Converting Bytes to integers for an AR-Project

Beginners
1

Hey Guys,

I just started working on an Augmented-Reality project. For this project I have a PTZ-Camera and I can send inquiries for Pan, Tilt, Zoom and so on. The problem I have is that the answer comes packaged in 4 bytes (I am just looking at the Tilt Values right now) and I cannot find a way to reconstruct the actual data.

The Data comes in the following format in an TcpIp-Dat:

90 50 0w 0w 0w 0w 0z 0z 0z 0z FF

(from the documentation found here, search for “CAM_PanTiltPosInq“:
https://ptzoptics.com/wp-content/uploads/2020/08/PTZOptics-VISCA-over-IP-Rev-1_2-8-20.pdf )

In this package, the wwww represents the Pan-Value and the zzzz the Tilt-Value. In Wireshark it looks like this:

90 50 0f 0e 04 0e 00 05 01 00 ff

In the TcpIp-Dat with bytes enabled it looks like this:

80 15 14 04 14 00 05 01 00 255

I have found that if I take the zzzz (Tilt-Values) from Wireshark in this example and run them through a Hexadecimal to Decimal converter, it gives me a number I can work with. In this example “0510” gives me “1296”. How I decipher this number to some kind of degrees is another question for another day, but I think it divides 360° of theoretical movement in 256²=65536 Steps and that’s logic I think I can handle.

I know that if I take the Tilt-Values (the bytes) in TouchDesigner “00 05 01 00” and converted them to normal integers I could use math (first number times 16³, second number times 16² and so on) to get that same number. But I have not found a way to convert the bytes to integers.

My question is, how I can get this conversion from bytes to integers done in Python or other Dats. Any help would be much appreciated! I will append my file, so that you could look at what I have done so far!

Thanks

ToelzerKing

PTZ_Converter1 Forum.2.toe (4.4 KB)

2

Look into the ‘struct’ module (it comes with default Python). It allows to to define how an array of raw bytes should be re-interpreted as different types of values (ints, floats etc)

1 Like
3

@malcolm Thank you for your swift answer, I tried:

TiltAngle = struct.unpack(‘=i’, bytes)

and now I get a “struct.error: unpack requires a buffer of 4 bytes”. I have looked thorugh many discussions in different Forums, but haven’t found a clue of what I have to do.

My knowledge in Python is not that great, so any help is, once again, much appreciated.

Thanks
ToelzerKing

4

One tip, in your onReceive callback you should use the ‘bytes’ argument directly, instead of reading a single cell decimal string from the table. The table is mostly a visual aid in this context.

You can pass that bytes argument to your struct pack/unpack calls.

Cheers,
Rob

1 Like
5

@rob Thanks, I implemented that immediately, still getting that “struct.error: unpack requieres a buffer of bytes” though… I’ll continue my search tomorrow.

Thank you for your help! If anyone knows a solution for the problem above, I’m still open for suggestions!

Cheers,
ToelzerKing

6

Hello.
Change your tcp/ip DAT row/col format to ‘One for All Received Data’.

Then change your callback to something like:

import struct

def onReceive(dat, rowIndex, message, bytes, peer):
    	print('R:', len(bytes), type(bytes), bytes)	
    	unpacked_data = struct.unpack('cccHHH', bytes)
    	print('data is', unpacked_data)

The print statements are optional, but tell you how many bytes are in the message, which should guide what you try to unpack from it.

Note: You’ll have to change that format string ‘cccHHH’ to match your actual format.
In this example, I just guessed a 9 byte message consisting of three single characters (c) followed by three two-byte unsigned short integers (H).

If different types of messages are coming in, you’ll have to unpack accordingly.

For a full format list see:

Hope that helps.
Cheers,
Rob