/****************************************************************************
 *   gdem.h : 
 *   		header file for USGS DEM file reader class.
 *
 *   Change Log :
 *		 Feb 22, 1999 Initial version,  Liujian Qian
 *
 *   $Id: gdem.h,v 1.1 1999/02/23 04:27:55 qian Exp $
 ***************************************************************************/
#ifndef _GDEM_H_
#define _GDEM_H_

#include "gadt_grid.h"

/**
 * GDem 
 */
class GDem : public GGridDriver
{
public:
    int		open		(const char* ) ;
    
    const char* fileFormat	() {return "USGS-DEM"; }
    void	fillGridMeta	(GGridMeta& meta) ;
    void	customHeader	(void*& cust_hdr, int& len) ;
    int		numColumns	() ;
    int		numRows		() ;
    int		numBands	() ;
    float	ignoreValue	() ;
    
    void	scanline	(void* buf, 
        			 int row, 
        			 int col_begin=-1, int col_end=-1) ;
    void	area		(void* buf,
        			 int row_begin, int row_end,
        			 int col_begin, int col_end);
    int		close		() ;

};




/*
DEM--Digital Elevation Models

    The U.S. Geological Survey produces five primary types of digital elevation model data. 
    They are: 

    7.5-minute DEM (30- x 30-m data spacing, cast on Universal Transverse Mercator (UTM)
    projection or 1- x 1-arc-second data spacing). Provides coverage in 7.5- x 7.5-minute 
    blocks.  Each product provides the same coverage as a standard USGS 7.5-minute map 
    series quadrangle. Coverage: Contiguous United States, Hawaii, and Puerto Rico. 

    1-degree DEM (3- x 3-arc-second data spacing). Provides coverage in 1- x 1-degree blocks.
    Two products (three in some regions of Alaska) provide the same coverage as a standard 
    USGS 1-x 2-degree map series quadrangle. The basic elevation model is produced by or 
    for the Defense Mapping Agency (DMA), but is distributed by USGS in the DEM data record
    format.    Coverage: United States. 

    30-minute DEM (2- x 2-arc-second data spacing). Consists of four 15- x 15-minute DEM
    blocks. Two 30-minute DEMs provide the same coverage as a standard USGS 30- x 60-minute
    map series quadrangle. Saleable units will be 30- x 30-minute blocks, that is, four 15- x
    15-minute DEMs representing one half of a 1:100,000-scale map. Coverage: Contiguous
    United States, Hawaii. 

    15-minute Alaska DEM (2- x 3-arc-second data spacing, latitude by longitude). Provides
    coverage similar to a 15-minute DEM, except that the longitudinal cell limits vary 
    from 20 minutes at the southernmost latitude of Alaska to 36 minutes at the northern 
    most latitude limits of Alaska. Coverage of one DEM will generally correspond to a 
    1:63,360-scale quadrangle. 

    7.5-minute Alaska DEM (1- x 2-arc-second data spacing, latitude by longitude). Provides
    coverage similar to a 7.5-minute DEM, except that the longitudinal cell limits vary 
    from 10 minutes at the southernmost latitude of Alaska to 18 minutes at the northernmost
    latitude limits of Alaska. 
*/


#endif



Documentation generated by lqian@lqian-sun on Wed Jul 14 09:36:10 EDT 1999