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ELCOVISION 10 ELSP Lens Distortion Correction

The rectification modules of ELCOVISION 10 supports lens distortion correction. This leads into an enormous increase of the accuracy of the digital rectification. An example will explain this at best

The following picture shows a facade which was shot with a digital camera. This camera is afflicted with an enormous lens distortion particularly in the wide angle configuration: Just have a look at the significant curved corners in front of the building.

To show the enormous increase of accuracy we do some additional mistakes in this example which would normally lead into very bad results:

Mistake #1:  We use a very bad exposure layout: The camera station was not in front of the facade as it is suggested for good accuracies.
Mistake #2:  We also use a very bad point distribution for defining the rectification plane. Nearly the whole rectification of the façade will be computed from extrapolated data which will also lead in a bad result.

Original picture with the definition points for the rectification plane
Original picture with the definition points for the rectification plane

The conventional digital rectification without distortion correction shows the expected bad outcome: We see very strong distortions, the result is practically useless outside of the definition range of the rectification plane:
Conventional digital rectification without distortion correction
Conventional digital rectification without distortion correction.

In a second attempt we use the exactly same 3d points and the exactly same measurements for the definition of the rectification plane. But now we compensate the lens distortion: We select the correct camera parameters from the combo box and turn the distortion compensation on:

Define ELSP plane by points

The resulting rectification plane is now distortion corrected. In all measuring modes of ELCOVISION 10 we will benefit with an higher accuracy. Even in the line evaluation modes in the various CAD plugins we will gain a higher accuracy.

The digital rectification shows now a correct and accurate result. The largest point error is in the left upper part in the façade. The error is as small as approx. 8 cm which is very good considering the fact that we used a very bad exposure layout and a even worse point distribution for the rectification plane definition.
Digital rectified image using ELCOVISION 10 distortion compensation. Note the god shape of the  building in the background.
Digital rectified image using ELCOVISION 10 distortion compensation. Note the god shape of the building in the background.

Same image as above. The façade was cut out to show more details.
Same image as above. The facade was cut out to show more details.

Please note that the "Reduce Pixel Effect" function in ELCOVISION 10 ELSP not only reduces the pixel noise in the image. It also sharpens the image. We can easily see now the joints of the exposed aggregate concrete plates in the left upper corner of the façade which were nearly invisible in the original image.




Additional Special Functions


There are two special built in functions: "Réseau correct image" and "réseau and distortion compensate image". With only 2 mouse clicks we can calculate an ideal picture from any distorted image source:

Properties dialog of an image
Properties dialog of an image

By clicking any of these two buttons a special rectification plane is added to the image. You can choose between an only réseau correcting rectification plane or an réseau and distortion correcting rectification plane. The following image shows the distortion corrected original image. This is a big benefit if you need photos only for documentation:

Distortion corrected original image. Note that the corners are not curved anymore.
Distortion corrected original image. Note that the corners are not curved anymore.