DEM files typically contain land XYZ information at a regular grid-spaced interval to represent ground relief.
In general, the DEM source data is contained in one section of the DEM file (Logical record type `A'), and the actual data (XYZ) information is contained in another part of the DEM file (Logical record type `B').
The following data, based on logical record type `A', is displayed for each DEM file that you add to a surface:
Element Name |
Corresponding Data Element Number in Logical Record Type ’A’ |
Details |
---|---|---|
Description |
1 |
The first 140 characters of a DEM file, which may include the file name and location. |
Estimated Point Total |
N/A |
The estimated number of points in the DEM file, rounded up to three significant digits. |
Coordinate System Type |
5 |
The ground planimetric reference system: UTM, State Plane, or Lat/Long. |
Zone |
6 |
Code that defines the zone in ground planimetric reference system. These can be found in Appendixes 2-E and 2-F of Standards for Digital Elevation Models. The Zone is meaningful only if Coordinate System Type is UTM or State Plane. |
Horizontal Datum |
27 |
The horizontal datum of the ground planimetric reference system, such as NAD27. |
Vertical Datum |
26 |
For more information, see Appendix 2-H of the Standards for Digital Elevation Models. |
Vertical Datum Shift |
31 |
The value is the average shift value for the four quadrangle corners obtained from program VERTCON. Autodesk Civil 3D adds this value to the vertical datum to convert to NAVD88. If the vertical datum is NAVD88, then the vertical datum shift value should be zero. |
DEM Level |
3 |
There are three possible DEM Levels:
|
X-Y Units |
8 |
The unit of measure for ground planimetric coordinates throughout the file, such as radians, feet, meters, or arc-seconds. |
Elevation Units |
9 |
The unit of measure for elevation coordinates throughout the file, such as feet or meters. |
Minimum Elevation |
12 |
The minimum elevation for the DEM. The value is the units of measure defined by Elevation Units. |
Maximum Elevation |
12 |
The maximum elevation for the DEM. The value is the units of measure defined by Elevation Units. |
X Spacing |
15 |
DEM spatial resolution for X values. The value is the units of measure defined by the XY Units. |
Y Spacing |
15 |
DEM spatial resolution for Y values. The value is the units of measure defined by the XY Units. |