Categories
cmake code opencv vision work

OMG CMake/OpenCV3 can you be more difficult? Linking order problems with OpenNI2…

So I just spent 1.5 hours figuring this out.
Compiling an example on Ubuntu 16.04 with OpenCV built from scratch with OpenNI2 support.
(OpenNI2 is from Orbbec, but that doesn’t make any difference: https://orbbec3d.com/develop/)
When using this straightforward CMake script for compilation – it doesn’t work:

cmake_minimum_required(VERSION 3.2)
project(MyApp)
find_package(OpenCV 3 REQUIRED)
set(OPENNI2_LIBS "OpenNI2")
link_directories("/home/user/Downloads/2-Linux/OpenNI-Linux-x64-2.3/Redist")
add_executable(myapp main.cpp)
target_link_libraries(myapp ${OpenCV_LIBS} ${OPENNI2_LIBS})

Complains of undefined references:

/usr/bin/c++   -g   CMakeFiles/myapp.dir/main.cpp.o  -o myapp  -L/home/user/Downloads/2-Linux/OpenNI-Linux-x64-2.3/Redist -rdynamic -lOpenNI2 /usr/local/lib/libopencv_shape.so.3.2.0 /usr/local/lib/libopencv_stitching.so.3.2.0 /usr/local/lib/libopencv_superres.so.3.2.0 /usr/local/lib/libopencv_videostab.so.3.2.0 /usr/local/lib/libopencv_objdetect.so.3.2.0 /usr/local/lib/libopencv_calib3d.so.3.2.0 /usr/local/lib/libopencv_features2d.so.3.2.0 /usr/local/lib/libopencv_flann.so.3.2.0 /usr/local/lib/libopencv_highgui.so.3.2.0 /usr/local/lib/libopencv_ml.so.3.2.0 /usr/local/lib/libopencv_photo.so.3.2.0 /usr/local/lib/libopencv_video.so.3.2.0 /usr/local/lib/libopencv_videoio.so.3.2.0 /usr/local/lib/libopencv_imgcodecs.so.3.2.0 /usr/local/lib/libopencv_imgproc.so.3.2.0 /usr/local/lib/libopencv_core.so.3.2.0 -Wl,-rpath,/home/user/Downloads/2-Linux/OpenNI-Linux-x64-2.3/Redist:/usr/local/lib
/usr/local/lib/libopencv_videoio.so.3.2.0: undefined reference to `oniStreamGetProperty'
/usr/local/lib/libopencv_videoio.so.3.2.0: undefined reference to `oniRecorderDestroy'
/usr/local/lib/libopencv_videoio.so.3.2.0: undefined reference to `oniDeviceIsCommandSupported'
/usr/local/lib/libopencv_videoio.so.3.2.0: undefined reference to `oniDeviceSetProperty'

You’ll notice that -lOpenNI2 does indeed appear for correct linking.
The linker doesn’t complain that lib was not found – it just misses the references.
This lead me to understand it’s a linking order problem (after ~45 minutes of banging my head vs. the keyboard and swearing profusely).
Some more swearing and head banging got me to understand that CMake is messing around with the link order.
So even if try:

target_link_libraries(myapp ${OpenCV_LIBS} ${OPENNI2_LIBS} ${OpenCV_LIBS} ${OPENNI2_LIBS})

i.e. making the order effectively meaningless — it still doesn’t work!
More swearing and head banging, another ~40 minutes passed, and I figured out a solution.
The real solution is to slap someone in CMake in the face with a trout, but here’s a solution to my problem:

find_package(OpenCV 3 REQUIRED core highgui videoio) # ORDER MATTERS!!! videoio must be last!
set(OpenCV_LIBS "${OpenCV_LIBS};OpenNI2") #add openni2 at the end (although cmake doesn't keep order anyway)
target_link_libraries(myapp ${OpenCV_LIBS})

Now it compiles.
And look at the make VERBOSE=1:

/usr/bin/c++   -g   CMakeFiles/myapp.dir/main.cpp.o  -o myapp  -L/home/user/Downloads/2-Linux/OpenNI-Linux-x64-2.3/Redist -rdynamic /usr/local/lib/libopencv_highgui.so.3.2.0 /usr/local/lib/libopencv_videoio.so.3.2.0 -lOpenNI2 /usr/local/lib/libopencv_core.so.3.2.0 -Wl,-rpath,/home/user/Downloads/2-Linux/OpenNI-Linux-x64-2.3/Redist:/usr/local/lib -Wl,-rpath-link,/usr/local/lib

Can you see how highgui and videoio are before OpenNI2, and core is after?
Why? Whhhhhhy?
The key is to get OpenNI to be linked in order after videoio.
OMG CMake, OMG OpenCV, OMG you gaiz, W-T-F?
Update:
This method breaks down as soon as more OpenCV components are added. The order goes haywire again, and OpenNI2 comes before videoio, which breaks the link.
As of now the way I can compile it is like so:

set(LINK_LIBS /usr/local/lib/libopencv_core.so.3.2
              /usr/local/lib/libopencv_highgui.so.3.2
              /usr/local/lib/libopencv_videoio.so.3.2
              /usr/local/lib/libopencv_imgproc.so.3.2
              /usr/local/lib/libopencv_calib3d.so.3.2
              OpenNI2)
Categories
code opencv vision

New edition to the Mastering OpenCV book – now with OpenCV3!

