Why are my area measurements negative?

[[Da...]]

I am using GOM inspect (free version) to measure the area of a cross section. 

my steps to get to where I am are:

- Import part
- import mesh
- define plane
- create cross section using plane
- fill gaps in cross section using section tools and remove random parts i am not interested in
- using interactive tool to add area measurement (setting nominal area manually to 435mm^2 which is the nominal value for the area i expect)

 

output

Edited March 28, 2023

[[Da...]]

I should add the expected output would be

Nominal +435
Actual 427
Dev -8

[[Na...]]

Hello David,

please check the normal direction of the mesh. If the surface is "inside out", you will get a negative value. You can invert the surface via Operations -> invert selected normals.

Regards,
Nanno

[[Je...]]

Hey David,

 

an additional comment to the inspection you have performed.

I read 'Throat Area' as name for the inspection and you explained that a section is used (so purely 2D). With the background of my daily work I know Throat Area as the contraction of a flowed through passage, namely the smallest possible area with perpendicular orientation to the flow direction that can be placed inside the passage. The end result is a true 3D surface with distortions/twist/bending.

For the aerodynamic problem to determine the 3D Throat Area the software offers in the 2022 version a geometric alternative which shows a very high / strong correlation to the aerodynamic result (eg delivered by a CFD-simulation). 

Here a screenshot of the geometric 3D Throat Area in Blade Inspect Pro 2022.
Beside the size of the nominal and actual surface you also have the position of the 3D Throat Area analysed. Take the upper right portion, which is out of tolerance as indicated by the red coloring.

Maybe this is some additional help for your inspection.

Regards, Jens

[[Ji...]]

I also experienced a negative value when calculating areas.  It turns out that if the software is measuring the area of "space", or holes, it is a negative value.  If you are measuring the area of an actual surface, the area is positive.  So, it comes down to the vectors of the surface.