Add params to filter out poor stereo flow matches (#1667)

* Add params to filter out poor stereo flow matches

* Added parameters: Vis/CorFlowUseMinEigenVals, Vis/CorFlowMinEigThreshold, Vis/CorFlowErrorThreshold. Renamed Stereo/GetMinEigenVals to Stereo/UseMinEigenVals

* Setting suggested default value of 20 for Vis/CorFlowErrorThreshold

---------

Co-authored-by: matlabbe <[email protected]>

corelib/include/rtabmap/core/Parameters.h

@@ -740,8 +740,11 @@ class RTABMAP_CORE_EXPORT Parameters
     RTABMAP_PARAM(Vis, CorFlowIterations,         int,   30,    uFormat("[%s=1] See cv::calcOpticalFlowPyrLK(). Used for optical flow approach.", kVisCorType().c_str()));
     RTABMAP_PARAM(Vis, CorFlowEps,                float, 0.01,  uFormat("[%s=1] See cv::calcOpticalFlowPyrLK(). Used for optical flow approach.", kVisCorType().c_str()));
     RTABMAP_PARAM(Vis, CorFlowMaxLevel,           int,   3,     uFormat("[%s=1] See cv::calcOpticalFlowPyrLK(). Used for optical flow approach.", kVisCorType().c_str()));
-    RTABMAP_PARAM(Vis, CorFlowGpu,                bool,  false, uFormat("[%s=1] Enable GPU version of the optical flow approach (only available if OpenCV is built with CUDA).", kVisCorType().c_str()));
+    RTABMAP_PARAM(Vis, CorFlowUseMinEigenVals,    bool,  true,  uFormat("[%s=1] See cv::calcOpticalFlowPyrLK(). Used for optical flow approach. Use minimum eigen values as an error measure, otherwise L1 distance between patches is used as an error measure.", kVisCorType().c_str()));
-#if defined(RTABMAP_G2O) || defined(RTABMAP_ORB_SLAM)
+    RTABMAP_PARAM(Vis, CorFlowMinEigThreshold,    float, 1e-4,  uFormat("[%s=true] If the minimum eigenvalue of a feature's spatial gradient matrix is less than this threshold, then the feature is filtered out.", kVisCorFlowUseMinEigenVals().c_str()));
+    RTABMAP_PARAM(Vis, CorFlowErrorThreshold,     float, 20,    uFormat("[%s=false] Filter out features with error greater than this threshold.", kVisCorFlowUseMinEigenVals().c_str()));
+    RTABMAP_PARAM(Vis, CorFlowGpu,                bool,  false, uFormat("[%s=1] Enable GPU version of the optical flow approach (only available if OpenCV is built with CUDA). Note that %s is not used in the GPU implementation.", kVisCorType().c_str(), kVisCorFlowUseMinEigenVals().c_str()));
+    #if defined(RTABMAP_G2O) || defined(RTABMAP_ORB_SLAM)
     RTABMAP_PARAM(Vis, BundleAdjustment,          int,   1,     "Optimization with bundle adjustment: 0=disabled, 1=g2o, 2=cvsba, 3=Ceres.");
 #else
     RTABMAP_PARAM(Vis, BundleAdjustment,          int,   0,     "Optimization with bundle adjustment: 0=disabled, 1=g2o, 2=cvsba, 3=Ceres.");
@@ -818,7 +821,10 @@ class RTABMAP_CORE_EXPORT Parameters
     RTABMAP_PARAM(Stereo, OpticalFlow,           bool, true,    "Use optical flow to find stereo correspondences, otherwise a simple block matching approach is used.");
     RTABMAP_PARAM(Stereo, SSD,                   bool, true,    uFormat("[%s=false] Use Sum of Squared Differences (SSD) window, otherwise Sum of Absolute Differences (SAD) window is used.", kStereoOpticalFlow().c_str()));
     RTABMAP_PARAM(Stereo, Eps,                   double, 0.01,  uFormat("[%s=true] Epsilon stop criterion.", kStereoOpticalFlow().c_str()));
-    RTABMAP_PARAM(Stereo, Gpu,                   bool, false,   uFormat("[%s=true] Enable GPU version of the optical flow approach (only available if OpenCV is built with CUDA).", kStereoOpticalFlow().c_str()));
+    RTABMAP_PARAM(Stereo, UseMinEigenVals,       bool, true,    uFormat("[%s=true] Use minimum eigen values as an error measure, otherwise L1 distance between patches is used as an error measure.", kStereoOpticalFlow().c_str()));
+    RTABMAP_PARAM(Stereo, MinEigThreshold,       double, 1e-4,  uFormat("[%s=true] If the minimum eigenvalue of a feature's spatial gradient matrix is less than this threshold, then the feature is filtered out.", kStereoUseMinEigenVals().c_str()));
+    RTABMAP_PARAM(Stereo, ErrorThreshold,        double, 50,    uFormat("[%s=false] Filter out features with error greater than this threshold.", kStereoUseMinEigenVals().c_str()));
+    RTABMAP_PARAM(Stereo, Gpu,                   bool, false,   uFormat("[%s=true] Enable GPU version of the optical flow approach (only available if OpenCV is built with CUDA). Note that %s is not used in the GPU implementation.", kStereoOpticalFlow().c_str(), kStereoUseMinEigenVals().c_str()));
 
