NI Vision OpenCV Utilities package: FindContours wrapper

[MarcoMauri]

Hi,

we are using NI Vision OpenCV Utilities package to write a wrapper for OpenCV.

Do you have some idea on how to pass the contours generated by the FindContours function back to LabView?

Contours data type is the following:

vector<vector<Point> >

Thanks in advance for your help

[Stfn.fois]

Hi MarcoMauri,

can you explain better what do you mean?

You are developing a wrapper in labVIEW, but I don't understand your phrase: "Do you have some idea on how to pass the contours generated by the FindContours function back to LabView?"

If you are developing in LabVIEW, why do you need to pass back a value in LabVIEW? You should already have it...

[MarcoMauri]

Hi!

I was not clear in my first post: we are developing a wrapper for LabView and not with LabView.

It's not easy to call the FindContour function of OpenCv directly in LabView,

so we are developing a wrapper in Visual C compiled as a DLL.

The function FindContour is called in our wrapper and then the result needs to be passed back to LabView.

Since it is not a simple data type but an array of arrays of points, this is quite tricky.

[Stfn.fois]

Hi MarcoMauri,

as you know, with the "CallLibraryFunction" node you can get only simple data types and pointers. I suggest you to share out  the memory location's pointer of your function result. In LabVIEW you can access the data using the MoveBlock function.

Have a look on these links:

https://forums.ni.com/t5/Example-Code/Retrieve-Data-from-a-C-Array-Pointer-in-LabVIEW/ta-p/3996276

https://forums.ni.com/t5/Developer-Center-Resources/Dereferencing-Pointers-from-C-C-DLLs-in-LabVIEW/...

You will find some explenations and examples!

Good luck!

Stefano Fois

[yangqiang]

I have the same question. Do you find a way to solve the problem?

[MarcoMauri]

Here attached I've put some sample code, I hope this helps.

You'll need to include some libreries to compile it, for instance:

#include <C:\Program Files (x86)\National Instruments\NIVision OpenCV Utilities\nivisionextlib\include\NIVisionExtLib.h>
#include "C:\Program Files (x86)\National Instruments\NIVision OpenCV Utilities\nivisionextlib\include\lv_prolog.h"

Hope this helps,

Marco

[Ongelofeloos]

Hi Marco,

I am currently trying to tackle exactly the same problem. There are still some undefined types in your code like 'LVArrayOfArray' and 'LV_Array_XYPoint_Int'. Would you mind sharing your .h file?