DEMMETA

Description

DEMMETA adds the PCI standard digital elevation model (DEM)-related metadata tags to an existing DEM raster. Any existing metadata tags in the DEM raster may be overwritten during processing (see Details, later in this topic).

Parameters

Name	Type	Length	Value range
Input DEM *	String	1 -
Elevation layer	Integer	0 - 1
Background elevation	Float	0 - 1
Elevation reference	String	0 -	MSL | ELLIPS
Elevation units	String	0 - 1	METER | FEET | US_FEET
Elevation offset and scale	Float	0 - 2
Failure value	Float	0 - 1
Vertical accuracy	Float	0 - 1

* Required parameter

Parameter descriptions

Input DEM

The name of the DEM file to update with new metadata. When the file is read-only (or otherwise does not support writing metadata to it), a .pox file is created with the same base name as the input file. If for any other reason the required metadata tags cannot be written to the file or the .pox file cannot be created, processing stops, and an error message is displayed.

This parameter is mandatory.

Elevation layer

The input elevation channel. During processing, this channel is updated with the standard PCI DEM-related metadata tags.

This parameter is optional.

Background elevation

The background-elevation (NoData) value to use to update the NO_DATA_VALUE metadata tag of the DEM channel.

The legacy BACKGROUND_EVELATION metadata tag is discontinued. If it does exist in the DEM file, it is deleted and replaced during processing by the NO_DATA_VALUE metadata tag, even when you do not specify a value for the parameter. If this does occur, DEMMETA displays the following message: Warning: Deprecated BACKGROUND_ELEVATION (value -32768) tag found, it has been replaced with NO_DATA_VALUE.

This parameter is optional.

Elevation reference

The vertical reference for the elevation values in the DEM file you specify, and for the constant value of the Elevation offset and scale (ELFACTOR) parameter. The value you specify is used to update the ELEVATION_DATUM metadata tag of the DEM channel.

This parameter is optional.

Elevation units

The units of the elevation values stored as pixel values in the DEM file you specify. The ELEVATION_UNITS metadata tag will be updated with this value.

Elevation offset and scale

The value you specify for this parameter is used to update the ELEVATION_OFFSET and ELEVATION_SCALE metadata tags, and is used subsequently to shift and scale the DEM-pixel values. Usually these are set to reflect the Elevation units (ELEVUNIT) parameter.

You can specify up to two values for this parameter: the first defines the offset and, optionally, the second specifies the scale.

The conversion formula is as follows:

elevation_value = scale * (DEM_pixel_value + offset)
          

Failure value

The value you specify for this parameter is used to update the FAILED_VALUE metadata tag. It specifies the value given to pixels for which the generation of elevation values failed. The value should be outside the range of valid elevation values. The failure value identifies the areas that can be interpolated and filled.

Some DEMs contain only valid data. If this is the case with the DEM file you specify, you need not specify a value for this parameter. That is, it is not necessary to update the FAILED_VALUE metadata tag.

Vertical accuracy

The value you specify for this parameter is used to update the DEM_Z_ACCCURACY metadata tag on the input DEM. It specifies the vertical accuracy associated with the DEM, in meters.

Details

DEMMETA adds the PCI standard DEM-related metadata tags to an existing DEM raster. Any existing metadata tags in the DEM raster may be overwritten during processing.

That is, metadata tags can exist at the file and channel levels. If a tag exists at both levels, the value of the channel-level tag has priority, and is retained when you do not specify an input elevation channel. Any parameter that updates a metadata tag will overwrite any corresponding tags in the DEM raster. When no metadata tag is found, a new tag will be created at the channel level with the value you specify. When the input raster file has only one channel, all file-level metadata tags, and that are supported by DEMMETA, will be deleted, if they exist. When two metadata tags refer to the same information, such as NO_DATA_VALUE and BACKGROUND_EVELATION, the deprecated one will be deleted.