Create Stellarium landscapes from

panoramas

ATTENTION: The publication of a Stellarium landscape created from a 360cities panorama or the implementation of a public demonstration using the same requires the ownership of the rights or the purchase of a license for the used 360cities panorama!

Selection of a

panorama

Stellarium landscapes can only be created from fully spherical 360°x180° panoramas and not from cylindrical panoramas, unless the natural floor area is dispensed with and the area that does not exist in the cylindrical panorama is filled with an artificial image.

The creation of a Stellarium landscape from a 360cities panorama only makes sense if the exact geographic coordinates of the panorama site are known and the panorama has been correctly oriented to the cardinal points or when this can be easily done by yourself based on recognizable landmarks with the aid of www.geoplaner.de and a tool for calculating great-circle distances, e.g. cactus2000.de or movable-type.co.uk. Many 360cities panoramas are neither aligned nor do they offer any clue for an alignment that you can carry out yourself and are therefore ruled out from the outset.

Set the target resolution of the Stellarium landscape

In order to maintain the sharpness of the original image, the target resolution of the Stellarium landscape must not be higher than the resolution of the source panorama from 360cities. If the original panorama has a resolution of 10000x5000 pixels, a spherical stellarium landscape derived from it has a maximum possible resolution of 8192x4096 pixels (next smaller integer powers of 2!).

Producing the input image material for Hugin

The image material required for the production of the Stellarium landscape with Hugin is obtained by means of screenshots from viewing the 360cities panorama in full screen mode.

360cities uses krpano as a viewer to display the panoramas. The display mode "Normal View", which corresponds to the gnomonic (rectilinear) projection, must be set for the screenshots. The field of view angle (HFOV) can only be set approximately and should be between 60° and 70°, but in no case more than 100°. However, if the target resolution is very high, the HFOV angle must be smaller; the formula

HFOV = 270° * Horizontal resolution of the screenshots / target resolution of the Stellarium landscape

may serve as a good guess.

Once the set field of view angle has been used for a screenshot, it must not be changed for the entire project! All screenshots of the project must therefore be taken in one go. The procedure corresponds to the recording process for real-image landscapes, only that the "recordings" are now made virtually using screenshots, which are rectilinear with the selected krpano setting, just like 35mm camera recordings. A screenshot is sufficient for the nadir area if the nadir has been moved to the center of the image beforehand; To be on the safe side, you can take another nadir screenshot crossed by 90°. Screen shots of areas that only show the sky are not required.

During the screenshots, as soon as the HFOV is set, “Hide / Show Controls” should be switched to “Hide”, in particular to switch off the reference arrows to neighboring panoramas. In full screen mode, only the exit button is left as a disruptive element, which can finally be masked out in Hugin.

Loading the screenshots into Hugin, initial fitting and further optimization

All screenshots are now loaded into a new Hugin project like individual photos. Since there can be no parallax or head tilt errors with the screenshot technique, all recordings must be assigned to the same lens (Lens 0), which is to be set to the "rectilinear" type (if you do not change the angle of view in 360cities in the middle of the screenshot Series, you have to load the corresponding screenshots into a new lens or start over). After masking the exit button from each screenshot, the fitting process can be started, in the course of which the correct HFOV is also determined.

The spatial optimization should not cause any problems, since the individual screenshots are excerpts from one and the same completed panorama. A photometric optimization is not necessary, rather set EV = 0, Er = 1 and Eb = 1 for all screenshots. Only the average (mean) EV value in the Fast Panorama Preview has to be increased if the Hugin panorama threatens to become too bright for a Stellarium landscape.

Further processing of the panorama

The further procedure corresponds to the procedure for creating a landscape from your own photos, in particular with regard to removing the sky and the correct alignment of the panorama as well as its integration in Stellarium. Corrective vertical scaling should not be necessary, however.