Research on the method of making Hillshade in ArcGIS

Source: Internet
Author: User

  First, Data introduction

The data used in this paper is the national 30-meter resolution Aster DEM, the data volume size is 58G,WGS84 coordinates, the cell type is signed BIT INTEGER. NASA has published a global 30-meter resolution Aster DEM and is free to download.

  Second, Hillshade generation

We know that in ArcMap there are hillshade tools to generate Hillshade; ERDAS provides shaded relief tools; The ENVI hillshade tool is stored in the topographic modeling. We used the three software to generate the Hillshade, the results are as follows:

  

During the entire build process, ArcMap is relatively slow to work with large data raster images and is not ideal when working with a geographic coordinate system dem. In, we will find that there are a lot of bumps in the flat area; The Erdas effect is comparable to arcmap with a convex dot. Compared with the previous two, envi processing the fastest, the best results.

Combining the above analysis, using ENVI to generate Hillshade is the best choice. However, the ENVI processing of the resulting Hillshade file data size is about 120G, which is very detrimental to data transmission. How to reduce the amount of data?—— data compression.

 Third, data compression

As mentioned above, the ENVI processing generated a hillshade file data size of about 120G, nearly 1 time times larger than the original 58G! This is because the ENVI is stored with the three-BIT float cell type when generating the hillshade, so the amount of data is about twice times that of the original file.

As we all know, the most commonly used image compression algorithms are JPEG 2000,ECW and mrsid, but they cannot compress the image data of floating-point type. Therefore, before you compress a hillshade, you need to convert it to a format supported by the compression algorithm. Here, you can use the data export of ArcMap. Here's how:

1. Load Hillshade data into ArcMap, select the Symbology tab in the right-click properties of the layer, select stretched, set the stretch type to Min-max ... It is important to note that the invalid values must be ignored when the image data is being counted.

  

2, after setting, select the image layer right click, select Data-export Data, under Output raster, select Use Renderer, you can convert the image to the unsigned 8 BIT integer cell type storage.

By converting the cell type, the image file size is reduced to around 30G. On this basis, the MRSID compression, the final national 30 meters resolution of the Hillshade data size of 680M.

  Iv. Summary

Taking the national 30-meter resolution Aster dem as an example, this paper describes how to make a high-quality, small data volume of the mountain Shadow. By comparing the hillshade of the three software of ArcMap, Erdas and ENVI, it is determined that the highest quality of the hillshade produced by selecting Envi is the best, and the data compression technology is used to compress the Hillshade from the original 120G size to 680M to improve its browsing speed. On the other hand, it is easier to carry and transmit data, and it is better used in cartography and other related application fields. Figure 3 is a shaded relief map made from a hillshade product.

  

Research on the method of making Hillshade in ArcGIS

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