open-discussion
open-discussion > RE: Problem with SPHARM-PDM on new dataset!
Nov 10, 2016 06:11 PM | Martin Styner
RE: Problem with SPHARM-PDM on new dataset!
Hi Nazanin
The idea behind normal projection is that the established correspondence is imperfect and one wants to neglect the part of the difference between surfaces that is along the surface itself. One may not want to include measure shape differences that are due to a surface location 'sliding' along the surface but the surface itself is not different. Rather, one may only be interested in that shape change part that goes purely inwards or outwards. That's what the normal projection does, i.e. computing that pure inwards/outwards shape difference.
Not sure I fully understand your second question. The phi and theta at the same point index should indeed be the same across subjects. Though that is only true after the SPHARM fit (i.e. not the original para surfaces, which are the spherical parametrization of the original surfaces, which do not have correspondence nor even the same number of points.
Martin
Originally posted by Nazanin M:
The idea behind normal projection is that the established correspondence is imperfect and one wants to neglect the part of the difference between surfaces that is along the surface itself. One may not want to include measure shape differences that are due to a surface location 'sliding' along the surface but the surface itself is not different. Rather, one may only be interested in that shape change part that goes purely inwards or outwards. That's what the normal projection does, i.e. computing that pure inwards/outwards shape difference.
Not sure I fully understand your second question. The phi and theta at the same point index should indeed be the same across subjects. Though that is only true after the SPHARM fit (i.e. not the original para surfaces, which are the spherical parametrization of the original surfaces, which do not have correspondence nor even the same number of points.
Martin
Originally posted by Nazanin M:
This completely makes sense.
Now may I ask why you chose the projection of the difference vector on the mean surface normal? I know that we can get the signed value, but doing the projection aren't we losing some distance? Does it make sense if I get the difference vector's magnitude multiplied by the sign of the result of projection on mean vector? Again, what does projection give us aside from the sign?
The other thing that I am confused about so much is that why doesn't the properties of point 1 in sample1 correspond to point 1 in sample2? They have different theta, phi, and R. I was expecting to get similar theta, and phi for point x across all subjects, where only the R changes...
Again, thank you so much for the effort and time you put for answering questions on the forum.
Nazanin
Now may I ask why you chose the projection of the difference vector on the mean surface normal? I know that we can get the signed value, but doing the projection aren't we losing some distance? Does it make sense if I get the difference vector's magnitude multiplied by the sign of the result of projection on mean vector? Again, what does projection give us aside from the sign?
The other thing that I am confused about so much is that why doesn't the properties of point 1 in sample1 correspond to point 1 in sample2? They have different theta, phi, and R. I was expecting to get similar theta, and phi for point x across all subjects, where only the R changes...
Again, thank you so much for the effort and time you put for answering questions on the forum.
Nazanin
Threaded View
| Title | Author | Date |
|---|---|---|
| Nazanin M | Sep 27, 2016 | |
| Nazanin M | Nov 4, 2016 | |
| Martin Styner | Nov 10, 2016 | |
| Nazanin M | Dec 26, 2016 | |
| Martin Styner | Jan 2, 2017 | |
| Nazanin M | Jan 2, 2017 | |
| Martin Styner | Jan 5, 2017 | |
| Nazanin M | Jan 11, 2017 | |
| Martin Styner | Jan 17, 2017 | |
| Nazanin M | Jan 17, 2017 | |
| Nazanin M | Jan 17, 2017 | |
| Nazanin M | Nov 2, 2016 | |
| Martin Styner | Nov 4, 2016 | |
| Antoine Bouyeure | Oct 30, 2016 | |
| Martin Styner | Oct 31, 2016 | |
| D J | Nov 1, 2016 | |
| Antoine Bouyeure | Nov 1, 2016 | |
| Martin Styner | Nov 1, 2016 | |
| Antoine Bouyeure | Oct 29, 2016 | |
| Nazanin M | Oct 30, 2016 | |
| Martin Styner | Oct 31, 2016 | |