Working with live streaming data is about as good as it gets when it comes to programming – this is especially true if you’re working on a project that looks to create a recognizable relationship between live data and media. What, then, is a person to do when placed in a situation without access to a live source of data? Whatever the project, the best way to tackle this problem is to find a source of prerecorded information. If you’re working on something like motion tracking, using a pre-recorded video is an excellent solution to this problem. What about sensors that aren’t image based? What if I’m dealing with a series of floats? What happens if those floats just come to me in a table? How can I take a series of recorded data points that live in an text file and make them move? That’s exactly one of the problems that came up for me recently, and I’ve got a handy trick that will make it easy to work with a data set in a table as though it were streaming into your TouchDesigner network live.
To get started, we need a file with some data in it. I made a quick spreadsheet with two columns. One starts at 0.01 and goes up to 1, awhile the other column starts at .99 and counts down to 0. If you’re following along, you can download that text file here (tabledata). In broad terms, what were going to make is a simple network of operators that moves through a table, pulling one row of data at a time, and then converting that table information into CHOP data. We can see where we’re headed if we look at our whole completed network:
So what’s happening here? In the DAT called “data” we have a table of recorded values. Next I use a select to remove the header row from the data, and another select to move through the rows of data. Using another table, a transpose, and a merge gives us a table that’s easy to convert into a CHOP. Now that we have a general sense of what’s happening in this network, let’s dig-in and get to work.
We’ll start by adding a Table DAT to an empty network. Rather than entering data by hand, we can instead just point TouchDesigner to a file that we want it to use. In the Table DAT’s parameters dialogue we’ll click on the plus button to the right of the “file” field and then locate the file that we’re looking to use.
In order to see our table data we need to click on the button “Reload File” so that our table will be populated with the information from the file that we’re using. Next we’re going to use a few Select DATs to manipulate the contents of our table. We’re going to use the first select to remove the header row of our table. To set this up, we’ll set our select to extract rows by index, starting at 1.
You’ll also notice that specifying that we’re extracting rows by index turns on a End Row Index value that’s driven by an expression (me.inputs[0].numRows – 1). We’re going to use the logic from this expression a little later on, so tuck that into the back of your mind for just a moment.
Next we’ll use another Select Table to move through the rows of our table. In adding another Select, let’s again set it up to extract Rows by Index. This time, however, we’re going to change the value of the start row and end row index to be the same. Doing things, you should notice that we get only one row of our table. Try changing the values of these parameters – as long as both fields contain the same number you’ll see only one row of information. We’ll animate that in just a moment taking advantage of this.
The next operator that we’ll add to this network is a Transpose DAT. A transpose will change rows into columns, giving us a result that’s two rows, rather than two columns of data.
While just these changing values are ultimately what I’m after, I would also like my values to have names. To do this I’m going to add another table DAT, creating two rows: xPos and yPos. I’m going to use a Merge DAT to combine these two tables – to make this work properly we’ll need to set the Merge to append columns. When we’re doing we should have something that looks like this:
Alright, not that we have our DAT string’s set up, let’s animate this table, and look at how to get some CHOP data out of these DATs. First let’s start by adding a Constant CHOP to our network. Let’s give our first channel a useful name, and then call our absolute frame count (me.time.absFrame).
Why use absolute frame? I’d like a steadily increasing integer that can be used to drive our progression through the rows of our table. Our absolute frame is an excellent candidate for this need – except that I don’t want to exceed the maximum number of rows in my table. To do this let’s add a Limit CHOP. First up I’ll need to set this Operator to Loop, I’ll also want to set this operator to start at 0 (Minimum).
For the maximum value, I want to use the total number of rows in our second table (the table that contained only data, without a header). I could hard-code this by entering 200 into the Maximum parameter of our Limit, but then I have to change this number whenever my table changes. A better solution would be to use an expression to pull this number from the table in question – which is exactly what that expression we saw earlier does. The expression we want to use then for our Maximum parameter is: op(‘select1’).numRows.
Now it’s the moment we’ve been waiting for. Lets make that table move! To do this we’ll use the row counter in to drive our location in our table – we’ll write some relative references in our select2 DAT to make this happen. In the Start Row and End Row Index values let’s use the reference op(‘limit1’)[‘row’] to drive the change in our table.
The last step here is to add a DAT to CHOP to our network. We’ll add this at the end of our network, and drag the target DAT onto the CHOP.
There we have it. We’ve just taken a static table full of data, and turned it into a channel data that changes over time. For extra credit, add a Trail CHOP to the DAT to see what your data looks like.
Matthew Ragan 