Big Ben's Panorama Tutorials

Technical Background

• Projection Formats
• Understanding Coordinates

Projection Formats

PTStitcher will output a wide variety of projection formats, however PTViewer generally uses only two; equirectangular and rectilinear.

One of the most common faults/queries relates to cylindrical panoramas.  Cylindrical panoramas need to be converted to equirectangular to be displayed properly.

Understanding Coordinates

PTViewer uses two types of coordinates, absolute and relative. 

Absolute coordinates are measured in pixels and measured from the top, right corner of the image.

Relative coordinates are measured in percentages from the top right corner of the complete 360x180° image. Confusion can arise with partial panoramas, where the edge of the image is not defined by 0/100%. PTViewer currently does not correctly display the relative coordinates for partial panoramas. You can calculate relative coordinates from absolute coordinates by calculating the distance of the coordinates from the centre of the image, converting them to percentages and adding this to 50% (the centre of an image is X50,Y50)

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x,y - absolute coordinates
X,Y - relative coordinates
w - width of the image (pixels)
h - height of the image (pixels)
pfov - horizontal FOV of the image

X = 50 + (x - w/2) * (pfov/3.6w)

Y = 50 + (y - h/2) * (pfov/3.6w)

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Why use relative coordinates?

Relative coordinates are useful if you need to develop a tour at different resolutions for different uses (e.g. low resolution for web plus high resolution for CD). Altering the size of the panorama images will then have no effect on the positioning of the coordinates.  You can simply swap the panorama images of different sizes and everything should still work.