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How to use Virtual feeds:

1 - To create a Virtual feed click "New Virtual Feed" on the feeds menu bottom.

2 - A popup will appear, you should specify the type of data this virtual feed will work with:

• Daily - For 24 hours data only, if using source feeds of daily type.
• Realtime - For all data that has update time different than a day. You can also use this for daily data but it will be slower.

3 - Then you must configure the processlist for the virtual feed, click the wrench icon for it on the feed menu.

4 - All virtual feeds need to source data from existing feeds. That is done with a special processor: 'Source Feed' that need to be added as the first processor.

Source Feed:

Virtual feeds should use this processor as the first one in the process list. It sources data from the selected feed.
The sourced value is passed back for further processing by the next processor in the processing list.
You can then add other processors to apply logic on the passed value for post-processing calculations in realtime.

Note: This virtual feed process list is executed on visualizations request that use this virtual feed.

A simple example to get a Virtual feed that show only the power consumed on high cost schedule:

Created two virtual feeds for each of the rate schedules using the same source feed data (measured power):

And the resulting Multigraph shows the measured power for each schedule in a different color :

Just a note:
An experimental setting is available for configuration if using mysql or memory engine only :

$data_sampling = false;

This will scan all data points with source feed processor so average values will be correctly calculated, but it is 20x slower than sampling method.

The way Vitrual engine get_data method works :

When a graph uses a virtual feed that method is called with graph start, end time and interval to display.

1 - Calculates date slots for given start, end and interval. Representing about a pixel on the x axis of the graph for each time slot.

2 - If feed is realtime slots are calculated based on interval, if daily, slots date is at its datetime midnight of user timezone.

3 - Executes virtual feed processlist for each slot individually.

   ->  First processor of virtual feed processlist should be the source_feed_data_time() this will get data for a time slot.

4 - Agreggates all time slots and processed data.

5 - Returns data to the graph.

Can the virtual feed be output via MQTT?

Ay sheppy. you missed the concept of  virtual feed with that question.
Virtual feeds are calculated on the fly when you query data (from a graph).
How would you do that publishing to mqtt?

You can however publish the feed that sources a virtual feed to mqtt, as usual from the input processlist.

Apologies, I did misinterpret.

What I would like is the ability to output a feed value via MQTT.

With EMONCMS Low Write 8.5 I have to use the raw MQTT input that goes into EMONHUB and add it to other feeds using OpenHAB which duplicates what EMONCMS is doing. I use it to  turn appliances On and Off to avoid exporting / importing Grid Power.

Does EMONCMS 9 offer this?

sheppy

What hardware & operating system are you using?

Paul

Sorry.. in where position is configured the virtual feed ?

I tryed see the database via phpmyadmin but i dont find any reference to the virtualfeed..

I do this questions because after configuring 65 feed i  have try configure 1 virtualfeed but after this operation  i get error and lost all my work,.

Now i can see in input page ( in field process list ) 'wait...'  and in feed list page 'loading..'

In database i can see all my feed in 'feeds' table.. also my input in 'input' table..

I would try manually delete the virtualfeed reference that has determined the problem, but do not understand where are placed this information..

My system il PI with jessie and last emoncms ( 9.1 last realase )

Ceers,

Fabrizio.

( sorry for my english.. )

Its in feeds table with engine = 7.

:) Thanks chaveiro..

I have deleted the record in feed with engine = 7 and now emoncms is OK.

.. but i see this problem again ..

I configured a new virtual feed as daily type.. but as source feed i cannot see any feed configured in daily type ( is available in list only the realtime feed ).

The source feed list are the same for both   ( daily or realtime )

my needed is measure the daily COP of Heath Pomp as energyusagedaily / energy productiondaily

is possible use virtualfeed for do this relations ?

( In old Emoncms, before virtualfeed , i route back the normal feed  as input for do this feature.. )

( i use the last 9.1 version in low-write mode.. )

All my daily feed are configured as mysql timeseries..

Ciao,

Fabrizio.

There is somethings wrong related to virtualfeed..

I get this error during visualisation of one virtualfeed :

Fatal error: Uncaught exception 'Exception' with message 'ABORTED: Call to undefined module method. Missing function on module? method=getstartday' in /var/www/emoncms/Modules/process/process_model.php:50 Stack trace: #0 /var/www/emoncms/Modules/feed/engine/VirtualFeed.php(78): Process->__call('getstartday', Array) #1 /var/www/emoncms/Modules/feed/engine/VirtualFeed.php(78): Process->getstartday(1446673411) #2 /var/www/emoncms/Modules/feed/feed_model.php(386): VirtualFeed->lastvalue(97) #3 /var/www/emoncms/Modules/feed/feed_model.php(343): Feed->get_timevalue(97) #4 /var/www/emoncms/Modules/vis/vis_controller.php(77): Feed->get(97) #5 /var/www/emoncms/core.php(64): vis_controller() #6 /var/www/emoncms/index.php(146): controller('vis') #7 {main} thrown in /var/www/emoncms/Modules/process/process_model.php on line 50

After that emoncms stop to work and need open database via phpmyadmin and delete the engine 7 record in feeds..

This is the record :

New Virtual Feed,  1,  Virtual,  NULL,  NULL,  2,  0,  NULL,  7 53:19,30:45

Hi, update to latest version and see if its ok now.

The error you describe may be related to creating a virtual feed that use other feeds than deleting some of that other feeds.

There is a new version?

I just use this .

9.1 | 2015.11.02.

Thanks,

fabrizio.

Hi fcattaneo 

Did you every fix this as i think im having the same problem

ones i'v add the Virtual Feed and add the feeds emoncms freed stop loading see images

i get the same error in the emoncms logs 

Fatal error: Uncaught exception 'Exception' with message 'ABORTED: Call to undefined module method. Missing function on module? method=getstartday' in /var/www/emoncms/Modules/process/process_model.php:50

and the only way i can get evering back up and runing is to delete the Virtual Feed with phpmyadmin

Thanks Steve

I gave up trying virtual feed with daily data .. I think that is sometings not right.

Also  virtualfeed with realtime data have some problems .. work fine but give strange results.

for example I have a virtualfeed that calculates the difference between two feed (two temperatures) and the result is always wrong to offset .. at this time T1 = 34, T2 = 34,  Virtualfeed = 0.2 instead of 0.

Ciao..

Fabrizio.

Thanks Fabrizio

chaveiro is this something that will be fix in the next update

Thanks Steve

Try 9.2 there was some minor issues that caused what you described.

Not sure about daily data though...

Theres 9.2 have you got a link for download 

It OK it in the git update 

Hi Chaveiro

Great job the Virtual Feed are now working for me :D

Thanks Steve

Great job !!

Now it seems that works .

thanks :) !!!

Hi

I'm seeing a problem with virtual feeds. I have a virtual feed which used another feed in the process list (process /feed).

/feed (divide) where the feed is virtual has to be the last processing option as it seems that anything after it fails.

I tried to multiply by (say) 2 with (calibration) x 2 after the /(virtual)feed and the multiplier was ignored.

I've got it working by using the /(virtual)feed as the last processing action but thought someone should know....

V9.2 | 2015.11.27

Thanks

Mike

I have the same problem in the version 9.31 and I have reported it in GitHub as issue:

https://github.com/emoncms/emoncms/issues/487

I am trying to resolve it, because it forces me to use a normal feed to do the same.

Edit - duplicate posts deleted - Moderator, BT
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