These triangles are Compulsory Reporting Points (CRP) and, as the name implies, have to be reported upon passing. They have to be overflown during the visual arrival, unless otherwise instructed by ATC or requested by the pilot. The respective coordinates are published in the VAD Flip. Just for further information, these CRP are located at or close to prominent landmarks, to facilitate the determination of position.
In real life these information are publicly available. I.e. Nordholz ETMN.
Edit: Just read the post again, the coordinates for the highlighted Initial RWY07 are not listed in the picture.
