[1pt] PR: Snap crosswalk to NWM streams

[mluck]

Snaps crosswalk from the midpoint of DEM-derived reaches to the nearest point on NWM streams within a threshold of 100 meters. DEM-derived streams that do not locate any NWM streams within 100 meters of their midpoints are removed from the FIM hydrofabric and their catchments are not inundated. Fixes #1194 and resolves #981.

Changes

• src/add_crosswalk.py: Locates nearest NWM stream to midpoint of DEM-derived reaches if within 100 meters. Also fixes a couple of minor bugs.

Testing

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[mluck]

Inundation in 18100201 in the oval area was reported to be false (#981). The current feature branch dev-extend-fix-snap-crosswalk corrects the crosswalking error in the DEM-derived reaches (red dashed lines) and removes the inundation.

[mluck]

The current feature branch dev-snap-crosswalk removes the DEM-derived reaches and catchments if no NWM stream is found within 100 meters of the midpoint of the DEM-derived reach. The effect is that there are areas with no catchments in the HUC (left). However, those areas may be inundated by other branches as displayed in the mosaicked image on the right.

[ZahraGhahremani]

I tested a few HUCs (19020602, 21010004, and 1060001), and the code is working as expected. It removes DEM-derived reaches if they’re not within 100 meters of NWM streams.
The red lines show the DEM-derived streams, and the green lines are the NWM streams. For HUC 1060001, the catchment was previously inundated by some DEM-derived reaches (fim_4_5_2_0), but they’re not affected in the current feature branch since they don’t have NWM streams within 100 meters of their midpoints. This PR doesn’t have any unintended effects.

[mluck]

Results of the evaluation of the crosswalk using the intersection method (using tools/evaluate_crosswalk.py) in the BED HUCs (n=2153):

• The mean evaluation increased from 96.8% to 97.4%
• Evaluation for 1632 HUCs increased, 11 unchanged, and 510 HUCs decreased

[mluck]

More detailed overall stats comparing fim_4_5_2_11 - fim_4_4_15_0:

count    2153
mean        0.006315
std         0.015147
min        -0.078818
25%         0.000048
50%         0.003039
75%         0.007652
max         0.222222

I looked at the HUC that decreased the most. The low performance highlights a known limitation in the evaluation test rather than a reduction in the crosswalk accuracy. For example, in the image below, the midpoint of the DEM-derived reach (dashed red line) is correctly crosswalked to the green NWM feature_id via the snapping method, but the evaluation that compares the number of intersections in the DEM-derived reaches and the NWM streams has more intersections with the solid red NWM stream than the green NWM stream.

[CarsonPruitt-NOAA]

That's great! I'll count this as a pretty big win.