The Astrolabium Planum was printed at Augsburg in 1488 under the name of Johannes Angelus, the German astronomer and physician Johann Engel. Most of the volume is working astrological apparatus, tables for dividing the houses and instructions for their use. What has kept it in circulation is a different section: a series of images, one for each of the three hundred and sixty degrees of the zodiac, each with a short accompanying text describing a figure or a scene.
The images are not his invention. Degree by degree image material was already circulating in manuscript and is generally traced back to earlier compilations associated with the name of Pietro d'Abano, itself standing on older astrological sources, and the printed book gathers and fixes what had been variable. That distinction matters for how the atlas cites it. The Astrolabium Planum is the earliest widely available witness to this body of imagery rather than its origin, and a claim that a particular degree image begins here needs checking against the manuscript tradition rather than assuming the printed edition is the source.
A degree image system does a particular job in practice. Ordinary astrological reading works with sign, house and aspect, which are relatively coarse divisions, whereas an image attached to a single degree gives the interpreter something concrete to say about an exact position, and that exactness is the appeal. It is also the weakness. A birth time uncertain by four minutes moves a chart by roughly a degree, so the apparatus depends on a precision the underlying data usually does not support.