Get the total contact force through the getcontactpoints command

[tianbaoloin]

Thanks for your contribution！I want to measure the total contact force during the contact of an object, I'm having some problems using the getcontactpoints command，when execute code ：LF = p.getContactPoints(robot_2leg, Platform, LFjoint3ID, JointRollID)，will return：
LF ((0, 1, 3, 3, 2, (0.3575147847445746, 0.5229021183567916, 2.074932115934242), (0.3574695221333889, 0.5228724695436423, 2.0753582418818293), (-0.10537276593447442, -0.06902335871453347, 0.9920344531068885), -0.0004295475285687035, 209.77346744866313, -15.880333100433523, (0.0, -0.9975882330978967, -0.06940977729842478), 22.44616224524268, (0.994432793203904, -0.007313900216830909, 0.10511863138521055)), (0, 1, 3, 3, 2, (0.35751384280210097, 0.5260994053402992, 2.075604540358511), (0.35752882511474693, 0.5262936809242407, 2.0756025805928253), (-0.10537276729524407, -0.0690233571296355, 0.9920344530726224), 1.6932435836144694e-05, 0.0, -0.0, (0.0, -0.9975882332080871, -0.06940977571471825), 0.0, (0.9944327930597132, -0.007313900144402089, 0.10511863275430944)))
How do I measure the total normal force？Can I get it by LF_NormalForce = LF[0][9]+LF[1][9] command？
Sometimes the command of getcontactpoints will return an array plus an empty collection，for example，
LF ((0, 1, 3, 11, 2, (0.3573315047353876, -0.5317105373239291, 1.9867967529086095), (0.3572899082631745, -0.5317492501660869, 1.9872115679195994), (-0.09934934123793521, -0.09246205654439027, 0.9907474332518708), -0.00041868895852540706, 206.0255976863918, -17.422049068103544, (0.0, -0.9956734120664479, -0.09292177626346634), 17.738783169559024, (0.9950526158930433, -0.009231717258434186, 0.0989194975769288)),)
I don't know what is the reason for this？Looking forward to your reply