# Fiducial Slam with Lidar and URDF - TF issue **URL:** \ **Category:** General Questions\ **Created:** [January 27, 2020, 8:25pm UTC](https://forum.ubiquityrobotics.com/t/fiducial-slam-with-lidar-and-urdf-tf-issue/450 "2020-01-27T20:25:22Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![WayTooManyHobbies](https://forum.ubiquityrobotics.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@WayTooManyHobbies](https://forum.ubiquityrobotics.com/u/WayTooManyHobbies)\ **Post date:** [January 27, 2020, 8:25pm UTC](https://forum.ubiquityrobotics.com/t/fiducial-slam-with-lidar-and-urdf-tf-issue/450/1 "2020-01-27T20:25:22Z")
I’m doing something a little different with fiducial\_slam, specifically trying to record both fiducials and lidar scanning in the same run. I created a sensor setup that I’m pushing around on a cart - this defines a “robot” that has a pi cam and a lidar sensor. I’ve recorded a bag file with the camera images and lidar, and am trying to run fiducial\_slam on it to create the map. My URDF file defines base\_footprint -\> base\_link -\> camera, and also base\_link -\> laser frame. I am launching fiducial\_slam with the following command: roslaunch fiducial\_slam fiducial\_slam.launch map\_frame:=“map” odom\_frame:=“odom” base\_frame:=“base\_link” publish\_6dof\_pose:=“true” publish\_tf:=“true” future\_date\_transforms:=“0.5” This is giving me a separate transform tree of map -\> odom, with no connection to the “robot”. It’s also giving me a massive headache. For the life of me, I can’t get the transform tree to acknowledge that the “robot” is on the map, so fiducial\_slam can’t place anything but the initial two aruco markers. Can anyone offer some insight? I’m really at a loss. ---
**Author:** ![rohbotics](https://forum.ubiquityrobotics.com/user_avatar/forum.ubiquityrobotics.com/rohbotics/32/222_2.png) [@rohbotics](https://forum.ubiquityrobotics.com/u/rohbotics)\ **Post date:** [January 27, 2020, 11:34pm UTC](https://forum.ubiquityrobotics.com/t/fiducial-slam-with-lidar-and-urdf-tf-issue/450/2 "2020-01-27T23:34:15Z")
Hey @WayTooManyHobbies, Thanks for your question. `fiducial_slam` assums that there is some other source of odometry providing the `odom->base_link` transform. On most robots this data is provided by wheel odometry. In your case it sounds like there is nothing providing that transform, so you could a static transform publisher that published a constant 0 transform for `odom->base_link`. Note that this will mean that you will have no source of position data in between fiducial\_slam updates, which may cause issues. Rohan ---
**Author:** ![WayTooManyHobbies](https://forum.ubiquityrobotics.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@WayTooManyHobbies](https://forum.ubiquityrobotics.com/u/WayTooManyHobbies)\ **Post date:** [January 28, 2020, 10:58am UTC](https://forum.ubiquityrobotics.com/t/fiducial-slam-with-lidar-and-urdf-tf-issue/450/3 "2020-01-28T10:58:04Z")
Thanks for the information - that’s very helpful, and gives me some ideas to try. I’ll report back on how things work out. Chuck ---
**Author:** ![WayTooManyHobbies](https://forum.ubiquityrobotics.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@WayTooManyHobbies](https://forum.ubiquityrobotics.com/u/WayTooManyHobbies)\ **Post date:** [January 28, 2020, 11:33am UTC](https://forum.ubiquityrobotics.com/t/fiducial-slam-with-lidar-and-urdf-tf-issue/450/4 "2020-01-28T11:33:09Z")
OK, looks like what I wanted to do short term will not work. I’ll have to work on an odometry source and try again. Thanks for your help! ---
**Author:** ![WayTooManyHobbies](https://forum.ubiquityrobotics.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@WayTooManyHobbies](https://forum.ubiquityrobotics.com/u/WayTooManyHobbies)\ **Post date:** [January 28, 2020, 7:52pm UTC](https://forum.ubiquityrobotics.com/t/fiducial-slam-with-lidar-and-urdf-tf-issue/450/5 "2020-01-28T19:52:54Z")
I’m now trying to use slam\_toolbox in concert with the lidar to provide odometry to use with fiducial\_slam. The transforms look better, but I still don’t get the other fiducials on the map. My tf frames are shown here - anyone spot where I’m being dense? ![frames](https://frm.ubiquityrobotics.com/uploads/default/original/1X/d2723427e58063487b842a8f53c1c583e006a4d9.png) ---
**Author:** ![WayTooManyHobbies](https://forum.ubiquityrobotics.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@WayTooManyHobbies](https://forum.ubiquityrobotics.com/u/WayTooManyHobbies)\ **Post date:** [January 30, 2020, 10:14pm UTC](https://forum.ubiquityrobotics.com/t/fiducial-slam-with-lidar-and-urdf-tf-issue/450/6 "2020-01-30T22:14:30Z")
Just updating - I’m getting marginally smarter as the days go by. Finally rammed through my skull that the transform is not the same as the topic, and that I need a topic. I’m now working on another part of my project to get odometry going, and then I’ll take another stab at an integrated mapping solution with lidar-based mapping and fiducial\_slam for localization. ---
**Author:** ![johnnyv](https://forum.ubiquityrobotics.com/letter_avatar_proxy/v4/letter/j/b4bc9f/32.png) [@johnnyv](https://forum.ubiquityrobotics.com/u/johnnyv)\ **Post date:** [July 5, 2020, 1:31pm UTC](https://forum.ubiquityrobotics.com/t/fiducial-slam-with-lidar-and-urdf-tf-issue/450/7 "2020-07-05T13:31:56Z")
How did you go integrating lidar and fiducial slam?