Rootana javascript displays

Introduction

We are exploring ways of being able to view rootana histograms and plots on webpages, rather than in custom GUIs. The current scheme is based on building webpages based on data served up by the ROOT web server : THttpServer.

pecifically, I am running an online rootana analyzer that is serving up the histograms using the THttpServer that is now built into ROOT. Specifically, I am doing something like

/ana.exe -r8088

with the programs in rootana/examples; then I proxy this server through APACHE.

The MIDAS instance I am looking at is here

http://neut18.triumf.ca/

The default browser (the one that ROOT provides) for the rootana histograms is available here

http://neut18.triumf.ca/rootana/

You can use this to explore the histograms I created and plot them. Already that's quite useful. You can see that I have histograms being filled with data from V792 (charge) and V1720 (waveforms); note that this is just simulated data.

You can see that rootana has put the histograms into a ROOT folder called 'Files/output00000387.root'. This is a little hassle, since it means that the ROOT directory where the histograms sit changes when there is a new run; but I wrote javascript to automatically handle that.

The webpage I wrote is available here

http://neut18.triumf.ca/CS/test

The page works by making requests to the THttpServer for the detailed histogram data (AJAX requests), for instance, by grabbing the json description of the histogram here

http://neut18.triumf.ca/rootana/Files/output00000403.root/V792_0_0/root.json

and then filling a plot using the data. I used the dygraph plotting package that Bryerton used for the GRIFFIN display.

I basically tried to recreate the histogram plotting functionality that I have in the rootana display gui. Namely, the ability to choose which channel to look at, the ability to overlay different plots and the ability to display plots side by side. As well as the ability to switch between V792 and V1720 histograms.

In general I think it works fairly well; I could reasonably easily deploy this for different experiments and I think it is fairly responsive and intuitive.

Please feel free to try out the webpage and see how it works. Webpage should also work properly as you start and stop runs. __________________________________________________

Remaining problems

In addition to the general weakness of my html/javascript/css coding, here's some specific problems that still remain with this webpage.

i) The webpage currently only works for looking at the histograms online. You could run rootana on a file and use this webpage to look at the plots; but I don't know how to get the webpage to tell rootana to only process one event at a time, so this isn't so useful. But maybe the idea of using a webpage to look at a particular file doesn't make much sense anyway.

ii) The webpage doesn't know anything about MIDAS events; all it know about are the histograms that it can grab. For instance, this is a problem with the V1720 histograms. If you overlay the first two histogram you should in principle see two peaks that are close together; at least that is what the data looks like in the underlying MIDAS events.

But when viewed with my webpage you often see that the two peaks are far apart. This is because the webpage has grabbed the information for the waveform for one channel, then rootana changed to the next event and then the information for the waveform for the second channel. So you are actually looking at the waveforms for different events, which is confusing.

I can imagine ugly ways of working around this; for instance, I could ensure that the waveform histogram are only filled every second, so that two AJAX would be for the same event. But even that wouldn't always work.

iii) When you pause the webpage, you can't switch between different channels, display types, etc. That is because the webpage only has the information for the histogram that it is currently plotting; it doesn't have information for any other histograms, so can't show them without un-pausing.

In fact, I'm not really sure what the concept of 'pausing' means in this context, given problem ii).

iv) I haven't implemented any histogram reset functionality yet. I think that in principle this THttpServer does support the idea of sending commands back to the program, so I think that this is solvable.

v) Currently I can only plot histograms that are ROOT TH1* format. It should be easy to add the ability to handle TGraph. But TH2D (2D histograms) seems more tricky. It seems that handling 2D plots is not generally something that these javascript plotting packages worry about. I may have found a package that supports this; I will look into this more.

vi) The AJAX data transfers are on the main thread; I'll need to fix that to use the same asynchronous type transfers that Konstantin was writing for MIDAS.

vii) There is some problem with the rootana server when I first restart it. Somehow I have to 'initialize' the rootana server by visiting the default ROOT online browser page. If I haven't done that then my AJAX requests don't work. This needs debugging

I guess that problems i), ii) and iii) are probably problems that we also had with roody (not sure about i). They may be problems that are inherent to trying to decouple the generation of the histograms from their display.