# How to check a particulate sensor?

Someone asked an interesting question on Facebook. Given the readings from a particulate matter sensor (PM10 and PM2.5), is there a way to “sanity check” the measurements? The question arose because the sensor sometimes provided negative values for the PM2.5 measurements. Was this miscalibration, a bad sensor or an error in the transmission system that left…

# Streamline trajectories

I recently found myself in the situation where I wanted to get the trajectories of streamlines starting from a specific point. Lots of visualization software offer the possibility to plot streamlines. Two of these are Paraview and Tecplot. Paraview is open-source and generally good, although on dense meshes, streamlines tend to stop randomly. Tecplot is…

# Accuracy of Centroid from Image

What is the accuracy of centroid extracted from an image? I recently had a argument with a colleague of mine. Here a  simple test. First generate images with a sphere $n$ pixels in diameter, moving across an image. Then measure the centroid using OpenCV in Python. To keep things simple, I will move the spheres in…

# How to process and store data?

I mainly record my experiments using images. As time progresses I often  want a  new or better measurements, leading me to re-analysing the data. Hence, I often wonder what is the best way to store the data, as analysing thousands of images takes some time. The requirements I found are Speed: It shouldn’t take me…