Re: rtabmap_ros outdoor 3D mapping

Posted by acp on
URL: http://official-rtab-map-forum.206.s1.nabble.com/rtabmap-ros-outdoor-3D-mapping-tp6104p6148.html

Hi Mathew


Thank you very much for the answer. However, I have some doubts about what you have written :)

If you are using rtabmap.launch, set imu_topic argument to topic of your IMU. It can be roughly synchronized with the zed. If rtabmap node is used directly, add the remap for "imu" topic. Make sure TF between imu and the zed is accurate (at least for orientation).


     * I guess this is to give more robustness to the zed/odometer rotations, right? and  how to obtained the TF between IMU and ZED :)

     * And, why using TF if I am using rtabmap node and not using TF if I am using rtabmap.launch


Then to use the gravity constraints in the graph, add parameter "--Optimizer/GravitySigma 0.3". On loop closures, it will optimize the graph to be aligned with gravity.<quote author="matlabbe">


* What does it mean the graph to be aligned with gravity :)

The not aligned wall is a depth computation issue, the zed algorithm interpolates a lot on featureless surfaces. I think the pose is good, but the wall is very distorted. There are maybe parameters on zed side to avoid creating depth on featureless surfaces like that.


      * How can the featureless interpolation surface can cause multiple walls?

      * I have sent a mail to the stereolabs about the issue of featureless surfaces and I got the following replay:


The ZED camera uses stereo vision to estimate the depth. This technic detects details of objects in the left and right images to compare their position to estimate their depth.
Homogeneous surfaces are textureless so the depth algorithm tries to estimate them based on nearby objects. As this is less precise, the depth can vary in these areas which result in duplicated walls in your scan.

The ZED SDK has no option to filter this out but I've reported your suggestion and pictures to the development team.
I'll keep you updated if any solution gets available for testing.


Based on the previous answer, what can be done to solve that issue?


Thank you and looking forward to your replay.