Carpets hang from the parapets - see Davies.

Carpets hang from the first floor window - see Davies. The church was badly damaged in the war.

See Giotto to Durer page 344. The frescoes in Spoleto were Filippo Lippi's last work; he died there in 1469.

This work celebrates the same event as Crivelli's Annunciation. It bears the words Libertas Ecclesiastica above a model of Ascoli Piceno and in front of the arms of the town. The inscription at the bottom makes it clear that this is a civic picture; there are records of its hanging in the chapel of the Town Hall.
Gabriel's words of greeting are inscribed across the painting.

Another very geometric Annunication from a Franciscan church. The vanishing point is sharply offset to the right. There are a number of similarities to the Crivelli. The background behind the Virgin has an interesting design.

Bars in front of the first floor windows in Perugia - see Davies. They might support sunblinds as here.

The device of placing the Angel in the street and the Virgin within her chamber was used by Crivelli in 1482. There are noticeable similarities in the details in both Annunciations, though this work is much smaller.
Detail: The Virgin

Davies notes the influence of Bellini's Annunication in the British Museum sketchbook on Crivelli's composition. See also Giotto to Durer p 143.

The red lines represent a grid that divides the painting vertically in quarters and horizontally in thirds. The grey lines indicate the vanishing point. The figures seem to be enclosed by two similar (in the geometrical sense) triangles.
Useful references to follow this up might be Michael Baxandall pp. 91 - 101 of Painting and Experience in 15th century Italy, where he argues that artists set out to flatter their patron's ability to 'guage' and Hall and Robson's analysis of the perspective of this painting in volume 8.2 of Computers and the History of Art (NAL pressmark PP.108.E).
Please note that the lines were drawn using a drawing program (Paint Shop Pro), not AutoCad, and so are just an indication.

More virtuoso perspective from Crivelli - this time the figures in the distance are not 'enlarged', and the focus is firmly on the Blessed Gabriele's hands right at the front of the picture plane.
A vision of the Virgin and Child appears to the Blessed Gabriele as he prays in a wood near the convent of S. Francesco ad Alto, Ancona. Gabriele Ferretti, a much-venerated superior of this convent, died in 1456. The iconography of the Blessed Gabriele's vision is paralleled with that of Saint Francis when he received the stigmata.