{"id":6096,"date":"2018-08-24T05:22:57","date_gmt":"2018-08-24T03:22:57","guid":{"rendered":"http:\/\/www.sigterritoires.fr\/?p=6096"},"modified":"2018-10-17T12:05:54","modified_gmt":"2018-10-17T10:05:54","slug":"how-to-create-tanakas-illuminated-contours-with-qgis","status":"publish","type":"post","link":"https:\/\/www.sigterritoires.fr\/index.php\/en\/how-to-create-tanakas-illuminated-contours-with-qgis\/","title":{"rendered":"How to create Tanaka’s illuminated contours with QGis"},"content":{"rendered":"\r\n

The Tanaka\u2019s contours are a method of displaying terrain developed by Professor Tanaka Kitiro in 1950. Tanaka called his technique the \u00ab\u00a0Relief Contours Method\u201d. However, it is usually called the \u201cIlluminated Contour Method\u201d or the \u201cTanaka Method\u201d.<\/p>\r\n\r\n\r\n\r\n

This method applies a light source north-west at a contour map. The result is a 3D style representation of the terrain. The method involves changing the width and colour of the contour lines based on their position relative to the light source: The contour lines that face the light source are drawn white while those found in the shadow are traced in black; the lines perpendicular to the light source are drawn finer than the parallels. In summary, this method gives a realistic shadowy effect to the terrain maps and allows the viewer to better understand the features of the landscape.<\/p>\r\n\r\n\r\n\r\n

We will start with a layer of polylines containing isobath and \/ or contour lines. If you do not, already, have one, you can start from a DTM by creating a contour layer. Given the rest of the treatment, consider generalizing the contours. Otherwise a lot of patience will be needed…<\/p>\r\n\r\n\r\n\r\n

In order to obtain the Tanaka\u2019s contours, we will start by breaking down the polylines into elementary segments having only two points. For each segment we will calculate the angle of exposure to the light source. In function of this angle we will assign to each section a certain colour and \u00a0thickness : the sections completely exposed to the source, placed arbitrarily to the North West , will be white and thicker , the stretches perpendicular will be the finest, and the sections facing away from the light source will be completely black.<\/p>\r\n\r\n\r\n\r\n

To break polyline, we will use the Grass command \u00a0 v.split.vert that cuts the polylines at each node.<\/p>\r\n\r\n\r\n\r\n

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