PointCloudLibrary/pcl

IntegralImageNormaEstimation could/should return signed curvature

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#2,289 opened on Apr 26, 2018

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good first issuekind: proposalkind: todomodule: features

Description

Your Environment

  • Operating System and version: Ubuntu 18.04
  • Compiler: gcc 7.3
  • PCL Version: 1.8.1 & trunk

Context

IntegralImageNormalEstimation computes curvature of the surface when used with normal_estimation_method=COVARIANCE_MATRIX. It does not provide the information about the direction of curvature (towards the normal or away from it) as the sign is discarded - https://github.com/PointCloudLibrary/pcl/blob/9084aec8cdd4bc040f24193b5a767d8dfe153299/features/include/pcl/features/impl/integral_image_normal.hpp#L247 (note the fabsf). In my application (height map), this information is important for further processing (distinguising valleys from hills).

Expected Behavior

I am proposing to make the curvature optionally signed, by adding a flag (false by default, not to break existing code) which would keep curvature sign, plus take in account whether the normal was flipped (in that case, curvature would have to be negated to be consistent).

Current Behavior

Sign of curvature is currently discarded by the fabsf as explained above.

Possible Solution

I suggest I will do a PR to implement this, but I would like to have opinion/guidance from upstream as to whether the chane is mergeable or I better subclass IntegralImageNormalEstimation and keep using that one in my project. Thanks!

Contributor guide

Tech stack
cpp
Domain
data
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++PCLPoint cloud processing
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
The issue is to add an optional flag to return signed curvature in IntegralImageNormalEstimation. The relevant file is `features/include/pcl/features/impl/integral image normal.hpp` at line 247, where fabsf discards the sign. A new boolean parameter (default false) should control whether sign is returned, and curvature sign must be negated if the normal was flipped.