1. A method, comprising: accessing a depth map that includes a plurality of depth pixels, the depth map is associated with an image coordinate system having a plane; estimating a local orientation for each depth pixel in a subset of the depth pixels, the local orientation includes an in-plane orientation relative to the plane of the image coordinate system, determining the local orientation for the in-plane orientation comprises: determining a closest point between a test depth pixel and a reference line of an object in the depth map, and determining a rotation invariant angle for the test depth pixel based on an angle between a reference axis and a line between the test depth pixel and the closest point; defining a local coordinate system for each of the depth pixels in the subset, each local coordinate system is based on the local orientation of the corresponding depth pixel; defining a feature region relative to the local coordinate system for each of the depth pixels in the subset; transforming the feature region for each of the depth pixels in the subset from the local coordinate system to the image coordinate system; and using the transformed feature regions to process the depth map.