From 9887d586325113d4a54e1f52fcc27d483b88345d Mon Sep 17 00:00:00 2001
From: "se.gorbunov" <se.gorbunov@gsi.de>
Date: Tue, 22 Aug 2023 22:58:17 +0000
Subject: [PATCH] sts hithinder: fix rotation of the hit covariance matrix
---
core/base/utils/CbmGeometryUtils.cxx | 27 +++++++++++++++++++++++
core/base/utils/CbmGeometryUtils.h | 10 +++++++++
reco/detectors/sts/CbmStsAlgoFindHits.cxx | 11 ++++-----
3 files changed, 43 insertions(+), 5 deletions(-)
diff --git a/core/base/utils/CbmGeometryUtils.cxx b/core/base/utils/CbmGeometryUtils.cxx
index 41480c686e..5701b38c22 100644
--- a/core/base/utils/CbmGeometryUtils.cxx
+++ b/core/base/utils/CbmGeometryUtils.cxx
@@ -322,5 +322,32 @@ namespace Cbm
}
+ void LocalToMasterCovarianceMatrix(const TGeoMatrix& m, Double_t& covXX, Double_t& covXY, Double_t& covYY)
+ {
+ // Fast calculation with skipping zeros
+
+ // 3x3 covariance matrix. c01==c11, other elements are 0.
+ double c00 = covXX;
+ double c10 = covXY;
+ double c11 = covYY;
+
+ // 3x3 transformation matrix. other elements will not be needed
+ double r00 = m.GetRotationMatrix()[0];
+ double r01 = m.GetRotationMatrix()[1];
+ double r10 = m.GetRotationMatrix()[3];
+ double r11 = m.GetRotationMatrix()[4];
+
+ // rc == r * c
+ double rc00 = r00 * c00 + r01 * c10;
+ double rc01 = r00 * c10 + r01 * c11;
+ double rc10 = r10 * c00 + r11 * c10;
+ double rc11 = r10 * c10 + r11 * c11;
+
+ // transformed c = rc * r^t
+ covXX = rc00 * r00 + rc01 * r01;
+ covXY = rc10 * r00 + rc11 * r01;
+ covYY = rc10 * r10 + rc11 * r11;
+ }
+
} // namespace GeometryUtils
} // namespace Cbm
diff --git a/core/base/utils/CbmGeometryUtils.h b/core/base/utils/CbmGeometryUtils.h
index 401e189fbf..72b304c9c3 100644
--- a/core/base/utils/CbmGeometryUtils.h
+++ b/core/base/utils/CbmGeometryUtils.h
@@ -2,6 +2,8 @@
SPDX-License-Identifier: GPL-3.0-only
Authors: Florian Uhlig [committer] */
+#include "Rtypes.h"
+
class TGeoMatrix;
class TGeoVolume;
class FairModule;
@@ -24,5 +26,13 @@ namespace Cbm
void AssignMediumAtImport(TGeoVolume* v);
void ExpandNodes(TGeoVolume* volume, FairModule* mod);
+
+ /// @brief Convert the local X/Y covariance matrix to global coordinates
+ /// @param m the transformation matrix
+ /// @param covXX covariance X,X
+ /// @param covXY covariance X,Y
+ /// @param covYY covariance Y,Y
+ void LocalToMasterCovarianceMatrix(const TGeoMatrix& m, Double_t& covXX, Double_t& covXY, Double_t& covYY);
+
} // namespace GeometryUtils
} // namespace Cbm
diff --git a/reco/detectors/sts/CbmStsAlgoFindHits.cxx b/reco/detectors/sts/CbmStsAlgoFindHits.cxx
index 5f2634b96f..1d8cd6ef49 100644
--- a/reco/detectors/sts/CbmStsAlgoFindHits.cxx
+++ b/reco/detectors/sts/CbmStsAlgoFindHits.cxx
@@ -9,6 +9,7 @@
#include "CbmStsAlgoFindHits.h"
#include "CbmDigiManager.h"
+#include "CbmGeometryUtils.h"
#include "CbmStsCluster.h"
#include "CbmStsDigi.h"
#include "CbmStsHit.h"
@@ -40,17 +41,17 @@ void CbmStsAlgoFindHits::CreateHit(Double_t xLocal, Double_t yLocal, Double_t va
// --- Transform into global coordinate system
Double_t local[3] = {xLocal, yLocal, 0.};
Double_t global[3];
- if (fMatrix) fMatrix->LocalToMaster(local, global);
+
+ if (fMatrix) {
+ fMatrix->LocalToMaster(local, global);
+ Cbm::GeometryUtils::LocalToMasterCovarianceMatrix(*fMatrix, varX, varXY, varY);
+ }
else {
global[0] = local[0];
global[1] = local[1];
global[2] = local[2];
} //? no transformation matrix available
- // We assume here that the local-to-global transformations is only translation
- // plus maybe rotation upside down or front-side back. In that case, the
- // global covariance matrix is the same as the local one.
- // TODO: Proper transformation of covariance matrix
Double_t error[3] = {TMath::Sqrt(varX), TMath::Sqrt(varY), 0.};
// --- Calculate hit time (average of cluster times)
--
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