State of the art; Automatisk sprickmätning av vägbanor

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The need for objective collection of crack information has increased in Sweden. The type of wear of the road surfaces has changed. New, more stronger and long lasting pavements have been developed. The use of lightweight studs has also changed the degree of wear. The use of thin pavements increases and the designed life expectation has grown. The amount of heavy traffic increases and maximum allowed axle load, as well as maximum allowed tire pressure increases. All this leads to a change from the traditional measures like rut depth to more adequate measures like crack information. In USA, Japan and south of Europe there is a tradition in inventory of cracks. That is the reason why so many of the existing crack measuring systems has their origin here. The first automatic systems were actually half automatic, they collected pictures of the surface and in a post process the pictures was subjectively judged to describe cracks. The judgment to classify consists of two phases, severity level and degree of seriousness. This manually inspection is a time consuming process and has a low level of repeatability. The first semiautomatic systems used film that had to be developed. This is still used but the technique to acquire films has improved and continues to improve. There are mainly three types of techniques that are used to day, namely:

1. Traditional video (analogue and digital)

2. Line scan video (analogue and digital)

3. Distance measuring laser cameras (point or line scan)

As examples of the three different techniques the following systems can be mentioned: 1: PAVUE/Laser RST and WiseCrax (ARAN), 2: HARRIS, 3: G.I.E. Laser Vision and Laser RST.

To get a complete automatic crack-measuring system there is also a need for an automatic classification and judgment. This is still the most difficult part to achieve. A lot of processor power and a well functioning classification model are needed to do this. To reduce the amount of data it would be an advantage to do this in real time.  

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