Hi, I cannot answer all of your questions but I hope my description will help you.
Assume you have multiple images (Img1, Img2, Img3, Img4, Img5) covering a 360x180 field-of-view. The images are stitched using hugin and projected onto a full spherical surface. The assumption can be extended to images with limited field-of-view and different projection surfaces. Hugin does the stitching with optimization (or bundle adjustment) of orientation (yaw-y, pitch-p, roll-r) and lens correction parameters by using control points and line points. *Control points*: The control points are matching points in the overlap region across multiple images (Read more about matching control points here [1]). Let's assume Img1, Img2 and Img4 have an overlapping area with one matching point (x_Img1, y_Img1) <-> (x_Img2, y_Img2) <-> (x_Img4, y_Img4). The SIFT or similar features match corresponding points in other images, irrespective of the orientation, size etc [1]. So it does not matter if your photos are landscape or portrait or of different size. Assume that other images (Img3,Img5) have matching control points as well but for simplicity, I am not adding more points here. *Line points*: Assume that Img4 has two line points (one horizontal line H1(x1_Img4,y1_Img4 <-> x1_Img4,y2_Img4) and one vertical line V1(x3_Img4,y3_Img4 <-> x4_Img4,y3_Img4)). Hugin extracts all edged lines per image and checks for the angles, arcs etc to find line points which are exactly horizontal or vertical. I don't have a link to documentation. You can check it in the code to get more details. *Orientation*: Assume that the orientations (y,p,r) for images are Img1<->(y1,p1,r1), Img2<->(y2,p2,r2), Img3<->(y3,p3,r3), Img4<->(y4,p4,r4), Img5<->(y5,p5,r5) *Lens Correction*: Lens correction can have multiple parameters but for the sake of simplicity, assume that there is no lens correction. *Optimization*: The optimization in hugin starts with 0 initial orientation (y1,p1,r1,y2,p2,r2,y3,p3,r3,y4,p4,r4,y5,p5,r5 = 0). It varies the orientation in each iteration and checks for the distances between matching control points (x_Img1-x_Img2, x_Img1-x_Img4, x_Img2-x_Img4, y_Img1-y_Img2, y_Img1-y_Img4, y_Img2-y_Img4) and line points (y1_Img4-y2_Img4, x3_Img4-x4_Img4). It's like a jigsaw puzzle where Hugin tries different incremental values for y p r to check if the control and line point distance is reduced or increased. The straighten button will probably not determine a dominant orientation if it is using the optimization. There is one way to search for dominant orientation as explained in section 5 of [2]. You can test the straightening process by rotating your photos. [1] SIFT or similar features https://link.springer.com/article/10.1023/B:VISI.0000029664.99615.94 [2] Panorama stitching in openCV, a bit different from Hugin https://link.springer.com/article/10.1007/s11263-006-0002-3 On Tue, May 14, 2024 at 2:59 PM 'ChameleonScales' via hugin and other free panoramic software <[email protected]> wrote: > Thank you. That answered part of my question. > I'm still wondering how it determines the orientation of the panorama > though. > > Let's say I take photos with a panoramic head at random y,p,r orientations > (so there can even be photos taken in portrait format, others in landscape > and all the in-between angles). > If I stitch them in Hugin and then click on "Straighten", will it > determine a "dominant" orientation so that the equator of the panosphere is > closest to as many photo centers as possible or will it do something else ? > > I may do some tests to understand it better. > > On Wednesday, May 8th, 2024 at 4:27 AM, David W. Jones < > [email protected]> wrote: > > On 5/6/24 23:59, 'ChameleonScales' via hugin and other free panoramic > software wrote: > > I did not make a very thoughtful assumption. Let me make a new one for > what I think it does: > > - determine a single set of pitch and roll values that is closest to > as many photos as possible > - apply the inverse of this set of values to each photo > > > Am I getting closer ? > > It's been a little more than a year. Does anyone have an answer ? > > Hmm, haven't a real clue, but maybe this will help? > > https://hugin.sourceforge.io/tutorials/two-photos/en.shtml > > Are you asking about the process behind it? The above link lists the steps > of the process the Straighten button applies. > > This link discusses the Straighten tool (at the bottom of the page): > > https://wiki.panotools.org/Hugin_move_drag_tab > > "Straightening the panorama optimises the roll > <https://wiki.panotools.org/Roll> and pitch > <https://wiki.panotools.org/Pitch> of the input images without changing > their relative positions, levelling the panorama in the process. This > normally produces good results; if you need more accurate positioning, try > adding vertical control points > <https://wiki.panotools.org/Vertical_control_points> in the Hugin Control > Points tab <https://wiki.panotools.org/Hugin_Control_Points_tab> and > reoptimise." > > Hope that helps! > > -- > David W. [email protected] > wandering the landscape of godhttp://dancingtreefrog.com > My password is the last 8 digits of π. > > -- > A list of frequently asked questions is available at: > http://wiki.panotools.org/Hugin_FAQ > --- > You received this message because you are subscribed to the Google Groups > "hugin and other free panoramic software" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/hugin-ptx/466cc222-e495-4ec9-b9e0-18e30105ec08%40gmail.com > . > > > -- > A list of frequently asked questions is available at: > http://wiki.panotools.org/Hugin_FAQ > --- > You received this message because you are subscribed to the Google Groups > "hugin and other free panoramic software" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/hugin-ptx/84aO0BheH2Obf-0CMZ3jdw4W0sZXefAdRoS0AV45tCPOnzOzU_-REcbKhvx00vBuKg2JtguamYhysRTBGlPpeUk07VNms7SImuw0l7Pt59c%3D%40protonmail.com > <https://groups.google.com/d/msgid/hugin-ptx/84aO0BheH2Obf-0CMZ3jdw4W0sZXefAdRoS0AV45tCPOnzOzU_-REcbKhvx00vBuKg2JtguamYhysRTBGlPpeUk07VNms7SImuw0l7Pt59c%3D%40protonmail.com?utm_medium=email&utm_source=footer> > . > -- A list of frequently asked questions is available at: http://wiki.panotools.org/Hugin_FAQ --- You received this message because you are subscribed to the Google Groups "hugin and other free panoramic software" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/hugin-ptx/CANh7QHxGvmvzzYdOGfkNKvmQyvu1tpKXVmqgouG-UmPNZupsQA%40mail.gmail.com.
