A primary and secondary DEM can be configured. Their usage is controlled by the profile generation options under Configure - PL50L options -Terrain data. If both primary and secondary databases have been configured and are checked in the options, the program will start with the primary database. If the operation (profile or elevation backdrop) is not complete, then the secondary database will be used to fill in the missing sections. Therefore, the primary data base should have the best resolution.
The default and recommended setting is to use the primary DEM only. If the operation fails then it is a simple matter to check the secondary DEM and the user can inspect the different areas in which this DEM was used.
When a profile is first generated for the first time, the DEM file usage is written to the notepad.
Note that it is possible to configure a DEM with different data sources provided that they are both in the same database category and are referenced to the same datum. For example, in the BIL geographic database, one could load the GTOPO30.ndx index file and then add SRTM files to the index. The program would always use the SRTM file (the best resolution) if available.
The following sections provide the setup procedures for the various database formats supported by the program.
On completion of the setup procedure, generate a path profile in the terrain data section of the program. The site coordinates must be within the south-north and west-east edges of the DEM file. In the case of the BIL projected database, the following default DEM parameters may need to be changed based on the results of a test profile. In the primary or secondary DEM tab, click the File index button and then select Edit - Parameters or right click on a data cell
· byte order - change from Motorola-Spark to Intel or vice versa if the elevations are missing or erratic
· file origin - change the origin from the SW corner to the NW corner or vice versa if the elevation backdrop appears to be upside down
· treat no data values as sea level - use this setting if elevations are missing when a portion of the profile is over water. The missing values will be replaced by 0 elevations.
BIL projected DEM setup procedure
Use this option for Planet type data and ESRI GRIDASCII projected data. Select the primary or secondary DEM tab and then select the BIL projected data format from the digital elevation model drop down list. The basic setup procedure is described below:
· Set the datum and projection for the data source. All data files used in this database selection must be referenced to this datum.
· Click the Setup button and set the main directory for the DEM files.
· Click the File index button. Depending on the specific DEM format, the following options are available to import an index from external files. Select Files - Import Index.
For Planet type databases, select "text file index" item. This uses the standard text file import utility described in the general program operation section
For ESRI Arc Info/Grid BIL files, select the "bil, hdr, blw files" item and load any file with these suffixes. Note that the windows file open dialog includes an option to include the specific directory in the index.
If the DEM files are previously converted GRIDASCII files, then select the "GRIDASCII utm files" and multi select the DEM files. Note that the file suffix "utm" means that this is a projected DEM as opposed to a geographic DEM. The actual projection is not necessarily UTM.
The File index includes a conversion utility from ERSI GRIDASCII to a binary format. Select Convert - GRIDASCII and multi select the files to be converted. Note that the windows file open dialog includes an option to include the specific directory in the index
BIL geographic DEM setup procedure
Use this option for ESRI GRIDASCII geographic data. Select the primary or secondary DEM tab and then select the BIL geographic data format from the digital elevation model drop down list. SRTM, NED and GTOPO39 DEMS are examples of the BIL geographic DEM. Preconfigured options for these databases are available. The basic setup procedure is described below:
· Set the datum corresponding to the data source. All data files used in this database selection must be referenced to this datum. Set the projection to geographic (latitude-longitude)
· Click the Setup button and set the main directory for the DEM files.
· Click the File index button. Depending on the specific DEM format, the following options are available to import an index from external files. Select Files - Import Index.
For ESRI Arc Info/Grid BIL files, select the "bil, hdr, blw files" item and load any file with these suffixes. Note that the windows file open dialog includes an option to include the specific directory in the index.
For SRTM hgt files, a file open dialog is used to multi select the hgt files. The index will be created using the file name for the extents and the file size for the resolution.
If the DEM files have been previously converted GRIDASCII files, then select the "GRIDASCII geo files" and multi select the DEM files.
The File index menu includes a conversion utility from ERSI GRIDASCII to a binary format. Select Convert - GRIDASCII and multi select the files to be converted. Note that the windows file open dialog includes an option to include the specific directory in the index
NED (CONUS) setup procedure
This is a specific implementation of the BIL geographic DEM. The term CONUS refers to the 48 contiguous states. The BIL file has the following characteristics:
· the data origin is the north west corner.
· data format can be 16 bit integers or 8 bit integers depending on the elevation range in the file
· byte order is big-endian (Motorola)
· the spacial reference is geographic with a resolution of 1, 1/3 and 1/9 arc seconds. The datum is NAD83. Spacial details are given in external ESRI blw and hdr files
Select the primary or secondary DEM tab and then select the NED (CONUS) data format from the digital elevation model drop down list. The datum is automatically reset to NAD 83 using a geographic (latitude - longitude projection).
· Click the Setup button and set the main directory for the DEM files.
