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a_marker_is_partially_obscured_it_is_only_observed_by_one_camera_it_cannot_be_identified_as_being_part_of_the_wand_it_could_not_be_tracked_in_a_camera_s_image_it_was_too_close_to_a_junk_marker_to_be_identified_with_certainty_or_its_residual_value_was_too_large._point_residuals_this_is_an_average_of_all_point_residuals_in_user_distance_units_for_all_wand_markers_used_for_the_calibration._a_ray_residual_is_defined_as_the_shortest_distance_between_a_ray_and_the_calculated_location_of_the_point_assigned_to_that_ray._the_location_of_a_point_marker_center_is_computed_by_finding_the_point_that_has_the_smallest_root_mean_squared_rms_distance_to_all_rays_assigned_to_that_marker._so_this_value_is_an_indicator_of_how_closely_the_measured_ray_directions_for_all_accepted_wand_markers_intersect_and_provides_a_good_indication_of_the_accuracy_of_the_calibration._wand_residuals_the_wand_may_be_considered_to_be_a_rigid_body_having_a_much_greater_extent_than_a_single_marker._in_certain_circumstances_a_calibration_could_produce_very_low_residuals_in_every_location_where_individual_wand_markers_are_found_yet_the_connection_between_distant_markers_may_be_incorrectly_characterized_resulting_effectively_in_a_distorted_3d_space._the_wand_residual_is_the_rms_value_of_all_residuals_in_user_distance_units_obtained_when_all_markers_on_the_wand_which_is_assumed_to_be_rigid_are_simultaneously_fitted_to_their_rays_in_each_frame._its_value_will_always_be_larger_than_the_point_residual_but_it_should_not_be_much_greater._a_much_larger_wand_residual_would_indicate_that_the_distance_measurements_between_markers_further_apart_than_the_length_of_the_wand_would_probably_have_significant_errors._wand_length_sd_this_value_presents_the_standard_deviation_of_the_distance_between_the_two_outermost_markers_on_the_wand_over_all_frames_in_which_the_markers_could_be_identified._it_is_perhaps_a_better_indicator_of_the_linearity_of_the_calibrated_volume._again_the_length_units_are_user_units._it_should_be_noted_that_the_residual_values_are_a_function_of_the_accuracy_of_the_calibration_and_also_the_noise_inherent_in_the_camera_image_data._the_noise_comes_from_the_discrete_nature_of_camera_sensors_as_well_as_the_processing_electronics_and_software._using_cameras_with_low_resolution_sensors_especially_when_imaging_small_markers_can_be_a_principal_source_of_noise_and_a_major_component_of_the_presented_residual_values._here_it_should_also_be_pointed_out_that_a_calibration_with_a_smaller_number_of_frames_may_have_smaller_residual_values_than_one_with_a_large_number_of_frames_yet_the_calibration_will_usually_be_less_accurate._the_reason_is_that_it_is_easier_to_fit_the_many_camera_system_parameters_to_a_smaller_number_of_input_data_point_because_the_calibration_is_minimizing_the_overall_residuals_of_all_rays._it_biases_the_resulting_calibration_to_produce_very_low_residuals_at_the_participating_points_at_the_expense_of_locations_that_are_elsewhere_in_the_volume_where_the_residuals_may_be_quite_high._camera_list_box_this_area_provides_some_results_for_individual_cameras_as_well_as_letting_the_user_select_the_camera_whose_linearity_grid_is_to_be_displayed_in_the_main_graphics_area._rays_this_is_the_number_of_rays_from_a_camera_that_were_used_for_the_system_calibration._low_values_in_relation_to_other_cameras_indicate_that_a_camera_did_not_successfully_image_many_wand_markers_and_that_its_calibration_might_be_suspect._residual_this_value_is_the_average_residual_in_user_units_for_all_rays_that_could_be_used_from_the_camera._again_it_should_not_be_much_larger_than_for_the_other_cameras_and_it_is_somewhat_dependent_upon_the_resolution_of_the_camera_s_sensor._image_this_shows_the_approximate_percentage_of_the_camera_s_image_area_that_was_successfully_calibrated._any_marker_image_falling_outside_the_shown_grid_area_will_be_ignored_during_tracking_when_this_calibration_is_used._reference_points_box_this_list_box_provides_a_report_on_the_reference_markers_that_were_used_to_define_the_global_coordinate_system_in_which_all_marker_trajectories_will_be_expressed._point

• **% image** it usually should not be difficult to get these values above 70%. if they are less, then either the wand has not been moved sufficiently or the camera is not placed close enough to the measurement area. be aware of the fact that for a marker image to be used in one camera it must, as a minimum, also appear in at least one other camera. this factor tends to complicate the cause and effect of calibration discrepancies. to be safe it is best to collect more frames with extensive wand motions to ensure that the maximum possible coverage of the camera image areas is achieved.

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