Specter provides various geometric measurements such as areas and volumes. These can either be calculated automatically or transferred from the IFC model.
In this article, we will show you:
how these values are calculated
what you should pay attention to
and why the same “area” is not always to be understood in the same way.
. Overview: Dimensions in specter
When uploading an IFC file, specter automatically checks whether it already contains dimensions.
If dimensions are available, specter imports them directly from the file.
If dimensions are missing, Specter calculates four key measurements independently - regardless of the data model or export settings in the CAD program.
These automatically generated dimensions are available for each object and form the basis for numerous functions in the tool.
2. The four automatically calculated dimensions
1. Total area (net):
The total area describes all visible exterior surfaces of an object, including openings (e.g., window reveals). This means that even if an opening such as a window is not explicitly modeled, its area is still included in the calculation.
2. Base area (net):
In Specter, the base area is calculated as a 2D projection of the object onto the XY plane - it therefore corresponds to the top view. This means that you obtain the area of the shape that would be visible if you were looking at the object from above.
Note:
For simple objects (e.g., T-shaped objects), this value is usually accurate.
For more complex shapes, deviations may occur. In this case, the area is calculated as a polygon that encloses the outer contours of the object.
3. Surface area (net)
The surface area is calculated as:
Total area – 2 × base area
It describes the outer surface area of an object, i.e., all side and end surfaces, but without the bottom and top.
Example:
For a cuboid, the surface area corresponds exactly to the sum of the front, back, left, and right side surfaces.
4. Volume (net)
The volume is calculated directly from the geometry of the model.
All recesses and openings (e.g., shafts, windows, or doorways) are taken into account - provided they are present in the model.
Empty spaces that are geometrically included but not visible are also included in the calculation and deducted accordingly.
Example:
A massive cuboid with a modeled cavity in the middle has a smaller volume than the same cuboid without a cavity.
3. Net or gross – which counts?
In specter, all measurements are calculated as net values.
This means:
Openings and recesses (e.g., windows or doorways) are taken into account and fully incorporated into the calculation.
No gross areas or volumes are shown.
If you require gross values (as output by default in some CAD programs), these can be evaluated in specter via Qto imports.
See the article on this topic: https://help.spectercloud.io/en/articles/406803-ifc-properties-when-dimensions-are-not-delivered-in-a-standardized-format
4. Special feature: Base area and lateral surface are idealized
Important to know: The base area calculated in Specter does not always correspond to the actual contact area of an object.
For T-shaped or complex-shaped components, the base area is calculated as the projection of the upper surface onto the XY plane (top view).
This may result in discrepancies between the calculated floor space and the actual space occupied.
This simplification is due to technical reasons and should be taken into account in exact calculations.
Example:
IIn the following sketch, only the area marked in green (top view) is used as
the base area for a T-shaped object - not the area actually occupied (red).
Since the envelope area is calculated from the total area, deviations may occur. This depends on whether and how openings (doors/windows) are present in, for example, a wall.
5. Summary
Four automatically calculated dimensions:
If the IFC does not provide its own dimensions, Specter calculates the values for total area, floor area, envelope area, and volume independently of the IFC export.
Net instead of gross:
All measurements are calculated as net values.
-> Openings and recesses (e.g., windows or doorways) are taken into account and deducted from the result.
Special feature base area & lateral surface:
These dimensions are idealized.
-> For complex shapes (e.g., T-shaped components), simplified projections are used—this may result in deviations from the actual contact area.
No Qto data:
External Qto data from CAD programs is not used for these calculations. Gross values can only be analyzed via Qto imports.