Error loading OpenCV XML file with Python

Question

I'm using OpenCV 2.4.1 and Python 2.7 (Enthought EPD 7.3 running under Visual Studio Python Tools). I'm trying to read an xml file using OpenCV Load() function:

import cv2
import numpy as np

reprojectionError=cv2.Load("calib.xml")

but I'm getting this error:

    reprojectionError=cv2.Load("calib.xml")
AttributeError: 'module' object has no attribute 'Load'
Press any key to continue . . .

Any ideas?

Answer 1

I too had the same error. After searching, I found out some discussion on it in OpenCV bug tracker. From their discussion, what I understood is (of course there are lot of things i couldn't understand like some encoding etc), OpenCV load only valid xml file.

Valid means, it should be some OpenCV structures like IplImage, cvSeq etc. Otherwise it throws some errors.

When I tried to load a haarcascade xml file, It returned NULL.

TypeError: OpenCV returned NULL

When I tried to load some arbitrary xml, (got from somewhere,not related to OpenCV):

error: The node does not represent a user object (unknown type?)

Finally, I loaded an image, saved it in xml file using cv.Save, and tried to load it as follows :

import cv2
import numpy as np

img = cv2.cv.LoadImage('0.jpg',0)
cv2.cv.Save('sof.xml',img)
e=cv2.cv.Load("sof.xml")

print e

And I got the following result, which is correct :

<iplimage(nChannels=1 width=300 height=300 widthStep=300 )>

So what I understood from these examples and discussions on bug tracker is that OpenCV loads only xml files with valid OpenCV structures in it. (And it is a good option. Why should OpenCV try to load all the xml files out there? It have to open only files related to it).

This is what i know about this. Hope it helps !!!