the reason.
• Box items. LOP holds no centre of gravity for a cuboid or a cylinder: it reads the box centre, a geometric centre, not a measured CoG. LOP’s other calculations (the container’s CoG line, the securing plan, the axle loads) assume that point for it.

The CTU Code makes the consignor responsible for notifying the packer of a package’s centre-of-gravity offset (4.2.2). For a part made of different materials, use the maker’s figure.

Where it shows. At the foot of the item list in the editor, under Heavy parts (calculated), once a heavy unit is placed, and on a Heavy parts (calculated) page of the Standard and Detailed PDF, after the securing pages. A plan without a heavy unit shows neither.

Next Steps

• Understanding Scores — how constraint satisfaction translates into quality scores
• Manual Editing — resolving violations by adjusting placements
• Items: Properties Reference — how to configure fragility, orientation, hazmat, and crush limits on individual items