ground truth1
/ˈɡraʊnd ˌtruːθ/noun
1A fundamental truth. Also: the real or underlying facts; information that has been checked or facts that have been collected at source.
2In remote sensing: information obtained by direct measurement at ground level, rather than by interpretation of remotely obtained data (as aerial or satellite images, etc.), especially as used to verify or calibrate remotely obtained data.
3Information obtained by direct observation of a real system, as opposed to a model or simulation; a set of data that is considered to be accurate and reliable, and is used to calibrate a model, algorithm, procedure, etc. Also: (specifically in image recognition technologies) information obtained by direct visual examination, especially as used to check or calibrate an automated recognition system.
Origin
Mid 19th century; earliest use found in Henry Ellison (1811–1890). From ground + truth adverb, in sense 1 probably after German Grundwahrheit.
ground-truth2
/ˈɡraʊn(d)truːθ/verb
[with object] To confirm or validate directly (information or data derived indirectly), especially (in remote sensing) by direct observation on the ground, rather than by interpretation of remotely obtained data; to make observations of (land, an area, etc.) directly on the ground, especially in order to confirm or validate data obtained indirectly.
Origin
1980s; earliest use found in American Antiquities. From ground truth.