Build instructions for opencv 4.9.0 fails - Error: "in-source builds are not allowed"

[helarsen]

Question

In the README are instructions to build opencv with gstreamer support for version 4.5.4. I have changed the instructions to in stead use 4.9.0 like this:
`sudo apt install -y libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev gstreamer1.0-plugins-ugly gstreamer1.0-rtsp python3-dev python3-numpy

git clone --depth=1 -b 4.9.0 https://github.com/opencv/opencv

cd opencv

mkdir build && cd build

cmake -D CMAKE_INSTALL_PREFIX=/usr -D WITH_GSTREAMER=ON ..

make -j$(nproc)

sudo make install`

In this process, the cmake line gives this error
CMake Error at CMakeLists.txt:10 (message): FATAL: In-source builds are not allowed. You should create a separate directory for build files. -- Configuring incomplete, errors occurred!
What can I do to correct this - apart from doing exactly as the README says? Should it not also work for 4.9.0?
Yes - I know this is not opencv support site! - But the instructions are here.

Rasberry OS Bookworm - Linux pi96 6.6.28+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.6.28-1+rpt1 (2024-04-22) aarch64 GNU/Linux
cmake version 3.25.1
gstreamer 1.22

[helarsen]

Ok figured something out. cmake is apparently itchy about where the build/ and source/ files are relative to each other.
Here is an explicit way of defining where the source/ -S and build/ -B folders are. I did put build/ next to opencv/ folder - to ensure that cmake cannot reasonably complain about "in-source build not allowed!"

sudo apt install -y libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev gstreamer1.0-plugins-ugly gstreamer1.0-rtsp python3-dev python3-numpy
git clone --depth=1 -b 4.9.0 https://github.com/opencv/opencv
mkdir build
cmake -S opencv -B build -D CMAKE_INSTALL_PREFIX=/usr -D WITH_GSTREAMER=ON
cd build
make -j$(nproc)
sudo make install