How to build Stellarium landscapes from photographs of your own (1/4)
What you need in order to start work
Ordinary digital camera or smartphone
The resolution of the camera determines the achievable resolution of the landscape to be created:
- 1 MP (MegaPixel) is sufficient for 2048x1024 landscapes (angular resolution approx. 0.18° = 10.8') in good quality
and for 4096x2048 landscapes (angular resolution approx. 0.09° = 5.4') in limited quality
- 4 MP is sufficient for 4096x2048 landscapes (angular resolution approx. 0.09° = 5.4') in good quality
and for 8192x4096 landscapes (angular resolution approx. 0.044° = 2.6') in limited quality
- 16 MP is sufficient for 8192x4096 landscapes (angular resolution approx. 0.044° = 2.6') in good quality
and for 16384x8192 landscapes (angular resolution approx. 0.022° = 1.3') in limited quality
The horizontal and vertical number of pixels in Stellarium landscapes must be a natural power of 2.
When deciding on a specific resolution, also take into account the storage space requirements to be expected for a Stellarium landscape (PNG format, maximum compression):
- approx. 2.5 MB for 2048x1024 landscapes,
- approx. 10 MB for 4096x2048 landscapes,
- approx. 40 MB for 8192x4096 landscapes,
- approx. 160 MB for 16384x8192 landscapes.
You should also consider the ability of conventional graphics cards to handle such texture file sizes at all (alternative for high resolutions: the multi-image format).
Important: The use of a tripod is not required at any point in this manual ; the entire manual is based on working without a tripod . If you want to use a tripod, please consider:
- The elevation of the lens with a tripod should be set similar to the height of the naked human eye so that the perspective on which the landscape is based corresponds to the human perspective
- You still have to photograph the nadir area without a tripod because it is in the way
- The mere use of a tripod alone does not prevent parallax errors. For this you also need a special rotating head, which ensures that the objective lens of your camera remains in the same place at every angle of rotation and inclination. Such accessories are available from Nodal Ninja, for example - and come at a price.
- The use of a tripod is only worthwhile with cameras that are too heavy and too high-resolution to be able to take shake-free recordings with them.
Memory card(s) with sufficient storage space and a powerbank or spare batteries / rechargeable batteries
Equip your camera with a memory card with sufficient free storage capacity and take additional memory cards with you if necessary. With a smartphone, use e.g. cloud memory when local memory is running out. A JPG-compressed photo occupies up to about 0.5 byte / pixel. For a camera with a horizontal field of view (HFOV) of 54° (with 1:1 zoom) you need to create a stellarium landscape
- with 1:1 zoom about 100 to 150 shots
- with 2:1 zoom about 400 to 600 pictures
- with 3:1 zoom about 900 to 1300 pictures
Also remember to take spare batteries / rechargeable batteries or a fully charged power bank with you so that you do not have to stop the recording series prematurely.
Computer with sufficient CPU and graphics performance
A modern system with 3 GHz dual core CPU, 4 GB RAM and OpenGL-capable graphics is sufficient. Note that Stellarium requires the OpenGL standard. If there is no hardware OpenGL capability, an OpenGL software emulation such as Mesa must be used. The fitting and the creation of the panorama are CPU-intensive processes for which sufficient computing power and RAM must be available. A system with the above equipment needs about 1 hour for the initial fitting. On less powerful systems, the initial fitting can quickly take half a day to a full day.
A requirement for applications such as GoogleMaps, www.geoplaner.de, distance calculation script, etc.
Panorama software Hugin
Combines a series of photos into a panorama. Hugin is open source software and available for all major computer platforms.
Transparency- and multilayer-capable image processing software
To edit the panorama, especially to remove the sky, you need transparency and multilayer-capable image editing software such as The GIMP or Adobe Photoshop.
Scientific calculator and knowledge of trigonometry
In order to be able to control, for example, the elevation or depth angle of certain landmarks or soil features in the finished landscape, you should be familiar with "arctangent" and the like.
Preliminary considerations and precautions for the photo session
Lighting and weather conditions for photo shooting
Choose a day with a good, clear sight of the horizon. The meteorological visibility should be at least 20 km, preferably 25 km and more (especially when taking pictures from high mountain peaks or when sea areas form part of the horizon). Haze, dust, fog, air filled with precipitation or rain shafts in nearby showers, which obstruct the clear sight of the horizon, are not suitable conditions for taking a panorama. Likewise, you should refrain from taking panorama shots in high winds or gales, as wind-triggered movements of trees and branches will prevent the snapshots from being properly fitted later.