     RTABMAP_PARAM(Stereo, DenseStrategy,         int, 0,  "0=cv::StereoBM, 1=cv::StereoSGBM");
 

corelib/include/rtabmap/core/RegistrationVis.h

@@ -91,6 +91,9 @@ private:
 	float _flowEps;
 	int _flowMaxLevel;
 	bool _flowGpu;
+	bool _flowUseMinEigenVals;
+	float _flowMinEigThreshold;
+	float _flowErrorThreshold;
 	float _nndr;
 	int _nnType;
 	bool _gmsWithRotation;

corelib/include/rtabmap/core/Stereo.h

@@ -96,16 +96,23 @@ public:
 #endif
 
 	float epsilon() const {return epsilon_;}
+	bool usingMinEigenVals() const {return useMinEigenVals_;}
+	float minEigThreshold() const {return minEigThreshold_;}
+	float errorThreshold() const {return errorThreshold_;}
 	virtual bool isGpuEnabled() const;
 
 private:
 	void updateStatus(
 		const std::vector<cv::Point2f> & leftCorners,
 		const std::vector<cv::Point2f> & rightCorners,
-		std::vector<unsigned char> & status) const;
+		std::vector<unsigned char> & status,
+		std::vector<float> err = {}) const;
 
 private:
 	float epsilon_;
+	bool useMinEigenVals_;
+	float minEigThreshold_;
+	float errorThreshold_;
 	bool gpu_;
 };
 