Mastering OpenCV 3
I’m happy to announce that the new edition of Mastering OpenCV is out!
You can get it on Amazon: Mastering OpenCV 3
It brings up most of the older OpenCV2 book projects to OpenCV3, including my Toy-SfM (or “Exploring SfM”) project.
A lot has happened in the OpenCV3 APIs with respect to Structure from Motion.
It got much easier!
The book chapter on SfM is a gentle introduction to the subject, that focuses on coding and the core concepts, while abstracting on the math.
Thanks for listening!
Roy

Categories
Android Java video

Android Camera2 Touch-to-Focus

Man Camera2 APIs are hard to master…
I’ve scanned SO for a way to get touch-to-focus to work on Android and could not find a solution that works.
These were very partial, or provided only scaffold code which I couldn’t use:

Finally I was able to do it by myself this way:

Enjoy
Roy

Categories
code programming python Solutions Web

A script to scrape PDFs from a page using Python+Mechanize

A friend asked me for a way to download all the PDFs from a page, and I made this simple script with Python and Mechanize. It’s very straightforward…
It does hack the user agent, which is not nice. So use at your discretion.

Categories
3d code opencv programming vision

Structure-from-Motion Toy Lib Upgrades to OpenCV 3

sfm toy lib
Hello again!
After a long hiatus I’m back with an update. Recently I’ve been upgrading the Structure-from-Motion Toy Library (https://github.com/royshil/SfM-Toy-Library/) to OpenCV 3.x from OpenCV 2.4.x.

Categories
3d code graphics gui opengl qt

WTH OpenGL 4? Rendering elements arrays with VAOs and VBOs in a QGLWidget

I spent an entire day getting OpenGL 4 to display data from a VAO with VBOs so I thought I’d share the results with you guys, save you some pain.
I’m using the excellent GL wrappers from Qt, and in particular QGLShaderProgram.
This is pretty straightforward, but the thing to remember is that OpenGL is looking for the vertices/other elements (color? tex coords?) to come from some bound GL buffer or from the host. So if your app is not working and nothing appears on screen, just make sure GL has a bound buffer and the shader locations match up and consistent (see the const int I have on the class here).

Categories
code opencv python video

[Python] OpenCV capturing from a v4l2 device

I tried to set the capture format on a webcam from OpenCV’s cv2.VideoCapture and ran into a problem: it’s using the wrong IOCTL command.
So I used python-v4l2capture to get images from the device, which allows more control.
Here is the gist:

Enjoy!
Roy

Categories
code opencv python

OpenCV Python YAML persistance

I wasn’t able to find online a complete example on how to persist OpenCV matrices in Python (so really NumPy arrays) to YAML like what cv::FileStorage will give you.
So here’s a short snippet:

import numpy as np
import yaml
# A yaml constructor is for loading from a yaml node.
# This is taken from: http://stackoverflow.com/a/15942429
def opencv_matrix_constructor(loader, node):
    mapping = loader.construct_mapping(node, deep=True)
    mat = np.array(mapping["data"])
    mat.resize(mapping["rows"], mapping["cols"])
    return mat
yaml.add_constructor(u"tag:yaml.org,2002:opencv-matrix", opencv_matrix_constructor)
# A yaml representer is for dumping structs into a yaml node.
# So for an opencv_matrix type (to be compatible with c++'s FileStorage) we save the rows, cols, type and flattened-data
def opencv_matrix_representer(dumper, mat):
    mapping = {'rows': mat.shape[0], 'cols': mat.shape[1], 'dt': 'd', 'data': mat.reshape(-1).tolist()}
    return dumper.represent_mapping(u"tag:yaml.org,2002:opencv-matrix", mapping)
yaml.add_representer(np.ndarray, opencv_matrix_representer)
#example
with open('output.yaml', 'w') as f:
    f.write("%YAML:1.0")
    yaml.dump({"a matrix": np.zeros((10,10)), "another_one": np.zeros((2,4))}, f)
#   a matrix: !!opencv-matrix
#     cols: 10
#     data: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
#       0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
#       0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
#       0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
#       0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
#       0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
#       0.0, 0.0, 0.0, 0.0, 0.0]
#     dt: d
#     rows: 10
#   another_one: !!opencv-matrix
#     cols: 4
#     data: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
#     dt: d
#     rows: 2
with open('output.yaml', 'r') as f:
    print yaml.load(f)
#  {'a matrix': array([[ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
#         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
#         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
#         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
#         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
#         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
#         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
#         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
#         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
#         [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.]]), 'another_one': array([[ 0.,  0.,  0.,  0.],
#         [ 0.,  0.,  0.,  0.]])}

There you go

Categories
apache code Java programming Web

Simple Loading Spinner Tapestry 5 Mixin w/ spin.js

Sharing a small snippet on creating a loading spinner in a Tapestry 5.3+ Mixin, using spin.js.
It creates a convenient way to add spinners to your long-loading-times ajax zone updates, with all the code hidden away from the template .tml and page class object.
Sorry I can’t show a working example, that would entail running a Tapestry application server.
But it’s very straightforward, just grab the spin.min.js and the rest falls into place (it also depends on jQuery).

Categories
code Web

Adding radial labels to Dimple.JS pie chart

Too bad Dimple.JS doesn’t have this feature built-in. They only have a boring old legend, where pie charts scream for labels that circle the actual pie (or donut).
Anyway, here’s how to get it done using some d3.js love.