Laserfiche WebLink
DIVISIO 2 MEMORANDUM <br />The procedure used to create the image base map for the study area is summarized as follows: <br />• Available USGS DOQQs, in GeoTiff format, were acquired for the study area. The dates of <br />these DOQQs range from 1993 to 2001. In addition, the USGS was contracted under cooperative <br />agreement by CWCB, to update 76 DOQQs from 1998. <br />• All of the imagery was mosaicked and compressed into MrSID format. The image was then <br />broken into 4 seamless tiles for ease of distribution and storage (Figure 2.0). <br />• Due to the large size of the study area and the high resolution of the Image Base Map data, a <br />compression technology was selected to reduce the data files to manageable sizes. The MrSID <br />compression format, a technology of LizardTech, Inc. of Seattle, Washington, was chosen for the <br />image compression. MrSID provides a 15:1 compression ratio for grayscale imagery while <br />maintaining geometric accuracy. The image base map was made from the Generation 2 MrSID <br />format. MrSID files can be used in ArcExplorer, ArcView 3.x, and ArcGIS 8.x. The <br />compressed imagery can be viewed with these software packages by simply adding the data as <br />with any other GIS data layer. In ArcView 3.x, the MrSID Image Support extension must be <br />checked "on ". The extension is included with standard ArcView 3.x software. <br />Page 8 of 23 PRiverside Technology, inc. <br />Water Resources Engineering and Consulting <br />Table 6.0 Years of Source Imagery Used by USGS to Produce DOQQs <br />