corelib/src/RegistrationVis.cpp

@@ -84,6 +84,9 @@ RegistrationVis::RegistrationVis(const ParametersMap & parameters, Registration
 		_flowEps(Parameters::defaultVisCorFlowEps()),
 		_flowMaxLevel(Parameters::defaultVisCorFlowMaxLevel()),
 		_flowGpu(Parameters::defaultVisCorFlowGpu()),
+		_flowUseMinEigenVals(Parameters::defaultVisCorFlowUseMinEigenVals()),
+		_flowMinEigThreshold(Parameters::defaultVisCorFlowMinEigThreshold()),
+		_flowErrorThreshold(Parameters::defaultVisCorFlowErrorThreshold()),
 		_nndr(Parameters::defaultVisCorNNDR()),
 		_nnType(Parameters::defaultVisCorNNType()),
 		_gmsWithRotation(Parameters::defaultGMSWithRotation()),
@@ -145,6 +148,9 @@ void RegistrationVis::parseParameters(const ParametersMap & parameters)
 	Parameters::parse(parameters, Parameters::kVisCorFlowEps(), _flowEps);
 	Parameters::parse(parameters, Parameters::kVisCorFlowMaxLevel(), _flowMaxLevel);
 	Parameters::parse(parameters, Parameters::kVisCorFlowGpu(), _flowGpu);
+	Parameters::parse(parameters, Parameters::kVisCorFlowUseMinEigenVals(), _flowUseMinEigenVals);
+	Parameters::parse(parameters, Parameters::kVisCorFlowMinEigThreshold(), _flowMinEigThreshold);
+	Parameters::parse(parameters, Parameters::kVisCorFlowErrorThreshold(), _flowErrorThreshold);
 	Parameters::parse(parameters, Parameters::kVisCorNNDR(), _nndr);
 	Parameters::parse(parameters, Parameters::kVisCorNNType(), _nnType);
 	Parameters::parse(parameters, Parameters::kGMSWithRotation(), _gmsWithRotation);
@@ -656,6 +662,7 @@ Transform RegistrationVis::computeTransformationImpl(
 				// Find features in the new left image
 				UDEBUG("guessSet = %d", guessSet?1:0);
 				std::vector<unsigned char> status;
+				std::vector<float> err;
 #ifdef HAVE_OPENCV_CUDAOPTFLOW
 				if (_flowGpu)
 				{
@@ -685,7 +692,6 @@ Transform RegistrationVis::computeTransformationImpl(
 				else
 #endif
 				{
-					std::vector<float> err;
 					UDEBUG("cv::calcOpticalFlowPyrLK() begin");
 					cv::calcOpticalFlowPyrLK(
 						imageFrom,
@@ -697,7 +703,8 @@ Transform RegistrationVis::computeTransformationImpl(
 						cv::Size(_flowWinSize, _flowWinSize),
 						guessSet ? 0 : _flowMaxLevel,
 						cv::TermCriteria(cv::TermCriteria::COUNT + cv::TermCriteria::EPS, _flowIterations, _flowEps),
-						cv::OPTFLOW_LK_GET_MIN_EIGENVALS | (guessSet ? cv::OPTFLOW_USE_INITIAL_FLOW : 0), 1e-4);
+						(_flowUseMinEigenVals ? cv::OPTFLOW_LK_GET_MIN_EIGENVALS : 0) | (guessSet ? cv::OPTFLOW_USE_INITIAL_FLOW : 0),
+						_flowMinEigThreshold);
 					UDEBUG("cv::calcOpticalFlowPyrLK() end");
 				}
 
@@ -706,11 +713,14 @@ Transform RegistrationVis::computeTransformationImpl(
 				std::vector<cv::Point3f> kptsFrom3DKept(kptsFrom3D.size());
 				std::vector<int> orignalWordsFromIdsCpy = orignalWordsFromIds;
 				int ki = 0;
+				UASSERT((status.empty() || cornersTo.size() == status.size()) &&
+						(err.empty() || cornersTo.size() == err.size()));
 				for(unsigned int i=0; i<status.size(); ++i)
 				{
 					if(status[i] &&
 					   uIsInBounds(cornersTo[i].x, 0.0f, float(imageTo.cols)) &&
-					   uIsInBounds(cornersTo[i].y, 0.0f, float(imageTo.rows)))
+					   uIsInBounds(cornersTo[i].y, 0.0f, float(imageTo.rows)) &&
+					   (_flowUseMinEigenVals || err.empty() || err[i] < _flowErrorThreshold))
 					{
 						if(orignalWordsFromIdsCpy.size())
 						{