· Click the File index button. The following options are available to import an index from external files. Select Files - Import Index.
For ESRI Arc Info/Grid BIL files, select the "bil, hdr, blw files" item and load any file with these suffixes. Note that the windows file open dialog includes an option to include the specific directory in the index.
If the DEM files have been previously converted GRIDASCII files, then select the "GRIDASCII geo files" and multi select the DEM files.
NED (Alaska) setup procedure
This is a specific implementation of the BIL geographic DEM for Alaska. The BIL file has the following characteristics:
· data is referenced to the center of a cell
· data is organized in rows running from west to east starting in the north west corner.
· the data format is a 16 bit integer
· byte order is big-endian (Motorola)
· the spacial reference is geographic with a resolution of 2 arc seconds. The datum is currently NAD27. Spacial details are given in external files ESRI blw and hdr files
Select the primary or secondary DEM tab and then select the NED (Alaska) data format from the digital elevation model drop down list. The datum is automatically reset to NAD 27 using a geographic (latitude - longitude projection).
· Click the Setup button and set the main directory for the DEM files.
· Click the File index button. The following options are available to import an index from external files. Select Files - Import Index.
For ESRI Arc Info/Grid BIL files, select the "bil, hdr, blw files" item and load any file with these suffixes. Note that the windows file open dialog includes an option to include the specific directory in the index.
If the DEM files have been previously converted GRIDASCII files, then select the "GRIDASCII geo files" and multi select the DEM files.
SRTM (World) setup procedure
SRTM data provides 3 arc second world wide coverage in the latitude range 60°N to 60°S. One arc second data is available for the United States. The data is available in ESRI BIL format and in 1 degree by 1 degree hgt files. This is a specific implementation of the BIL geographic data format with the following characteristics.
· the data origin is the north west corner.
· data format can be 8 or 16 bit integers in the ESRI BIL format. The hgt files use 16 bit integers.
· byte order is big-endian (Motorola)
· the spacial reference is geographic. The datum is WGS84. Spacial details are given in external files in the ESRI BIL version and are derived from the file name
Select the primary or secondary DEM tab and then select the SRTM (World) data format from the digital elevation model drop down list. The datum is automatically reset to WGS 84 using a geographic (latitude - longitude projection).
· Click the Setup button and set the main directory for the DEM files.
· Click the File index button. The following options are available to import an index from external files. Select Files - Import Index.
For ESRI Arc Info/Grid BIL files, select the "bil, hdr, blw files" item and load any file with these suffixes. Note that the windows file open dialog includes an option to include the specific directory in the index.
For SRTM hgt files, a file open dialog is used to multi select the hgt files. The index will be created using the file name for the extents and the file size for the resolution.
If the DEM files have been previously converted GRIDASCII files, then select the "GRIDASCII geo files" and multi select the DEM files.
GTOPO30 (World) setup procedure
The GTOPO30 DEM provides world wide coverage with a 30 arc second resolution. This is a specific implementation of the BIL geographic data format with the following characteristics.
· data is organized in rows running from west to east starting at the north west corner.
· data format is 16 bit integers
· byte order is big-endian (Motorola)
· the spacial reference is geographic with a resolution of 30 arc seconds. The datum is WGS84. Spacial details are predefined in the program
Select the primary or secondary DEM tab and then select the GTOPO30 (World) data format from the digital elevation model drop down list. The datum is automatically reset to WGS 84 using a geographic (latitude - longitude projection).
· Click the Setup button and set the main directory for the DEM files.
· Click the File index button. Note that the complete index is automatically set The following options are available to add additional file indexes from external files. Select Files - Import Index.
For ESRI Arc Info/Grid BIL files, select the "bil, hdr, blw files" item and load any file with these suffixes. Note that the windows file open dialog includes an option to include the specific directory in the index.
For SRTM hgt files, a file open dialog is used to multi select the hgt files. The index will be created using the file name for the extents and the file size for the resolution.
If the DEM files have been previously converted GRIDASCII files, then select the "GRIDASCII geo files" and multi select the DEM files.
DTED setup procedure
DTED (Digital Terrain Elevation Data) is the US Defense Mapping Agency binary terrain data format. The basic DTED data format is given below:
· data is written in columns from south to north starting in the south west corner. each column begins with a header and ends with a check sum of the elevations.
