Monday, May 28, 2007

Virtual tour - Kasperk Castle

Kasperk Castle (Kašperský hrad), situated 3 km north of Kasperské Hory in Czech Republic is a ruin of a gothic castle build in 14th century for defense and observation purposes. The exhibition inside reveals the history of the castle as well as of the gold mining in the area.

Wednesday, May 23, 2007

Nodal Point confusion made clear

One of the important issues in panoramic photography is the proper setting of the vertical rotaton axis of the camera to what people often call the nodal point. Although "What is the nodal point?" is one of the most frequent questions when it comes to panorama creation the term of "nodal point" is being misinterpreted in this context in vaste majority of cases. As I will show you in this article the "real" nodal point is not what one should be concerned about when adjusting his photo equipment.

When turning a camera around or changing the point of view position you generally experience an apparent shifting of foreground objects relative to background objects which is called parallax. When taking the pictures for a virtual tour scene you want to rotate the camera around a line that runs through (or as close as possible to) a certain point such that the parallax error is completely eliminated. Failing to do so may result in problems with the stitching process and will require a lot more work with the possibe need for image retouching.

So first of all, in order to set the terminology to rights I will provide you with the proper definition of the nodal point. In fact, it consists of two points - the front and rear nodal point. In order to understand this issue let us first define:

  • The principal planes (front and rear) which have the property that a ray emerging from the lens appears to have crossed the rear principal plane at the same distance from the axis that that ray appeared to cross the front principal plane, as viewed from the front of the lens.
  • The principal points which are the points where the principal planes cross the optical axis.

If the medium on both sides of the optical system is the same (e.g. air), which is indeed our case, then the front and rear nodal points coincide with the front and rear principal planes, respectively (see the diagram). So there is nothing like a single nodal point to which so many pano tutorials are wrongly referring.

On the other hand, the most common explanation of nodal (or principal) point as being usually heard from pano photography folks says that it is the point inside a lens where light rays converge and flip over before being focused onto a film plane or a digital sensor. It should also be the place where the entrance pupil of the camera is situated. So far so good, this explains where the point to which one should set the center of rotation for shooting panorama is situated. However, using the term "nodal point" is absolutely improper here and one shoud rather think of a different term to avoid confusion. I personaly prefer naming it "pivot point". By the way, it is also worth noting that the nodal point is not the same as the film/sensor plane (sometimes marked at the bottom of cameras) as some photographers think.

In practice determining the pivot point of a lens is quite easy to do visually. The only thing you need is two vertical features that you can use as reference lines, for instance a flag or light pole, corner of a wall etc. Set one of them very close to the camera (1 meter or so) while the other one stays far away. Take two shots at different angles so that the vertical features you chose are close to the right or left edge of the frame, respectively. Most likely you will see the parallax shift of the objects. Adjust the corresponding rail on your panoramic head (the one that changes the vertical axis of camera rotation) so that you reduce the parallax. Eventually you should be able to eliminate it entirely which usually requires few iterations depending on how accurate your judgement was in each step. By checking the test images down to a pixel resolution a sub-milimeter accuracy in the setting of pivot point can be achieved.

Monday, May 21, 2007

Virtual tour - Silesian-Ostrava Castle

The Silesian-Ostrava Castle (original czech name "Slezskoostravský hrad") is one of the most historical and cultural monuments of the city of Ostrava. This originally gothic castle was built at the end of the 13th century. In mid-16th century it was rebuilt into a renaissance chateau. It was restored recently after many years of dilapidation, caused by coal mining under the castle. It is definitely one of the most important tourist attraction of the city that worth seeing. Our virtual tour brings you to this remarkable place.

Saturday, May 19, 2007

High Definition Viewer from Microsoft

Just a few days ago Microsoft released a Beta test version of their new utility called HD View. This viewer was developed by Microsoft Research's Interactive Visual Media group to aid in the display and interaction with very large images. Thus, it's not just a panoramic photography viewer but it is generally following the demand to visualise high resolution visuals over the web as well as the increasing resolutions of modern digital cameras. With this tool, displaying images of gigapixel resolution shouldn't be a big deal even in web-based applications.

