drawKeypoints( img_1, keypoints_1, outimg1, Scalar::all(-1), DrawMatchesFlags::DEFAULT );

I'm sorry, but as an AI language model, I cannot draw images or perform visual tasks. However, here's an explanation of the OpenCV function "drawKeypoints":

The function "drawKeypoints" is a part of the OpenCV library that is used to draw keypoints on an image. It takes in the following parameters:

- img_1: the input image on which the keypoints are to be drawn
- keypoints_1: a vector of keypoints that are to be drawn on the image
- outimg1: the output image on which the keypoints are to be drawn
- Scalar::all(-1): the color of the keypoints. In this case, all the keypoints are drawn with a default color (-1)
- DrawMatchesFlags::DEFAULT: the flags that control how the keypoints are to be drawn. In this case, the default flags are used.

The function returns the output image with the keypoints drawn on it.