corelib/src/Stereo.cpp

@@ -113,6 +113,9 @@ std::vector<cv::Point2f> Stereo::computeCorrespondences(
 StereoOpticalFlow::StereoOpticalFlow(const ParametersMap & parameters) :
 		Stereo(parameters),
 		epsilon_(Parameters::defaultStereoEps()),
+		useMinEigenVals_(Parameters::defaultStereoUseMinEigenVals()),
+		minEigThreshold_(Parameters::defaultStereoMinEigThreshold()),
+		errorThreshold_(Parameters::defaultStereoErrorThreshold()),
 		gpu_(Parameters::defaultStereoGpu())
 {
 	this->parseParameters(parameters);
@@ -122,6 +125,9 @@ void StereoOpticalFlow::parseParameters(const ParametersMap & parameters)
 {
 	Stereo::parseParameters(parameters);
 	Parameters::parse(parameters, Parameters::kStereoEps(), epsilon_);
+	Parameters::parse(parameters, Parameters::kStereoUseMinEigenVals(), useMinEigenVals_);
+	Parameters::parse(parameters, Parameters::kStereoMinEigThreshold(), minEigThreshold_);
+	Parameters::parse(parameters, Parameters::kStereoErrorThreshold(), errorThreshold_);
 	Parameters::parse(parameters, Parameters::kStereoGpu(), gpu_);
 #ifndef HAVE_OPENCV_CUDAOPTFLOW
 	if(gpu_)
@@ -171,11 +177,18 @@ std::vector<cv::Point2f> StereoOpticalFlow::computeCorrespondences(
 				err,
 				this->winSize(),
 				this->maxLevel(),
-				cv::TermCriteria(cv::TermCriteria::COUNT+cv::TermCriteria::EPS, this->iterations(), epsilon_),
+				cv::TermCriteria(cv::TermCriteria::COUNT+cv::TermCriteria::EPS, this->iterations(), this->epsilon()),
-				cv::OPTFLOW_LK_GET_MIN_EIGENVALS, 1e-4);
+				this->usingMinEigenVals() ? cv::OPTFLOW_LK_GET_MIN_EIGENVALS : 0, this->minEigThreshold());
 		UDEBUG("util2d::calcOpticalFlowPyrLKStereo() end");
 	}
-	updateStatus(leftCorners, rightCorners, status);
+	if(this->usingMinEigenVals())
+	{
+		updateStatus(leftCorners, rightCorners, status);
+	}
+	else
+	{
+		updateStatus(leftCorners, rightCorners, status, err);
+	}
 	return rightCorners;
 }
 
@@ -227,14 +240,17 @@ std::vector<cv::Point2f> StereoOpticalFlow::computeCorrespondences(
 void StereoOpticalFlow::updateStatus(
 		const std::vector<cv::Point2f> & leftCorners,
 		const std::vector<cv::Point2f> & rightCorners,
-		std::vector<unsigned char> & status) const
+		std::vector<unsigned char> & status,
+		std::vector<float> err) const
 {
-	UASSERT(leftCorners.size() == rightCorners.size() && status.size() == leftCorners.size());
+	UASSERT(
+		leftCorners.size() == rightCorners.size() && status.size() == leftCorners.size() &&
+		(err.empty() || err.size() == leftCorners.size()));
 	int countFlowRejected = 0;
 	int countDisparityRejected = 0;
 	for(unsigned int i=0; i<status.size(); ++i)
 	{
-		if(status[i]!=0)
+		if(status[i]!=0 && (err.empty() || err[i] < this->errorThreshold()))
 		{
 			float disparity = leftCorners[i].x - rightCorners[i].x;
 			if(disparity <= this->minDisparity() || disparity > this->maxDisparity())

guilib/src/PreferencesDialog.cpp

@@ -1358,6 +1358,9 @@ PreferencesDialog::PreferencesDialog(QWidget * parent) :
 	_ui->odom_flow_iterations->setObjectName(Parameters::kVisCorFlowIterations().c_str());
 	_ui->odom_flow_eps->setObjectName(Parameters::kVisCorFlowEps().c_str());
 	_ui->odom_flow_gpu->setObjectName(Parameters::kVisCorFlowGpu().c_str());
+	_ui->odom_flow_useMinEigenVals->setObjectName(Parameters::kVisCorFlowUseMinEigenVals().c_str());
+	_ui->odom_flow_minEigThreshold->setObjectName(Parameters::kVisCorFlowMinEigThreshold().c_str());
+	_ui->odom_flow_errorThreshold->setObjectName(Parameters::kVisCorFlowErrorThreshold().c_str());
 	_ui->loopClosure_bundle->setObjectName(Parameters::kVisBundleAdjustment().c_str());
 
