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/*
-----------------------------------------------------------------------
Copyright: 2010-2021, imec Vision Lab, University of Antwerp
2014-2021, CWI, Amsterdam
Contact: astra@astra-toolbox.com
Website: http://www.astra-toolbox.com/
This file is part of the ASTRA Toolbox.
The ASTRA Toolbox is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
The ASTRA Toolbox is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with the ASTRA Toolbox. If not, see <http://www.gnu.org/licenses/>.
-----------------------------------------------------------------------
*/
#define policy_weight(p,rayindex,volindex,weight) do { if (p.pixelPrior(volindex)) { p.addWeight(rayindex, volindex, weight); p.pixelPosterior(volindex); } } while (false)
template <typename Policy>
void CParallelBeamLinearKernelProjector2D::project(Policy& p)
{
projectBlock_internal(0, m_pProjectionGeometry->getProjectionAngleCount(),
0, m_pProjectionGeometry->getDetectorCount(), p);
}
template <typename Policy>
void CParallelBeamLinearKernelProjector2D::projectSingleProjection(int _iProjection, Policy& p)
{
projectBlock_internal(_iProjection, _iProjection + 1,
0, m_pProjectionGeometry->getDetectorCount(), p);
}
template <typename Policy>
void CParallelBeamLinearKernelProjector2D::projectSingleRay(int _iProjection, int _iDetector, Policy& p)
{
projectBlock_internal(_iProjection, _iProjection + 1,
_iDetector, _iDetector + 1, p);
}
//----------------------------------------------------------------------------------------
/* PROJECT BLOCK - vector projection geometry
Kernel limitations: isotropic pixels (PixelLengthX == PixelLengthY)
For each angle/detector pair:
Let D=(Dx,Dy) denote the centre of the detector (point) in volume coordinates, and
let R=(Rx,Ry) denote the direction of the ray (vector).
For mainly vertical rays (|Rx|<=|Ry|),
let E=(Ex,Ey) denote the centre of the most upper left pixel:
E = (WindowMinX + PixelLengthX/2, WindowMaxY - PixelLengthY/2),
and let F=(Fx,Fy) denote a vector to the next pixel
F = (PixelLengthX, 0)
The intersection of the ray (D+aR) with the centre line of the upper row of pixels (E+bF) is
{ Dx + a*Rx = Ex + b*Fx
{ Dy + a*Ry = Ey + b*Fy
Solving for (a,b) results in:
a = (Ey + b*Fy - Dy)/Ry
= (Ey - Dy)/Ry
b = (Dx + a*Rx - Ex)/Fx
= (Dx + (Ey - Dy)*Rx/Ry - Ex)/Fx
Define c as the x-value of the intersection of the ray with the upper row in pixel coordinates.
c = b
The intersection of the ray (D+aR) with the centre line of the second row of pixels (E'+bF) with
E'=(WindowMinX + PixelLengthX/2, WindowMaxY - 3*PixelLengthY/2)
expressed in x-value pixel coordinates is
c' = (Dx + (Ey' - Dy)*Rx/Ry - Ex)/Fx.
And thus:
deltac = c' - c = (Dx + (Ey' - Dy)*Rx/Ry - Ex)/Fx - (Dx + (Ey - Dy)*Rx/Ry - Ex)/Fx
= [(Ey' - Dy)*Rx/Ry - (Ey - Dy)*Rx/Ry]/Fx
= [Ey' - Ey]*(Rx/Ry)/Fx
= [Ey' - Ey]*(Rx/Ry)/Fx
= -PixelLengthY*(Rx/Ry)/Fx.
Given c on a certain row, its pixel directly on its left (col), and the distance (offset) to it, can be found:
col = floor(c)
offset = c - col
The index of this pixel is
volumeIndex = row * colCount + col
The projection kernel is defined by
LengthPerRow
/|\
/ | \
__/ | \__ 0
p0 p1 p2
And thus
W_(rayIndex,volIndex) = (1 - offset) * lengthPerRow
W_(rayIndex,volIndex+1) = offset * lengthPerRow
Mainly horizontal rays (|Rx|<=|Ry|) are handled in a similar fashion:
E = (WindowMinX + PixelLengthX/2, WindowMaxY - PixelLengthY/2),
F = (0, -PixelLengthX)
a = (Ex + b*Fx - Dx)/Rx = (Ex - Dx)/Rx
b = (Dy + a*Ry - Ey)/Fy = (Dy + (Ex - Dx)*Ry/Rx - Ey)/Fy
r = b
deltar = PixelLengthX*(Ry/Rx)/Fy.
