數值地形的彩繪明暗製圖及應用

Color Shading of a Digital Terrain Model and Its Application

李錫堤(C. T. Lee)

《地工技術》 56期 (1996/08) Pp. 69-78

https://doi.org/10.30140/SG.199608.0006

摘要

規則網格數值地形模型基本上具有與影像圖類似的資料結構，只要將高程值轉換成灰度值，就可以產生一幅影像檔，並可以在一般的影像軟體下，顯示地形的高低起伏。若再考慮日照明暗度的效果，則可進一步加強影像的立體感與真實感。類似這樣的具有明暗效果的影像圖一般稱之為明暗圖。若在做高程值對灰度值轉換時，採用三原色對應關係及彩色影像格式，則成圖即為彩色，而這樣的影像圖則稱之為彩繪明暗圖。一張彩繪明暗圖一般為一張平面圖，若加以透視投影，也可以是一張三維的透視圖。本文介紹數值地形模型的資料結構，彩繪明暗圖的製圖原理，並舉例說明彩繪明暗圖在地質判釋上的應用。由於電腦處理技術可以透過不同的日照方向、不同的觀看方向、不同的顏色值給予以及不同的高度值垂直誇張倍率等選擇，以突顯地形的特徵，可以提高地質判釋的正確性，所以是一種值得推薦的方法。

關鍵字

明暗圖 ； 彩繪明暗圖 ； 數值地形模型

並列摘要

A regular grid digital terrain model(DTM) has similar data structure as a raster image. Only a simple transformation from elevation value to gray value is needed to produce an image file which may be shown by an image viewer software. If we further add the effect of shade, then we may enhance the stereographic effect of the image and represent the topography in a more realistic way. An image map of this kind is called a shading map. If color values are considered in the elevation to color transformation, then a color shading map may be got. A color shaded DTM may also be shown as a perspective projection, if a projection technique is used.This paper firstly describes the data structure of a DTM, then color shading method, and finally some examples to demonstrate the application of a color shaded DTM in geological investigation. Because the use of a digital computer is easy to change the selection of sun position, eye position, vertical exaggeration of elevation height and various assignment of colors, so, interested features can be emphasized according to proper selection of the parameters. It is helpful for us to make geological interpretation from an enhanced image. Accordingly, DTM color shading technique is useful and is worth being recommended for use.

並列關鍵字

shading ； color shading ； hill shading ； relief shading ； digital terrain model ； digital elevation model