Digital Elevation Model's and some Three-dimensional Display Capabilities of ER Mapper Software

by :  Idung Risdiyanto

        MIT Student / Biotrop

        1999

Brief Explanation

            Digital Elevation Models are representation as a regular grid of numbers. The spacing between grid elements represents the interval between samples. The numerical value in each grid element represents the elevation at that point. This is often a floating-point number, to ensure that small variations in elevation can be record accurately.  If we use the software image processing especially the ER Mapper software, we can be displaying or view the DEMs into the 2D and 3D prespective mode.  The differences between 2D and 3D are used the layer in the algorithm window.  If we want to create DEM into 2D mode, we often use the intensity layer and then put the DEM dataset into this layer.  The intensity layer is the key to the colordraping technique. Using the intensity layer in the algorithm window will be influencing the brightness (or intensity) of the image, colors are automatically control by the data loaded into the Intensity overlay. If we want to create the DEM viewing into 3D mode, we need the height layer.  However, if its layer do not available in the software, we can use the intensity layer. Height layers are using in 3-D images. Any dataset can use in a height layer including the intensity layer. In the ERMapper software, the 3D perspective takes a standard algorithm. The manual tutorial give us the recommendation to use the height layer if we want to create the DEMs model into the 3D viewer and put the DEM dataset into this layer.  When we use the 3D perspective viewer we can select many option viewing for make the image will be great or satisfaction depend on the our purpose or goal.  In the algorithm window we can select and create the option for viewing if we want.  In this below will be explanation about the sheet of 3D View in the algorithm window and the display effect if we change the option.  In this sheet we can choose one of four the draw mode :

Texture draw mode:  The 3D image will be presented the texture of surface and if we see and compare with the composite image before add the height layer we will found that the texture draw mode do not change the color of image.  For example, the green color (vegetation) the highland (Halimun peak) and the its forest do not change or the sun angle do not influence the image like as if we use do-sunshading.

Wireframe draw mode: The image can be quickly displaying.  The wire frame can consist of horizontal (H), vertical (V) or both horizontal and vertical (HV) lines.  But, sometimes the display not clearly because the viewing generate is quickly and building the line by line in each of pixel to be contained the floating point. 

Smooth shaded draw mode :  Similar as the 2D shaded relief, but in this the viewer is the 3D perspective.  The image has the some part is dark and some part is light.  Therefore we use the composite (RGB 741) image as the base, so, the color image will be changes become darker or lighter.

Based on the choosing of the draw mode and memory of computer capability, we can make the detail viewer and see the vector layer more clearly, we can increase the terrain detail that we want.  We also make the bounding box using bounding box check in the 3D view list.  If we use it, the 3D image will be put into the transparent box and may be will help us to know the border or limit axis of the area on the image.

            The others options to change the viewer can we select from the others sheet in the algorithm window.  For example, from the 3D properties we can get the information about the z scale and z offset and the others.

            Last one, the 3D viewing can use for understanding how the real surface on the earth if we see from the image.  Using 3D viewing we also can change the direction of the see or our eyes so that we can know what happened or the reality if we see from other direction.  For application, 3D viewing is very important for the train of the pilot, especially for the sky acrobatic use the jet plane or fighter plane.  Using the 3D simulator of the earth surface, the pilot will be train and learn how to controlled the plane if it is scrolling or others maneuver or acrobatic moves.

These are few example of the result this assignment :

3D Perspective