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When using the try/catch statement for var data declaration, the program will output 'No License Plate Found', even if there is. If the try/catch statement is removed, the program prints perfectly when there is no License Plate in the frame, but when there is, I get the SyntaxError. Node.js and OpenALPR are installed. Photos are successfully being taken also. OpenALPR expert needed.

const PiCamera = require('pi-camera');


function getRandomInt(max) {
    return Math.floor(Math.random() * Math.floor(max));
}

setInterval(function() {

    var path = './' + getRandomInt(500) + '.jpg';

    const myCamera = new PiCamera({
        mode: 'photo',
        output: path,
        width: 1920,
        height: 1080,
        nopreview: false,
    });


    myCamera.snap()
        .then((result) => {

            var exec = require('child_process').exec;
            var cmd = 'alpr -c eu -n 1 --json ' + path;

            exec(cmd, function(error, stdout, stderr) {

            console.log(stdout);

            try {
               var data = JSON.parse(stdout.trim())
            } catch (e) {
               console.error('Failed to Parse JSON!', e)
            }

                if (data && data.results &&  data.results.length > 0) {
                    console.log(data.results[0].plate);
                } else {
                    console.log("\n\n\nNo license plate found.\n\n");
                }
            });

            console.log(result);

        })
        .catch((error) => {
            console.log(error);
        });

}, 2e3);

The error and where it occurs without try/catch:

  undefined:1
  SyntaxError: Unexpected end of JSON input
    at JSON.parse (<anonymous>)
    at /home/pi/Project/project.js:28:33
    at ChildProcess.exithandler (child_process.js:301:5)
    at ChildProcess.emit (events.js:189:13)
    at maybeClose (internal/child_process.js:970:16)
    at Socket.stream.socket.on (internal/child_process.js:389:11)
    at Socket.emit (events.js:189:13)
    at Pipe._handle.close (net.js:600:12)

Output of console.log(stdout); before var data declaration:

{"version":2,"data_type":"alpr_results","epoch_time":1588355061888,"img_width":1920,"img_height":1080,"processing_time_ms":1447.340698,"regions_of_interest":[],"results":[]}
RO'D
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1 Answers1

1

  1. the data is already a parsed one. the error is throwing because you are trying to parse it again.

  2. .trim() is a string operation. what you are dealing with is a json object. so that is also invalid. JSON.stringify(stdout).trim() is valid though.

pope_maverick
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