What are deviations?
After every flight, Sitemark detects what has been built on your site: piles, foundations, trenches, roads, fences and more. Each detection is matched to the component in your design. When a detection matches, the component is marked as built. When the as-built situation differs from the design by more than the tolerance for that component type, Sitemark flags a deviation.
Deviations let you spot construction errors while they are still cheap to fix, without walking the site with a measuring tape.
Which components are checked?
Deviation detection now covers more than piles. Each component type is compared to its design in the way that fits its shape.
Component | What is compared | Default tolerance |
Piles and poles, foundation beams | The position of each component against its design position | 40 cm |
Foundations | The built footprint against the design footprint | 30 cm |
Trenches | The built trench against the design route, and the trench depth against the required depth | 30 cm sideways, 5 cm in depth |
Roads | The built road surface against the design road, in both directions (too wide and too narrow) | 50 cm |
Fences | The built fence line against the design line | 20 cm |
Tolerances differ per type because some edges are sharper than others: a fence line or a concrete edge is easy to pinpoint, the edge of a gravel road much less so. The tolerance a deviation was checked against is shown on the deviation card.
Need stricter or looser tolerances to match your site standards? Your Customer Success Manager can change them per site.
For how accurate these checks are, and why a tolerance is not the same as measurement accuracy, see What accuracy can you expect from deviation detection?
The four types of deviation
The image below shows the three position-based types on piles.
Misplaced
The component was built, but not where the design says.
Piles, poles and foundation beams: the detected component sits more than 40 cm from its design position.
Foundations, trenches and roads: part of the built area extends beyond the design by more than the tolerance. Only that part is highlighted on the map, so you see exactly where it overruns.
Fences: a stretch of the fence strays sideways from the design line by more than 20 cm.
Unexpected
Something was built that does not match any component in your design, for example a pile with no design pile nearby, or a stretch of fence or road where none was designed.
Missing
Part of the design was not built where it should be.
Piles, poles and foundation beams: a design component has no detection, while its neighbours have been built. A component in an area where construction has not started yet is not flagged.
Foundations: part of the design footprint is not covered by what was built.
Roads: the road was built narrower than designed.
Trenches are not checked for being too narrow. From above, a drone sees the open excavation at the surface, whose width depends on how the soil slopes and where the spoil is heaped, not on the trench width you designed. For trenches, depth is what counts.
Wrong depth
For trenches only. Sitemark measures the depth of the trench floor against the ground beside it and compares it to the required depth in your design. A stretch that is more than 5 cm shallower than required is flagged. Each trench is judged on its shallowest stretch, so a deep section cannot hide a shallow one.
Open a flagged stretch to see the required and measured depth, and a cross-section of the trench at its shallowest point. A colour overlay on the map shows the depth along the trench, from green (close to the required depth) to red.
Trench depth checks are in beta. Ask your Customer Success Manager to enable them for your project.
What you need
Your design in Sitemark. Deviations are only calculated against components that are in your design. See How to make your dxf file Sitemark compatible.
The right shape per component. Piles, poles and foundation beams can be points. Foundations, roads and trenches need to be drawn as areas (or centrelines for trenches), and fences as lines.
A required depth on trenches, if you want the Wrong depth check.
A flight with an elevation model, for trench depth.
Working with deviations
The example below shows foundation deviations on the map, with the Deviations group open in the layer panel. The flagged strips are where the built foundation and its design footprint differ.
On the operation map, open the Deviations group in the layer panel. Each component type has its own layer, so you can switch on only what you are working on.
Open a deviation on the map to see its type, the component it belongs to and the tolerance it was checked against.
In the operation table, group by component to see the deviations per component type.
Create a ticket at the deviation to assign the fix to someone on site. See Managing Problems on the Construction Site with Sitemark's Ticketing System.
Good to know
Deviations and progress. A component that is a little off-design still counts as built and is flagged as a deviation. A component built too far from its design to be matched to it (more than 1 m for piles, 30 cm for fences, or less than half of a road or trench segment covered) is not counted as built and shows as Unexpected instead.
Only what is built is checked. Design that has not been built yet counts as remaining work, not as a deviation.
Deviations are recalculated after every flight, so they always reflect the latest state of the site.
Deviation checks run on both solar and wind construction sites.
To see deviations in action, watch our demonstration video.