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Geodata Overlay Viewer (GOVu): An innovative way to handle high-resolution imagery
Satya Priya & Puneet Sharma
RMSI Private Limited, A - 7 Sector 16, Noida 201 301, India
Tel: +91 120 251 1102, 251 2101, Fax: +91 120 251 1109, 251 0963
Introduction
A compressed image is one that has been compressed to reduce the image file size, while still providing an almost perfect version of the original. The most effective technique is the wavelet based technique, which is a method of processing, quantizing and then encoding the image in a way that results in very high levels of compression, with an almost perfect reconstruction of the original image.
Typically a color image such as an airphoto can be compressed to less than 2% to 5% of its original size (50:1 to 20:1 compression ratio). This means that, at 20:1 compression, 10GB (10,000MB) of color imagery will compress down to 500MB, which is small enough to fit on to a single CD-ROM. Where the source image has less information, such as scanned topographic maps or airphotos over areas with less land change, higher compression rates may actually be achieved. 100:1 or more is not uncommon for compressed scanned topographic maps. Because the compressed imagery is
constructed of multi-resolution wavelet levels, one can enjoy fast roaming and zooming on the imagery - even from a comparatively slow media such as CD-ROM.
The Geodata Overlay Viewer (GoVu) is an application used to view imagery with a custom file format‚ *.gov™. Along with the basic navigational functionalities of zooming, panning etc., the Geodata Overlay Viewer provides additional functionalities like Export, Print, Lens, Telescope, Merge, Blend, Gazetteer, Index Map, Vector Overlay, Properties and Snapshot. Some of these additional functionalities are described below in detail.
Highlights of the Viewer developed:
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Creation of the GoVu format
- Creation of the GoVu image-maker that combines compressed ECW/MrSID raster, meta data of the image, the index map and the respective projection information
- Demonstration of some unique functionalities
The RMSI Image Maker is an application used to make imagery in a custom file format ‘.GOV’. The technology used to develop Image viewer is built using MFC classes without any support of outside controls. However, MrSID1 and ECW2 decompression SDKs are used for image rendering. Supported Formats - ECW and MrSID encrypted inside GOV format. Inputs: MrSid or ECW file Bitmap of the Index map (Optional) (1MrSID is a registered format owned by LizardTech plc. 2ECW is a registered format owned by ER Mapper Inc.)
Inputs required for creating GoVu format:
MrSid or ECW file, Bitmap of the Index map (Optional), Meta Data of the image (Optional). Projected Top Left Coordinate and Resolution of the image in any of the following units (Meter, Kilometer, Feet, Centimeter, Inches, Miles, Yards), and Projection system of the image.
Image: Here users enters the projected Top Left Coordinate and Resolution of the image and on the bases of the same application calculates the bottom right coordinates of the image and top, left, bottom right coordinates of the index map.
Metadata: Here user can view the meta data user has attached with the file. You can attach meta data using option provided in the viewer.
Projection: User can choose the projection system in which he/she has projected the image. This is as such not used anywhere in the system it is just for the information of the user.
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