 	//RegistrationIcp
@@ -1678,6 +1681,9 @@ PreferencesDialog::PreferencesDialog(QWidget * parent) :
 	_ui->stereo_maxDisparity->setObjectName(Parameters::kStereoMaxDisparity().c_str());
 	_ui->stereo_ssd->setObjectName(Parameters::kStereoSSD().c_str());
 	_ui->stereo_flow_eps->setObjectName(Parameters::kStereoEps().c_str());
+	_ui->stereo_flow_useMinEigenVals->setObjectName(Parameters::kStereoUseMinEigenVals().c_str());
+	_ui->stereo_flow_minEigThreshold->setObjectName(Parameters::kStereoMinEigThreshold().c_str());
+	_ui->stereo_flow_errorThreshold->setObjectName(Parameters::kStereoErrorThreshold().c_str());
 	_ui->stereo_opticalFlow->setObjectName(Parameters::kStereoOpticalFlow().c_str());
 	_ui->stereo_flow_gpu->setObjectName(Parameters::kStereoGpu().c_str());
 

guilib/src/ui/preferencesDialog.ui

@@ -95,7 +95,7 @@
                 <enum>QFrame::Raised</enum>
                </property>
                <property name="currentIndex">
-                <number>10</number>
+                <number>24</number>
                </property>
                <widget class="QWidget" name="page_22">
                 <layout class="QVBoxLayout" name="verticalLayout_29" stretch="0,0">
@@ -16425,7 +16425,7 @@ If set to false, classic RTAB-Map loop closure detection is done using only imag
                     <item>
                      <widget class="QStackedWidget" name="stackedWidget_odometryType">
                       <property name="currentIndex">
-                       <number>13</number>
+                       <number>1</number>
                       </property>
                       <widget class="QWidget" name="page_52">
                        <layout class="QVBoxLayout" name="verticalLayout_77">
@@ -16965,6 +16965,22 @@ If set to false, classic RTAB-Map loop closure detection is done using only imag
                               <string>[Visual] Correspondences computation: Optical Flow</string>
                              </property>
                              <layout class="QGridLayout" name="gridLayout_52" columnstretch="0,1">
+                              <item row="0" column="0">
+                               <widget class="QSpinBox" name="odom_flow_winSize">
+                                <property name="minimum">
+                                 <number>1</number>
+                                </property>
+                                <property name="maximum">
+                                 <number>999999</number>
+                                </property>
+                                <property name="singleStep">
+                                 <number>1</number>
+                                </property>
+                                <property name="value">
+                                 <number>21</number>
+                                </property>
+                               </widget>
+                              </item>
                               <item row="0" column="1">
                                <widget class="QLabel" name="label_201">
                                 <property name="text">
@@ -16978,19 +16994,6 @@ If set to false, classic RTAB-Map loop closure detection is done using only imag
                                 </property>
                                </widget>
                               </item>
-                              <item row="3" column="1">
-                               <widget class="QLabel" name="label_297">
-                                <property name="text">
-                                 <string>Max level.</string>
-                                </property>
-                                <property name="wordWrap">
-                                 <bool>true</bool>
-                                </property>
-                                <property name="textInteractionFlags">
-                                 <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
-                                </property>
-                               </widget>
-                              </item>
                               <item row="1" column="0">
                                <widget class="QSpinBox" name="odom_flow_iterations">
                                 <property name="minimum">
@@ -17007,19 +17010,16 @@ If set to false, classic RTAB-Map loop closure detection is done using only imag
                                 </property>
                                </widget>
                               </item>
-                              <item row="0" column="0">
+                              <item row="1" column="1">
-                               <widget class="QSpinBox" name="odom_flow_winSize">
+                               <widget class="QLabel" name="label_295">
-                                <property name="minimum">
+                                <property name="text">
-                                 <number>1</number>
+                                 <string>Iterations.</string>
                                 </property>
-                                <property name="maximum">
+                                <property name="wordWrap">
-                                 <number>999999</number>
+                                 <bool>true</bool>
                                 </property>
-                                <property name="singleStep">
+                                <property name="textInteractionFlags">
-                                 <number>1</number>
+                                 <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
-                                </property>
-                                <property name="value">
-                                 <number>21</number>
                                 </property>
                                </widget>
                               </item>
@@ -17042,10 +17042,10 @@ If set to false, classic RTAB-Map loop closure detection is done using only imag
                                 </property>
                                </widget>
                               </item>
-                              <item row="1" column="1">
+                              <item row="2" column="1">
-                               <widget class="QLabel" name="label_295">
+                               <widget class="QLabel" name="label_296">
                                 <property name="text">
-                                 <string>Iterations.</string>
