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DMG-2, and DMG-3 indicate pixel-wise F1 scores for no- |
damage, minor-damage, major-damage, and destroyed classes, |
respectively. DMG-mean denotes the harmonic F1 score across |
all damage levels computed based on the following equation. |
F1dmg=4 |
P4 |
c=11 |
F1c+ϵ(4) |
As shown in the columns for extreme classes of not |
damaged and destroyed, i.e., DMG-0 and DMG-3 in Table III, |
we observe superior performance results compared to columns |
DMG-1 and DMG-2 for the minor-damage and the major- |
damage classes due to the strength in the signal for those |
extreme classes. We used one Nvidia Tesla V100 GPU with |
32G Memory to train the model and it took 6 days for the |
training to complete. Adam optimization algorithm was used |
and learning rate and batch size were set at 0.001 and 32. |
Fig. 4. Example model predictions at three locations with varying amounts |
of observed damage. |
Fig. 5. Legend for damage level colors shown in Figure 2 and 4 |
Figure 4 demonstrates the predicted polygons for buildings |
along with their predicted labels. In the second row, the model |
was able to capture two missing buildings in the ground |
truth mask. Green, orange, purple and dark pink colors are |
used to indicate no-damage, minor-damage, major-damage and |
destroyed classes respectively. See figure 5 for legend. |
The baseline model available to our stakeholder shows F1 |
score of 0.64 on the test set for building segmentation, which |
is inferior to our result of 0.74, shown in Table III. For the |
stakeholder’s baseline damage classification performance, we |
do not have access to the results for a comparable data split |
to report here. We also show our model’s performance against |
the baseline model presented in [26] in Table II. Our proposed |
solution demonstrates a significant improvement in damage |
classification task. |
Model BLD DMG |
Baseline 0.79 0.03 |
Ours 0.74 0.58 |
TABLE II |
COMPARISON WITH THE BASELINE MODEL PRESENTED IN [26], BOTH |
RESULTS ARE BASED ON TRAINING MODELS ON THE X BD TIER 1DATASET |
VI. M ODEL ROBUSTNESS TO UNSEEN DISASTERS |
To assess the robustness of the model performance to unseen |
disasters, we conduct four additional experiments outlined in |
Table III. To that end, each time, we leave either the Joplintornado or the Nepal flooding out for testing purposes and |
we train and validate the model based on the random split of |
the remaining data. Additionally, to see the impact of training |
damage classification only based on a specific type of disaster, |
we conduct two additional experiments: (I) when damage |
classification is trained only on wind-caused data, and (II) |
when damage classification is trained only on flood disasters. |
In both cases, the building segmentation module is trained on |
90% of the entire training data; not on a specific disaster type |
as in the damage classifier module. In Table III, the second |
row shows the results for the case when we leave out the |
Joplin tornado for testing purposes and use a random split of |
the remaining data for training and validation for both building |
segmentation and damage classification tasks. For this unseen |
disaster, the harmonic mean of F1 scores on the test set drops |
by 4% compared to the completely random split of the dataset. |
The drop in the performance is more significant, 0.54%, |
when we leave Nepal flooding out as outlined in the fourth |
row of Table III. Regression in performance is also notable |
for the building segmentation task for Nepal flooding. This |
observation can be associated to the geographical distribution |
of the data. Unlike Nepal flooding, the majority of the disasters |
in the dataset, used in the training phase, are concentrated |
around North and Central America, which could explain the |
dramatic decrease in the F1 score when testing the model on a |
completely new geographical region. Test set results outlined |
in rows three and five of Table III demonstrate that training |
the damage classifier on the specific type of disasters boosts |
the performance when testing on a completely unseen disaster |
event. |
VII. I NFERENCE SPEED BENCHMARKING |
Inference speed (specifically, the number of pixels/second |
that a model can process) is an important property of models |
that will be deployed to run on imagery collected from future |
disasters. Slow models will result in larger compute costs and |
potentially delayed results in time-sensitive disaster response |
applications. |
We benchmark the inference speed of the top-ranked |
solutions on the xView2 challenge with our proposed model |
and find that our proposed model is three times faster than |
the fastest winning solution and over 50 times faster than the |
slowest first place solution. Table IV shows the performance |
results of each solution (except for the 4th place solution which |
was not reproducible). To benchmark each solution we use the |
following setup: |
•A NC6 virtual machine instance on Microsoft Azure |
which contains a Tesla K80 GPU. |
•The single input inference script provided in each |
solution’s code release from the official “DIUx-xView” |
GitHub account. If the inference script did not contain a |
flag for enabling GPU acceleration we modified it to use |
the GPU for model inference. |
•Three pre- and post-disaster inputs from the xBD dataset. |
Experiment Train Test BLD-1 DMG-0 DMG-1 DMG-2 DMG-3 DMG-mean |
Random splits 80% at random 10% at random 0.74 0.89 0.43 0.54 0.73 0.60 |
Joplin held out 90% of non-Joplin Joplin only 0.76 0.89 0.50 0.36 0.81 0.56 |
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