During the shooting session - for which you have to plan at least 20 minutes for 100 snapshots! - there must be consistently good lighting conditions, either with an evenly overcast sky (especially if you don't want the casting of shadows) or, if you want to achieve vivid colors, in uniformly sunny conditions without cloud penetration in front of the sun, whereby you then have to accept the casting of shadows and also the risk that the sun may outglare the horizon section below it (especially important for panoramas taken at the seaside). To avoid this and to prevent the shadows from getting too long, photos should only be taken when the sun's altitude is at least 20° (better 30° and more). It is also to be considered that in the case of sunshine the reflection characteristics of the ground, depending on the azimuth, are more uniform the higher the altitude of the sun. Basically - whether sunny or overcast - you should no longer take pictures when the sun's altitude has dropped below 10°, as it is then no longer bright enough for good daylight panorama pictures.
Important: Do not mix snapshots that were made in very different lighting conditions. The result is practically always disappointing.
Site selection and verification
For the panorama picture, select a site with a clear sight of the horizon in as many directions as possible and with recognizable and reliably identifiable landmarks - the latter is important in order to be able to determine the cardinal directions later on in the finished panorama (the direction of paths and streets shown on maps can serve as a substitute). Identify your location with the help of a GPS logger or a combination of maps and satellite images (e.g. www.geoplaner.de or Google Maps) so that you can determine the latitude and longitude of your location with an accuracy of 5 degrees (corresponds to 0.036" or an accuracy 1.11 m) as well as the altitude above sea level in meters.
Choose a stable and non-slip position above a clearly identifiable ground feature (stone, tuft of grass, etc.), with regard to which you can continuously check and correct your position, as you have to turn around your own axis several times for the series of snapshots.
During the series of snapshots, your own position must be maintained as precisely as possible and you must continuously check whether you are still standing in the same place. A displacement of just 50 cm results in clear parallax effects with close objects, disturbing or even preventing the subsequent successful assembly of the panorama (parallax = optical shift of close objects in front of a distant background by changing the position of the observer)
Highly frequented locations (e.g. tourist hot-spots) are only suitable for taking pictures in times of low frequency, as people passing close significantly disturb the concentration required for taking pictures of this type and, for legal reasons (right to one's own picture), no close-ups of people should appear on the final panorama. If close-ups of people are unavoidable, the corresponding solid angle section must be photographed several times in order to be able to remove the people from the overall panorama later by masking them out.
Important: Measure your eye height / lens height, preferably at home (with shoes) on level ground, because this value must be taken into account in calculations. If you work with a tripod, this value must be measured on site after the tripod and camera have been set up. Always perform measurements with the camera oriented horizontally.
Performing the panorama shooting session
Find a direction easy to recognize and memorize as a starting direction for the panorama picture.
Beginning with the horizon, the snapshots are to be taken strictly "line by line" in a clockwise direction, whereby the angle of inclination of the camera must remain approximately the same in one "line". Adjacent photos of a "line" must overlap sufficiently so that the center of the previous image can still be seen clearly in the left edge area of the current photo to be shot. In the case of a camera with a horizontal field of view of 54°, for example, this leads to increments of 20° to 25°, so that about 15 to 20 photos are to be expected for the 360° round.
When you have reached the starting direction again, you begin with the next shooting "line". To do this, the angle of inclination of the camera is increased so that the image areas around the central line of the previous shooting "line" can still be seen well at the upper edge of the photos to be made now (overlap!). In the case of a camera with a vertical field of view of 40°, this means an increase in the angle of inclination by around 12° to 15°. Again, while maintaining the angle of inclination, a complete 360° round of photo shootings has to be finished and, when arriving at the starting direction again, the camera has to be tilted to the next shooting "line".
This principle is to be continued until arriving at the nadir. On the penultimate round of shots, which should include 8 shots with a 54° camera, you should already be able to see your own toes. Otherwise, as little as possible of your own clothing or equipment should get onto the images (these areas are masked out later when the panorama is created and, thanks to the sufficient overlap with other images, do not get into the final panorama).
The final round of shots is dedicated to the nadir itself, i.e. the area where your own feet were previously. For the nadir shootings, stand with your legs apart over the nadir and photograph the nadir area vertically from above (it doesn't matter that feet and legs can be seen at the edge of the picture). Three such recordings with clearly distinct azimuth angles should be made (e.g. one recording perpendicular or at a 60° angle to the other).