Apart from the "on-the-fly" image loading capability (so that just the current view is loaded with the necessary level o details) for the panoramic photography branch the most unique and powerful feature of HD View is the zoom-dependent perspective transformation which is greatly reducing image distortions present with other current viewers.

As Microsoft research lab staff claims, it should:

  • allow smooth panning and zooming on large images,

  • only download enough data to create the current view (and possibly look ahead to the next), and

  • always display the current field of view with an appropriate projection. This means that when zoomed way in you should be presented with a standard perspective projection providing a sense of immersion, and when zoomed out you experience a curved projection so that get a full overview of the scene. In between the projection should smoothly transition.

  • Finally, it should be easy to create your own HD View content and present it to the world via the web.

The following video shows all the main features of this new viewer:

At the moment HD View is an ActiveX browser component, thus the first time you use it you will be asked to install it. It also only runs in Internet Explorer under the MS Windows. Hopefully there will be more support for other browsers and operating systems added in the future versions of HD View. Microsoft also announced that the tone adjustment functionality (very usefull for huge images that typically has very deep dynamic range) will be released in a new version soon.

Friday, May 18, 2007

Virtual tour - The Huntington Library, Art Collections, and Botanical Gardens

The Huntington Library, Art Collections, and Botanical Gardens is one of the most spectacular places you can visit in the U.S. It was founded in 1919 by Henry Edwards Huntington, the famous railroad and real estate developer, at the place that later became the city of San Marino. On its 120 acres of gardens you can find one of the world's largest botanical collections of over 14,000 different species of plants, three art galleries and a library with magnificent collections of paintings, sculptures, rare books, manuscripts, and decorative arts.

Now you can explore The Huntington virtually. Yesterday, we posted 27 interactive panoramas taken throughout the whole garden - they are all available on The scene below is a 360° view on the small part of Desert Garden which is one of the largest and oldest assemblages of cacti and other succulents in the world:

Thursday, May 17, 2007 featured on ProgrammableWeb

Last month, as the project is partially based on Google Maps API it was submitted to ProgrammableWeb, a website dedicated to all kinds of mash-ups and APIs. was awarded a "Mashup of the Day" and soon gained high user ranking and popularity, both being in top 10% of all the sites listed. This is exactly the type of feedback that stimulates our enthusiasm for keeping the project up and running and bringing new features to our users.

Neverheless, nothing is perfect so we are open to any critisizm as well. Is there anything on you would wish to be changed or designed in a different way? Is there any functionality glitch? Are you satisfied with the quality of the virtual tours themselves? Any comments and suggestions are welcome.

Wednesday, May 16, 2007

Virtual tour - Loreta Square in Prague

Just to give you an example of how the virtual tour looks like you can enjoy a virtual visit to one of the most beautiful european cities and increasingly popular destination - Prague, capital of the Czech Republic. The view below was shot at Loreta Square in the historical district of Prague.

How to use our virtual tours:
Looking around the interactive panorama is very easy and intuitive: for panning and tilting click the left mouse button and drag the mouse to any desired direction. While panning/tilting, you can also use the "control" and "shift" keys to zoom in and out. Alternatively, the same functionality is provided by the controls on the bottom bar of the virtual scene.

3Dtour Blog launched

It has been about three months now since the new Virtual Tour project at was launched. At this moment you can find there nearly 100 interactive panoramas from different locations mainly from Czech Republic, but there are also some from Slovakia and California. Indeed, there's much more to come soon as new virtual panoramic scenes will be added more-less regularly.

This blog will be dealing with a variety of virtual tour topics as well as featuring some live examples of high resolution spherical panoramas. Panoramic photography itself is almost as old as the subject of photography. However, to make a panorama interactive one needs to have a computer and appropriate software capable of displaying such an image in the real time, which is nowadays almost any computer but it wasn't like this some 5-10 years ago. Thus, the "art" of virtual tours is relatively new subject which gained significant popularity in just about last two years or so.

If you find this topic the same hot, stay tuned!