+                                 <string>Epsilon.</string>
                                 </property>
                                 <property name="wordWrap">
                                  <bool>true</bool>
@@ -17071,23 +17071,10 @@ If set to false, classic RTAB-Map loop closure detection is done using only imag
                                 </property>
                                </widget>
                               </item>
-                              <item row="2" column="1">
+                              <item row="3" column="1">
-                               <widget class="QLabel" name="label_296">
+                               <widget class="QLabel" name="label_297">
                                 <property name="text">
-                                 <string>Epsilon.</string>
+                                 <string>Max level.</string>
-                                </property>
-                                <property name="wordWrap">
-                                 <bool>true</bool>
-                                </property>
-                                <property name="textInteractionFlags">
-                                 <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
-                                </property>
-                               </widget>
-                              </item>
-                              <item row="4" column="1">
-                               <widget class="QLabel" name="label_odom_flow_gpu">
-                                <property name="text">
-                                 <string>Use GPU. OpenCV built with CUDA required.</string>
                                 </property>
                                 <property name="wordWrap">
                                  <bool>true</bool>
@@ -17098,12 +17085,109 @@ If set to false, classic RTAB-Map loop closure detection is done using only imag
                                </widget>
                               </item>
                               <item row="4" column="0">
+                               <widget class="QCheckBox" name="odom_flow_useMinEigenVals">
+                                <property name="text">
+                                 <string/>
+                                </property>
+                               </widget>
+                              </item>
+                              <item row="4" column="1">
+                               <widget class="QLabel" name="label_792">
+                                <property name="text">
+                                 <string>Use minimum eigen values as an error measure, otherwise L1 distance between patches is used as an error measure.</string>
+                                </property>
+                                <property name="wordWrap">
+                                 <bool>true</bool>
+                                </property>
+                                <property name="textInteractionFlags">
+                                 <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
+                                </property>
+                               </widget>
+                              </item>
+                              <item row="5" column="0">
+                               <widget class="QDoubleSpinBox" name="odom_flow_minEigThreshold">
+                                <property name="decimals">
+                                 <number>6</number>
+                                </property>
+                                <property name="minimum">
+                                 <double>0.000000000000000</double>
+                                </property>
+                                <property name="maximum">
+                                 <double>1.000000000000000</double>
+                                </property>
+                                <property name="singleStep">
+                                 <double>0.000100000000000</double>
+                                </property>
+                                <property name="value">
+                                 <double>0.000100000000000</double>
+                                </property>
+                               </widget>
+                              </item>
+                              <item row="5" column="1">
+                               <widget class="QLabel" name="label_791">
+                                <property name="text">
+                                 <string>[Eigen error measure] If the minimum eigenvalue of a feature's spatial gradient matrix is less than this threshold, then the feature is filtered out.</string>
+                                </property>
+                                <property name="wordWrap">
+                                 <bool>true</bool>
+                                </property>
+                                <property name="textInteractionFlags">
+                                 <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
+                                </property>
+                               </widget>
+                              </item>
+                              <item row="6" column="0">
+                               <widget class="QDoubleSpinBox" name="odom_flow_errorThreshold">
+                                <property name="decimals">
+                                 <number>6</number>
+                                </property>
+                                <property name="minimum">
+                                 <double>0.000000000000000</double>
+                                </property>
+                                <property name="maximum">
+                                 <double>9999.000000000000000</double>
+                                </property>
+                                <property name="singleStep">
+                                 <double>1.000000000000000</double>
+                                </property>
+                                <property name="value">
+                                 <double>50.000000000000000</double>
+                                </property>
+                               </widget>
+                              </item>
+                              <item row="6" column="1">
+                               <widget class="QLabel" name="label_793">
+                                <property name="text">
+                                 <string>[L1 error measure] Filter out features with error greater than this threshold.</string>
