WMS:DEM Files

DEM files are used for storing DEMs processed by WMS. After clipping, thinning, or smoothing an imported DEM you may wish to save it to a WMS formatted file so that it can be recalled later without having to perform the same processing steps. The DEM file format is shown in Figure 1 and a sample file is shown in Figure 2.

DEM	/* File type identifier */
ORIGIN xlowerleft ylowerleft	/* Southwest coordinare of DEM */
DELTAX deltx	/* X spacing of elevation points */
DELTAY delty	/* Y spacing of elevation points */
ELEVATIONS ncol nrow	/* Number of columns and rows in DEM */
z11	/* elevation of row 1 column 1 */
z21	/* elevation of row 2 column 1 */
z31	/* elevation of row 3 column 1 */
.
.
.
zncol,nrow	/* elevation of row nrow column ncol */

Figure 1. DEM File Format.

DEM
ORIGIN 1000.0 1500.0
DELTAX 30.0
DELTAY 30.0
ELEVATIONS 450 300
101
104
.
.
250

Figure 2. Sample DEM File.

The cards used in the DEM file are as follows:

Card Type	DEM
Description	File type identifier. Must be on first line of file. No fields.
Required	YES

Card Type	ORDER
Description	Defines the order in which elevations are read in.
Required	NO (By default row major starting in upper left corner is assumed)
Format	ORDER ordertype
Sample	ORDER 0
Field	Variable	Value	Description
1	xlowleft	0-3	0 - Elevations start at upper left, one row at a time. 1 - Elevations start at upper left, one col. at a time. 2 - Elevations start at lower left, one row at a time. 3 - Elevations start at lower left, one col. at a time.

Card Type	ORIGIN
Description	Defines the lower left (southwest) coordinates for the DEM.
Required	YES
Format	ORIGIN xlowleft ylowleft
Sample	TNAM 1000.0 1500.0
Field	Variable	Value	Description
1	xlowleft	±	Lower left X coordinate of the DEM
2	ylowleft	±	Lower left Y coordinate of the DEM

Card Type	DELTAX
Description	The X spacing between DEM points.
Required	YES
Format	DELTAX deltx
Sample	DELTAX 30.0
Field	Variable	Value	Description
1	deltx	+	X spacing of DEM points.

Card Type	DELTAY
Description	The Y spacing between DEM points.
Required	YES
Format	DELTAY delty
Sample	DELTAY 30.0
Field	Variable	Value	Description
1	deltx	+	Y spacing of DEM points.

Card Type	ELEVATIONS
Description	Elevations for the DEM.
Required	YES
Format	ELEVATIONS ncol nrow
Sample	ELEVATIONS 450 300 101 104 . . . 98
Field	Variable	Value	Description
1	ncol	+	Number of columns.
2	nrow	+	Number of rows.
3-n	z	+	Elevations of DEM points.