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Surf is looking for eye-catching points. This occurs inter alia by the contrast between the umligenden pixels. I think your buildings have very few of these points.

Here are some Tips:

• Use Grayscale Images (ore cast them to Grayscale)
• Sharp them (Sharp Image = Original Image - Gausian(Original Image))

Maybe you can try a Sobel and add it to the sharpened Images. I think that would give you more matching Keypoints at the roof area and on the buildings.

You should also use a dynamic threshold for matching!. Like:

if((matches2[i][0].distance < 0.56*(matches2[i][1].distance)) && ((int) matches2[i].size()<=2 && (int) matches2[i].size()>0))

You could also try a KNN-Matcher instead of a BF-Matcher.