display of 2d directed viewing cone

Exif Metadata may not only declare the viewing direction but also/additional focal length, which could be used to calculate and display a directed 2d cone. Of cource the angle differs with the lens/sensor used. As Nikon seem to declar the focal lengh in relation to the sensor size( e.g. 35mm) the solution could be to use 35mm as reference.
Examle snippet of EXIF Metadata:
GPS Bild Richtung |157,20
Brennweite in 35mm F|31
Brennweite |31,0 mm

I think it is useful to have it in a seperate layer and not directly within the thumbnail layer. So why not having a differentiation of types of PhotoLayers.

So the following config will result in a layer with directed viewing cones only.

<PhotoLayer type="viewingcone">
    <l:Name>hankos_vacation</l:Name>
    <d:Title>Where the hell was Hanko</d:Title>
    <s:CRS>EPSG:4326 EPSG:31466</s:CRS>
    <Directory recursive="true">/home/rubach/privee/200910_australia/</Directory>
    <ImageSize>100</ImageSize>
  </PhotoLayer>