+                                </property>
+                                <property name="wordWrap">
+                                 <bool>true</bool>
+                                </property>
+                                <property name="textInteractionFlags">
+                                 <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
+                                </property>
+                               </widget>
+                              </item>
+                              <item row="7" column="0">
                                <widget class="QCheckBox" name="odom_flow_gpu">
                                 <property name="text">
                                  <string/>
                                 </property>
                                </widget>
                               </item>
+                              <item row="7" column="1">
+                               <widget class="QLabel" name="label_odom_flow_gpu">
+                                <property name="text">
+                                 <string>Use GPU. OpenCV built with CUDA required.  Note that the error measure parameter is not used with the GPU implementation.</string>
+                                </property>
+                                <property name="wordWrap">
+                                 <bool>true</bool>
+                                </property>
+                                <property name="textInteractionFlags">
+                                 <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
+                                </property>
+                               </widget>
+                              </item>
                              </layout>
                             </widget>
                            </item>
@@ -23020,6 +23104,35 @@ Lower the ratio -&gt; higher the precision.</string>
                            <string>Motion estimation: 3D to 3D</string>
                           </property>
                           <layout class="QGridLayout" name="gridLayout_6" columnstretch="0,1">
+                           <item row="1" column="1">
+                            <widget class="QLabel" name="label_38">
+                             <property name="text">
+                              <string>Refine iterations of the resulting transformation computed by RANSAC. 0 means no refining.</string>
+                             </property>
+                             <property name="wordWrap">
+                              <bool>true</bool>
+                             </property>
+                             <property name="textInteractionFlags">
+                              <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
+                             </property>
+                            </widget>
+                           </item>
+                           <item row="1" column="0">
+                            <widget class="QSpinBox" name="loopClosure_bowRefineIterations">
+                             <property name="minimum">
+                              <number>0</number>
+                             </property>
+                             <property name="maximum">
+                              <number>10000</number>
+                             </property>
+                             <property name="singleStep">
+                              <number>1</number>
+                             </property>
+                             <property name="value">
+                              <number>10</number>
+                             </property>
+                            </widget>
+                           </item>
                            <item row="0" column="0">
                             <widget class="QDoubleSpinBox" name="loopClosure_bowInlierDistance">
                              <property name="suffix">
@@ -23052,34 +23165,18 @@ Lower the ratio -&gt; higher the precision.</string>
                              </property>
                             </widget>
                            </item>
-                           <item row="1" column="0">
+                           <item row="2" column="1">
-                            <widget class="QSpinBox" name="loopClosure_bowRefineIterations">
+                            <spacer name="verticalSpacer_93">
-                             <property name="minimum">
+                             <property name="orientation">
-                              <number>0</number>
+                              <enum>Qt::Vertical</enum>
                              </property>
-                             <property name="maximum">
+                             <property name="sizeHint" stdset="0">
-                              <number>10000</number>
+                              <size>
+                               <width>20</width>
+                               <height>40</height>
+                              </size>
                              </property>
-                             <property name="singleStep">
+                            </spacer>
-                              <number>1</number>
-                             </property>
-                             <property name="value">
-                              <number>10</number>
-                             </property>
-                            </widget>
-                           </item>
-                           <item row="1" column="1">
-                            <widget class="QLabel" name="label_38">
-                             <property name="text">
-                              <string>Refine iterations of the resulting transformation computed by RANSAC. 0 means no refining.</string>
-                             </property>
-                             <property name="wordWrap">
-                              <bool>true</bool>
-                             </property>
-                             <property name="textInteractionFlags">
-                              <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
-                             </property>
-                            </widget>
                            </item>
                           </layout>
                          </widget>
@@ -24566,7 +24663,7 @@ Lower the ratio -&gt; higher the precision.</string>
                     <item>
                      <widget class="QStackedWidget" name="stackedWidget_icpStrategy">