· the elevation data is defined at the intersection of the row column grid lines
· data format is a 16 bit integer
· byte order is big-endian (Motorola)
· the datum is WGS84. the spacial reference is geographic. The east - west resolution is 3 arc seconds DTED level 1 and 1 arc second for DTED level 2. The north - south resolution varies with latitude as shown below for DTED level 1 data
0 to 50° - 3 sec 50° to 70° - 6 sec 70° to 75° - 9 sec 75° to 80° - 12 sec 80° to 90° 18 sec
Select the primary or secondary DEM tab and then select the DTED data format from the digital elevation model drop down list. The datum is automatically reset to WGS 84 using a geographic (latitude - longitude projection). The basic setup procedure is given below:
· Click the Setup button and set the main directory for the DEM files. This will depend on the selected directory structure as described below
· DTED files can be indexed using the main default directory or individual directories for each file. Another option is to used a defined directory structure and a file naming convention for these file. In the following arrangements the file name suffix is dt1 for level 1 data and dt2 for level 2 data.
USDMA defined directory names are based on the longitude e.g W072. File names in that directory are based on the latitude e.g. N34.dt1. In this arrangement the file would be (main directory)\W072\N34.dt1.
Canadian DTED file naming convention - this is the same as the USDMA convention with four zeros added to the directory and file names. The file name in this case would be (main directory)\W0720000\N340000.dt1.
the Pathloss version 4.0 file naming convention uses the latitude and longitude e.g. W072n34.dt1. The file name is unique and does not depend on the directory name. The files can be all located in a single directory or can be saved in a user defined data structure based on latitude or longitude. Using the directory format specifier "%x%03X" the file name would be (main directory)/W072/W072N34.dt1
· USGS 1:25000 ASCII DEM files can be converted to the DTED file format. This can be carried out from the Setup dialog or the File index. In the file index, the conversion will automatically create an index.
· If the file index method is used, click the File Index button. The select the Files - DTED file index menu item. Mu lit select the DTED files to create the index
CDED (Canada) setup procedure
CDED (Canadian Digital Elevation Data) files are provided in the USGS 1:250 000 ASCII DEM file format. These are available in a 3 arc second resolution for 1:250 000 scale mapping and 0.75 arc seconds for 1:50 000 scale mapping. The files are converted to a DTED file format with the suffix "dtd". The basic format is shown below:
· Data is written in columns from south to north starting in the south west corner. Each column begins with a header and ends with a check sum of the elevations.
· the elevation data is defined at the intersection of the row column grid lines
· data format is a 16 bit integer
· byte order is big-endian (Motorola)
· The datum is NAD83
· The the spacial reference is geographic (latitude - longitude). The grid spacing is based on the coordinates at a maximum and minimum resolution of 0.75 and 3 arc seconds for the 1:50 000, and 3 and 12 arc seconds for the 1:250 000 respectively, depending on latitude.
Select the primary or secondary DEM tab and then select the CTED (Canada) data format from the digital elevation model drop down list. The datum is automatically reset to NAD83 using a geographic (latitude - longitude projection).
· Click the Setup button and set the main directory for the DEM files.
· Click the File index button. Then select the Files - DTED file index and multi select the DTED files. The index lines will be created based on the file header information.
· The ASCII CDED files must be converted to the DTED format to be used in the program. In the File index select the convert menu item. Multi select the CDED files and the conversion will automatically generate the index for the converted files.
USA 3 sec compressed setup procedure
Three arc second terrain data for the United States in a compressed format is available for use with the Pathloss program. This data has been taken directly from the USGS 1:250,000 ASCII DEMs. The elevations in these files are in meters relative to mean sea level. The south-north resolution is 3 arc seconds. Below 50° the west-east resolution is 3 arc seconds. Between 50° and 70° the resolution is 6 arc seconds and 9 arc seconds above 70°.The error checking on these files consisted of the following verifications.
· Each elevation must be within the range specified for both the entire file and the specific column.
· The absolute value of all elevations including the maximum and minimum values must be less than 10000 meters.
A total of 29 files did not pass this criteria and these were edited. The majority of errors involved the maximum elevation in the file. Other errors included extreme elevations (-32467) at the end of columns. These files have all been edited. None of the changes involved interpolating elevations. Most of the errors occurred at sea level.
All files are contained on a single CD-ROM and are organized in directories based on longitude under a main directory 3SEC_USA. The directory names are based on the longitude of the southwest corner of file e.g. W095. The file names are based on the longitude and latitude of the southwest corner. At latitudes less than 50º, the files have been split into two halves at the central longitude of the file. The letter L (left) or R (right) is appended to the file name. The file suffix is always cte (compressed terrain elevations). As an example, the file W095N44R.CTE represents the western half of the one degree block whose southwest corner is located at 44º north and 95º west. The file is located in the directory 3SEC_USA\W095 on the CD-ROM. The basic setup procedure is given below:
Select the primary or secondary DEM tab and then select the USA 3 sec compressed data format from the digital elevation model drop down list. The datum is automatically reset to WGS84 using a geographic (latitude - longitude projection).
· Click the Setup button and set the main directory to the location of the 3SEC_USA directory.
· As this database uses a file naming convention in a fixed directory structure, a file index is not used and the setup procedure is complete
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