# April tag detection non- existent with errors

**URL:** <https://forum.theavr.org/t/april-tag-detection-non-existent-with-errors/760>\
**Category:** AVR Drone Software\
**Created:** [November 15, 2023, 2:50am UTC](https://forum.theavr.org/t/april-tag-detection-non-existent-with-errors/760 "2023-11-15T02:50:08Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![5A5UK3](https://avatars.discourse-cdn.com/v4/letter/5/48db29/32.png) [@5A5UK3](https://forum.theavr.org/u/5A5UK3)\
**Post date:** [November 15, 2023, 2:50am UTC](https://forum.theavr.org/t/april-tag-detection-non-existent-with-errors/760/1 "2023-11-15T02:50:08Z")

</div>

Hey,

we were trying to set up April pad detection on our AVR drone. In the process of doing so, we ran into multiple errors. We have tried flipping the cable (using both sides), different jetson development boards, different cameras, and cables. The only constant in our problem is the code we are running(attached code block). Any suggestions on how to fix this?

```auto
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/libnvparsers.so.8.0.1 is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/libnvinfer_plugin.so.8.0.1 is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/libnvinfer.so.8.0.1 is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/libnvonnxparser.so.8.0.1 is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/tegra/libnvidia-eglcore.so.32.6.1 is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/tegra/libnvidia-rmapi-tegra.so.32.6.1 is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/tegra/libnvisp_utils.so is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/tegra/libnvidia-glcore.so.32.6.1 is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/tegra/libnvidia-glsi.so.32.6.1 is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/tegra/libnvidia-glvkspirv.so.32.6.1 is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/tegra/libnvidia-tls.so.32.6.1 is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/tegra/libnvpva.so is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/tegra/libnvcuvidv4l2.so is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/tegra/libv4l2_nvcuvidvideocodec.so is empty, not checked.
/sbin/ldconfig.real: File /usr/lib/aarch64-linux-gnu/tegra/libnvcapture.so is empty, not checked.
2023-11-07 23:49:06.271 | DEBUG | bell.avr.mqtt.client:on_connect:292 - Connected with result 0
2023-11-07 23:49:06.273 | SUCCESS | bell.avr.mqtt.client:on_connect:296 - Subscribed to: avr/apriltags/raw

Connecting...
...OK
Error generated. /dvs/git/dirty/git-master_linux/multimedia/nvgstreamer/gst-nvarguscamera/gstnvarguscamerasrc.cpp, execute:740 No cameras available
[WARN:0] global /opt/opencv/modules/videoio/src/cap_gstreamer.cpp (935) open OpenCV | GStreamer warning: Cannot query video position: status=0, value=-1, duration=-1
made it past cap device
terminate called after throwing an instance of 'cv::Exception'
  what(): OpenCV(4.5.0) /opt/opencv/modules/imgproc/src/color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cvtColor'

```

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<div class="post-metadata">

**Author:** ![GioOC8](https://avatars.discourse-cdn.com/v4/letter/g/e68b1a/32.png) [@GioOC8](https://forum.theavr.org/u/GioOC8)\
**Post date:** [November 15, 2023, 4:02am UTC](https://forum.theavr.org/t/april-tag-detection-non-existent-with-errors/760/2 "2023-11-15T04:02:33Z")

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This is likely due to the camera not being connected. Try reconnecting the camera’s ribbon, then turn off and on the drone.

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<div class="post-metadata">

**Author:** ![5A5UK3](https://avatars.discourse-cdn.com/v4/letter/5/48db29/32.png) [@5A5UK3](https://forum.theavr.org/u/5A5UK3)\
**Post date:** [November 15, 2023, 4:38am UTC](https://forum.theavr.org/t/april-tag-detection-non-existent-with-errors/760/3 "2023-11-15T04:38:30Z")

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Hi, thanks for your response. We did try doing that but to no avail

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<div class="post-metadata">

**Author:** ![GioOC8](https://avatars.discourse-cdn.com/v4/letter/g/e68b1a/32.png) [@GioOC8](https://forum.theavr.org/u/GioOC8)\
**Post date:** [November 16, 2023, 3:46am UTC](https://forum.theavr.org/t/april-tag-detection-non-existent-with-errors/760/4 "2023-11-16T03:46:10Z")

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The error says “No cameras available”, so it doesn’t detect the camera. You could try connecting the ribbon to the other port on the VMC and see if that fixes it.