                       <property name="currentIndex">
-                       <number>2</number>
+                       <number>0</number>
                       </property>
                       <widget class="QWidget" name="page_90">
                        <layout class="QVBoxLayout" name="verticalLayout_156">
@@ -25532,10 +25629,17 @@ Lower the ratio -&gt; higher the precision.</string>
                          </property>
                         </widget>
                        </item>
-                       <item row="10" column="1">
+                       <item row="10" column="0">
-                        <widget class="QLabel" name="label_stereo_flow_gpu">
+                        <widget class="QCheckBox" name="stereo_flow_useMinEigenVals">
                          <property name="text">
-                          <string>[OpticalFlow = true] Do optical flow on GPU. RTAB-Map should be built with OpenCV CUDA.</string>
+                          <string/>
+                         </property>
+                        </widget>
+                       </item>
+                       <item row="10" column="1">
+                        <widget class="QLabel" name="label_788">
+                         <property name="text">
+                          <string>[OpticalFlow = true] Use minimum eigen values as an error measure, otherwise L1 distance between patches is used as an error measure.</string>
                          </property>
                          <property name="wordWrap">
                           <bool>true</bool>
@@ -25545,13 +25649,90 @@ Lower the ratio -&gt; higher the precision.</string>
                          </property>
                         </widget>
                        </item>
-                       <item row="10" column="0">
+                       <item row="11" column="0">
+                        <widget class="QDoubleSpinBox" name="stereo_flow_minEigThreshold">
+                         <property name="decimals">
+                          <number>6</number>
+                         </property>
+                         <property name="minimum">
+                          <double>0.000000000000000</double>
+                         </property>
+                         <property name="maximum">
+                          <double>1.000000000000000</double>
+                         </property>
+                         <property name="singleStep">
+                          <double>0.000100000000000</double>
+                         </property>
+                         <property name="value">
+                          <double>0.000100000000000</double>
+                         </property>
+                        </widget>
+                       </item>
+                       <item row="11" column="1">
+                        <widget class="QLabel" name="label_789">
+                         <property name="text">
+                          <string>[OpticalFlow = true / Eigen error measure] If the minimum eigenvalue of a feature's spatial gradient matrix is less than this threshold, then the feature is filtered out.</string>
+                         </property>
+                         <property name="wordWrap">
+                          <bool>true</bool>
+                         </property>
+                         <property name="textInteractionFlags">
+                          <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
+                         </property>
+                        </widget>
+                       </item>
+                       <item row="12" column="0">
+                        <widget class="QDoubleSpinBox" name="stereo_flow_errorThreshold">
+                         <property name="decimals">
+                          <number>6</number>
+                         </property>
+                         <property name="minimum">
+                          <double>0.000000000000000</double>
+                         </property>
+                         <property name="maximum">
+                          <double>9999.000000000000000</double>
+                         </property>
+                         <property name="singleStep">
+                          <double>1.000000000000000</double>
+                         </property>
+                         <property name="value">
+                          <double>50.000000000000000</double>
+                         </property>
+                        </widget>
+                       </item>
+                       <item row="12" column="1">
+                        <widget class="QLabel" name="label_790">
+                         <property name="text">
+                          <string>[OpticalFlow = true / L1 error measure] Filter out features with error greater than this threshold.</string>
+                         </property>
+                         <property name="wordWrap">
+                          <bool>true</bool>
+                         </property>
+                         <property name="textInteractionFlags">
+                          <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
+                         </property>
+                        </widget>
+                       </item>
+                       <item row="13" column="0">
                         <widget class="QCheckBox" name="stereo_flow_gpu">
                          <property name="text">
                           <string/>
                          </property>
                         </widget>
                        </item>
+                       <item row="13" column="1">
+                        <widget class="QLabel" name="label_stereo_flow_gpu">
+                         <property name="text">
+                          <string>[OpticalFlow = true] Do optical flow on GPU. RTAB-Map should be built with OpenCV CUDA. Note that the error measure parameter is not used with the GPU implementation.</string>
+                         </property>
+                         <property name="wordWrap">
+                          <bool>true</bool>
+                         </property>
+                         <property name="textInteractionFlags">
+                          <set>Qt::LinksAccessibleByMouse|Qt::TextSelectableByMouse</set>
+                         </property>
+                        </widget>
+                       </item>
                       </layout>
                      </widget>
                     </item>