C Zapart1* and Y Shirasaki2 and M Ohishi2 and Y Mizumoto2 and W Kawasaki2 and G Kosugi2 and S Eguchi3
*1Astronomy Data Center, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181- 8588, Japan
2National Astronomical Observatory of Japan, Japan
3Fukuoka University, Japan


The poster showcases a new experimental version 3 of the interactive ALMA WebQL web service in operation at the Japanese Virtual Observatory ( As the size of the publicly released ALMA datasets keeps growing it has become necessary to update the ALMA web service yet again in order to deal with recent increases in data volumes. Whilst version 2 - introduced in 2016 - made it possible to preview smoothly in a web browser 25 GB-large FITS files, version 3 lays foundations towards supporting an interactive preview of terabyte-class FITS files. In addition to handling larger files, ALMAWebQL3 also improves support for real-time spectrum updates through tackling the latency problem in two ways. First, it introduces an adaptive frame rate control: monitoring the network latency and local web browser responsiveness, and reducing the FPS as and when necessary. Secondly, end user's mouse movements are tracked in real time with the Kalman Filter, which is then used to predict the future target mouse position after taking into account network latency and computation time. By predicting mouse movements with the Kalman Filter, the two data streams (FITS spectrum updates over the network and local FITS image zooming in a browser) are close to being kept synchronised. Another innovation is the replacement of the lossless but inefficient PNG image format with a highly efficient but lossy HEVC-based BPG (Better Portable Graphics). This allows us to serve images over bandwidth- constrained connections, better supporting the East-Asian scientific community.

Accompanying ALMAWebQL3 is the FITSWebQL Personal Edition: a version of the ALMAWebQL server software made to run on local end-user computers (laptops, desktops), independent of the Japanese Virtual Observatory. It is freely available for download at . The software can be compiled and run on Linux, macOS and Windows 10 Linux Subsystem (Bash on Windows).


We would like to thank T Kobayashi for various discussions and contributions to the ALMA WebQL service.