depth information from Astra camera

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Hello,

I am trying to get the distance to the defined object by using Astra camera with /camera/depth/image_raw topic. By using OpenCV library and RGB image from topic /camera/rgb/image_raw I have defined the object and get the center position of the object. Now I want to get the distance to that center, I read that the depth_image with 32FC1 encoding from depth topic gives you the distance of each pixel in meters. But when I am trying to do that in that way: depth = depth_image[self.position[0], self.position[1]] I got strange value like 1169 or the values which are very close to it regardless of the distance.

Could someone help me regards,