row = floor(r+1/2)
offset = r - row
LengthPerCol = pixelLengthY * sqrt(Rx^2+Ry^2) / |Rx|
W_(rayIndex,volIndex) = (1 - offset) * lengthPerCol
W_(rayIndex,volIndex+colcount) = offset * lengthPerCol
*/
template <typename Policy>
void CParallelBeamLinearKernelProjector2D::projectBlock_internal(int _iProjFrom, int _iProjTo, int _iDetFrom, int _iDetTo, Policy& p)
{
// get vector geometry
const CParallelVecProjectionGeometry2D* pVecProjectionGeometry;
if (dynamic_cast<CParallelProjectionGeometry2D*>(m_pProjectionGeometry)) {
pVecProjectionGeometry = dynamic_cast<CParallelProjectionGeometry2D*>(m_pProjectionGeometry)->toVectorGeometry();
} else {
pVecProjectionGeometry = dynamic_cast<CParallelVecProjectionGeometry2D*>(m_pProjectionGeometry);
}
// precomputations
const float32 pixelLengthX = m_pVolumeGeometry->getPixelLengthX();
const float32 pixelLengthY = m_pVolumeGeometry->getPixelLengthY();
const float32 inv_pixelLengthX = 1.0f / pixelLengthX;
const float32 inv_pixelLengthY = 1.0f / pixelLengthY;
const int colCount = m_pVolumeGeometry->getGridColCount();
const int rowCount = m_pVolumeGeometry->getGridRowCount();
// loop angles
for (int iAngle = _iProjFrom; iAngle < _iProjTo; ++iAngle) {
// variables
float32 Dx, Dy, Ex, Ey, c, r, deltac, deltar, offset;
float32 RxOverRy, RyOverRx, lengthPerRow, lengthPerCol;
int iVolumeIndex, iRayIndex, row, col, iDetector;
const SParProjection * proj = &pVecProjectionGeometry->getProjectionVectors()[iAngle];
const bool vertical = fabs(proj->fRayX) < fabs(proj->fRayY);
Ex = m_pVolumeGeometry->getWindowMinX() + pixelLengthX*0.5f;
Ey = m_pVolumeGeometry->getWindowMaxY() - pixelLengthY*0.5f;
// loop detectors
for (iDetector = _iDetFrom; iDetector < _iDetTo; ++iDetector) {
iRayIndex = iAngle * m_pProjectionGeometry->getDetectorCount() + iDetector;
// POLICY: RAY PRIOR
if (!p.rayPrior(iRayIndex)) continue;
Dx = proj->fDetSX + (iDetector+0.5f) * proj->fDetUX;
Dy = proj->fDetSY + (iDetector+0.5f) * proj->fDetUY;
bool isin = false;
// vertically
if (vertical) {
RxOverRy = proj->fRayX/proj->fRayY;
lengthPerRow = m_pVolumeGeometry->getPixelLengthX() * sqrt(proj->fRayY*proj->fRayY + proj->fRayX*proj->fRayX) / abs(proj->fRayY);
deltac = -pixelLengthY * RxOverRy * inv_pixelLengthX;
// calculate c for row 0
c = (Dx + (Ey - Dy)*RxOverRy - Ex) * inv_pixelLengthX;
// loop rows
for (row = 0; row < rowCount; ++row, c += deltac) {
col = int(floor(c));
if (col < -1 || col >= colCount) { if (!isin) continue; else break; }
offset = c - float32(col);
iVolumeIndex = row * colCount + col;
if (col >= 0) { policy_weight(p, iRayIndex, iVolumeIndex, (1.0f - offset) * lengthPerRow); }
iVolumeIndex++;
if (col + 1 < colCount) { policy_weight(p, iRayIndex, iVolumeIndex, offset * lengthPerRow); }
isin = true;
}
}
// horizontally
else {
RyOverRx = proj->fRayY/proj->fRayX;
lengthPerCol = m_pVolumeGeometry->getPixelLengthY() * sqrt(proj->fRayY*proj->fRayY + proj->fRayX*proj->fRayX) / abs(proj->fRayX);
deltar = -pixelLengthX * RyOverRx * inv_pixelLengthY;
// calculate r for col 0
r = -(Dy + (Ex - Dx)*RyOverRx - Ey) * inv_pixelLengthY;
// loop columns
for (col = 0; col < colCount; ++col, r += deltar) {
row = int(floor(r));
if (row < -1 || row >= rowCount) { if (!isin) continue; else break; }
offset = r - float32(row);
iVolumeIndex = row * colCount + col;
if (row >= 0) { policy_weight(p, iRayIndex, iVolumeIndex, (1.0f - offset) * lengthPerCol); }
iVolumeIndex += colCount;
if (row + 1 < rowCount) { policy_weight(p, iRayIndex, iVolumeIndex, offset * lengthPerCol); }
isin = true;
}
}
// POLICY: RAY POSTERIOR
p.rayPosterior(iRayIndex);
} // end loop detector
} // end loop angles
if (dynamic_cast<CParallelProjectionGeometry2D*>(m_pProjectionGeometry))
delete pVecProjectionGeometry;
}
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