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the R@10 score by 12.4%. Another important observa- |
tion is that the effect of removing meta-information dur- |
ing inference is less severe when using dropout. Hence, |
our model achieves good cross-view retrieval scores even if |
meta-information is not available during inference. |
Figure 3 shows the top 9 closest images retrieved from a |
given overhead image. We see that our model is able to re- |
trieve ground-level images by relating concepts rather than |
direct visual matching. For example, in (a), our model re- |
trieves images of people playing golf for an overhead image |
of a golf course. Similarly, in (d), our query image seems |
to be located over a farm. Here, Sat2Cap has learned to |
associate the concept of farmland with cattle and livestock. |
It retrieves images of horses and goats which are concepts |
that likely reside in the location but are not visible in the |
overhead image. This suggests that our model can map fine- |
grained concepts of the ground-level scene to a given geolo- |
cation. Sat2Cap is also capable of dynamic image retrieval. |
Figure 4 shows the top 9 images retrieved at two different |
6 |
Figure 5: Country-level maps of textual descriptions : (Col 1-2) shows the country-level maps created using Sat2Cap for |
two prompts: “Kids playing in the sand” and “A busy street in downtown”. (Col 3) shows a landcover map of the respective |
countries for comparison. |
time settings (11:00 p.m. vs 08:00 a.m.). |
4.2. Application 2: Fine-grained and Dynamic Cap- |
tion Generation |
Our embedding space captures detailed and fine-grained |
textual concepts for geographic locations. While the CLIP |
space can only provide coarse-level generic descriptions |
from an overhead image, our model learns more fine- |
grained visual concepts that someone on the ground might |
observe. To generate captions from our embeddings, we |
use the CLIPCAP [1] model, which maps CLIP space to |
text space. |
Figure 1 shows that using CLIP embeddings of the over- |
head images, the model can only describe generic concepts |
of a location like a beach, island, property, etc. Our Sat2Cap |
embeddings on the other hand produce much more fine- |
grained, as well as, aesthetically pleasing captions. For |
example: in figure (a) CLIP generates the caption “aerial |
view of a beach” missing out on other important details of |
the area. Our model on the other hand generates the cap- |
tion “sea facing apartment with swimming pool, terrace in |
a quiet residential area”, capturing many intricate concepts |
that reside within that location. |
Sat2Cap also models temporal variations allowing us to |
generate different captions for different times. Figure 1 |
shows the captions generated for two different months, Mayvs. January. We see that the model reasonably accounts |
for the seasonal variations for different months of the year. |
However, in figure (d), we see that the model does not add |
any cold/winter-specific information for the January input. |
This is expected behavior since the image is from Australia, |
where the month of January falls right in the middle of sum- |
mer. |
4.3. Application 3: Zero-Shot Map of Fine-grained |
Concepts |
We use the rich Sat2Cap embedding space to create |
country-level maps of fine-grained textual prompts in a |
zero-shot manner. Firstly, we choose two countries to cre- |
ate maps: England and Netherlands. Then, we download |
satellite imagery that covers these regions. Specifically, we |
download 800x800 patches of Bing Map Images at 0.6m/px |
resolution. We precompute the Sat2Cap embeddings for all |
the images and save them on a disc. Now for any given |
text query, we compute the similarity of the CLIP text em- |
bedding with all overhead images of the region. Then we |
normalize these similarities between 0and1and use the |
normalized similarities to create textual maps. The process |
of computing similarities for an entire country took only |
about 4-5 seconds. Hence, our framework is quite efficient |
for mapping large regions and thus could be easily extended |
to map the entire world. |
7 |
Figure 6: Localizing textual queries at finer resolution : For each prompt, the image on left shows the big region which is |
used for inference. The image on the right shows an image of the ground-level scene at the point with the highest activation, |
which was taken by entering the location in Google Maps |
Figure 5 shows the maps for two prompts: “Kids playing |
in the sand” and “A busy street in downtown”. We added the |
phrase “a photo of” at the beginning of each prompt. For |
the first prompt, we see that our model activates locations |
around the ocean and beaches. Activations in both coun- |
tries are high in areas where you might observe a kid play- |
ing in the sand. The second prompt activates locations with |
major cities in both countries. For England, we see high |
activations around London, Oxford, Birmingham, Manch- |
ester, Liverpool, etc. For the Netherlands, we see high acti- |
vations in Amsterdam, Rotterdam, The Hague, Maastricht, |
Groningen, etc as well as other smaller cities. We compare |
this map with ESRI’s Sentinel-2 landcover map. From the |
landcover maps, we see that our model correctly activates |
the fine-grained prompt “A busy street in downtown” in the |
urban areas. Thus, we introduce to a novel way to create |
large-scale maps in a zero-shot setting. |
4.4. Application 4: Geolocalizing Textual Queries |
Our model can be used to localize textual queries at a |
finer resolution. For this experiment, we draw a 24km2 |
bounding box over a region. We compute the Sat2Cap sim- |
ilarity for all the overhead images in that box with a given |
text query. We, then, normalize the similarities between 0 |
and1and clip the values below 0.5. Figure 6 shows the |
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