Network is no longer connected issue

[suatcoskun]

I frequently faced normal matrix error issues. "Network is no longer connected." I tried to change many different parameters in the config.json file but it did not work for me. Do you have any suggestions on which parameters can be affected by this situtation?

025-02-18 08:05:11,756 - INFO - STEP 1: CONSISTENCY CHECK
2025-02-18 08:05:11,756 - INFO - ---------------------------------------------------------------------------------
2025-02-18 08:05:11,756 - INFO - Parameter value default
2025-02-18 08:05:11,756 - INFO - _________ _____ _______
2025-02-18 08:05:11,756 - INFO - coherence_p1 0.9 0.9
2025-02-18 08:05:11,756 - INFO - grid_size 200 200
2025-02-18 08:05:11,756 - INFO - mask_p1_file None <---
2025-02-18 08:05:11,756 - INFO - num_nearest_neighbours 30 30
2025-02-18 08:05:11,756 - INFO - max_arc_length 999999 <--- None
2025-02-18 08:05:11,756 - INFO - velocity_bound 0.1 0.1
2025-02-18 08:05:11,757 - INFO - dem_error_bound 100.0 100.0
2025-02-18 08:05:11,757 - INFO - num_optimization_samples 100 100
2025-02-18 08:05:11,757 - INFO - arc_unwrapping_coherence 0.6 0.6
2025-02-18 08:05:11,757 - INFO - min_num_arc 3 3

025-02-18 08:08:52,533 - INFO - ########## NOISY POINT REMOVAL BASED ON ARC PARAMETERS ##########
2025-02-18 08:08:52,533 - INFO - Selection of the reference PSC
2025-02-18 08:08:52,597 - INFO - Spatial integration to detect noisy point
2025-02-18 08:08:52,597 - INFO - ITERATION: 0
2025-02-18 08:08:52,799 - ERROR - Singular normal matrix. Network is no longer connected!

[Andreas-Piter]

Dear @suatcoskun,
Creating a robust spatial network of first-order points is an important and sometimes challenging task during SARvey processing.
Could you please provide the following?

• step_0_temporal_phase_coherence.png
• step_1_arc_coherence.png
• your config file

Best, Andreas

[suatcoskun]

Hi @Andreas-Piter

config.zip

Best..,
SUAT

[Andreas-Piter]

Thank you for providing the figures and the config.

I would assume that two things could help you to receive a good first-order network.

1. Mask out the water pixels.
   You can manually create a mask which roughly masks the land area that you are interested in. Please follow this documentation about masking with generate_mask.py.
   Afterwards, you can add this mask file to your config file to both consistency_check:mask_p1_file and filtering:mask_p2_file.

2. Lower the parameter consistency_check:arc_unwrapping_coherence threshold.
   This parameter controls which arcs are removed. Start with a threshold of 0.5 which might already result in a connected network.
   In case this is not yet working, you can lower the parameter consistency_check:num_nearest_neighbours to 10.

Please let me know if the suggestions helped to create a connected network.
Best, Andreas

[suatcoskun]

Thank you @Andreas-Piter when I changed the arc_unwrapping_coherence value to lower number its worked properly. I tried to apply water mask to stack but It's a little difficult to draw precisely. Anyway maybe you can find better way to apply water mask after.

Best...

[Andreas-Piter]

It's good to hear that the processing works well.

I do understand that creating a precise water mask is challenging with the given tool. However, in order to simplify the SARvey processing, a rough water mask is sufficient (see example in the figure). The goal is to exclude the majority of the pixels which are most likely noisy.

[suatcoskun]

Yes this explanation is very clear. I got it.

Thanks.