Opencv

cross compile

To compile an OpenCV program on an x86 server for an ARM platform, you’ll need to use cross-compilation. Here’s a general guide on how to do it:

1. Set Up Your Cross-Compilation Environment

Install Required Tools

You will need a cross-compiler for ARM. For example, you can use the gcc-arm-linux-gnueabi or gcc-arm-linux-gnueabihf toolchain.

On a Debian/Ubuntu system, you can install it using:

sudo apt-get update
sudo apt-get install gcc-arm-linux-gnueabi g++-arm-linux-gnueabi

For ARM64 (AArch64):

sudo apt-get install gcc-aarch64-linux-gnu g++-aarch64-linux-gnu

Install CMake

Make sure you have CMake installed:

sudo apt-get install cmake

2. Download and Prepare OpenCV

Get OpenCV Source Code

Download the OpenCV source code from the official repository or website.

git clone https://github.com/opencv/opencv.git
cd opencv
git checkout <desired-version>  # e.g., git checkout 4.5.1

Create a Build Directory

Create a directory for the build process:

mkdir build
cd build

3. Configure the Build with CMake

Use CMake to configure the build system for cross-compilation.

cmake -DCMAKE_TOOLCHAIN_FILE=../platforms/linux/arm-gnueabi.toolchain.cmake -DOPENCV_EXTRA_MODULES_PATH=../../opencv_contrib/modules ..

If you don’t have a predefined toolchain file, you can create one. Here’s an example for ARM:

Create a Toolchain File

Create a file named arm-gnueabi.toolchain.cmake with the following content:

# the name of the target operating system
set(CMAKE_SYSTEM_NAME Linux)

# which compilers to use for C and C++
set(CMAKE_C_COMPILER   arm-linux-gnueabi-gcc)
set(CMAKE_CXX_COMPILER arm-linux-gnueabi-g++)
set(CMAKE_INSTALL_PREFIX /your/target/install/prefix)

# where is the target environment located
set(CMAKE_FIND_ROOT_PATH  /path/to/your/target/rootfs)

# search for programs in the build host directories
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)

# for libraries and headers in the target directories
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

# Adjust the following paths to your toolchain
set(CMAKE_SYSROOT /path/to/your/target/rootfs)

Modify the paths to match your setup.

4. Build OpenCV

Run the build process using make.

make -j$(nproc)

5. Install OpenCV

After the build completes, install OpenCV to the specified location.

make install

6. Cross-Compile Your OpenCV Program

Now you can cross-compile your OpenCV program.

Create a Simple Program

Create a simple program, e.g., test.cpp:

#include <opencv2/opencv.hpp>

int main() {
    cv::Mat img = cv::imread("test.jpg", cv::IMREAD_COLOR);
    if (img.empty()) {
        return -1;
    }
    cv::imshow("Display Image", img);
    cv::waitKey(0);
    return 0;
}

Cross-Compile Your Program

Create a CMakeLists.txt file for your program:

cmake_minimum_required(VERSION 3.0)
project(TestOpenCV)

find_package(OpenCV REQUIRED)
include_directories(${OpenCV_INCLUDE_DIRS})

add_executable(test test.cpp)
target_link_libraries(test ${OpenCV_LIBS})

Create a build directory for your program:

mkdir build
cd build

Run CMake with the toolchain file:

cmake -DCMAKE_TOOLCHAIN_FILE=path/to/your/arm-gnueabi.toolchain.cmake ..
make

This should produce an executable that you can run on your ARM platform.

7. Transfer and Run on ARM Platform

Transfer the compiled executable and any necessary libraries to your ARM platform using scp or any other file transfer method.

scp test user@arm_device:/path/to/destination
scp -r /your/target/install/prefix/lib user@arm_device:/path/to/destination/lib

On your ARM device, you may need to set the library path:

export LD_LIBRARY_PATH=/path/to/destination/lib:$LD_LIBRARY_PATH
./test

This should run your OpenCV program on the ARM platform.