Exporting Shapefile with dBm Units
Q: How can I export a shapefile of a TAP coverage so I can import received power levels (in dBm) into other mapping software?
A: With TAP6.0.2384 or later and a Maintenance Subscription date of April 30, 2011, or later, you can add the dBm received power values to a shapefile created by the TAP HDCoverage function.
Note that all values in this example are for demonstration purposes only. You should determine appropriate settings for your application.
The Terrain Analysis Package (TAP)™ area coverage calculations are computed in values of field strength (in dBu) rather than values of received power (in dBm). The dBu values provide more flexibility and are not a function of the mobile receiver hardware, local environmental conditions such as varying body loss values, etc. The use of dBu and dBm values is discussed in the Level dBm Increments in HDMapper™ article. The computed dBu values can be shown in TAP as the corresponding dBm power values (for a particular mobile configuration) also as described in that article.
It is sometimes useful to draw the coverage computed in TAP using other mapping software. Since TAP uses industry-standard files in the ESRI Shapefile (.SHP) format, importing the files into most other mapping or GIS software is very convenient. However, the native units of the field strength in the shapefiles created by TAP are dBu.
The feature described in this article enables you to add a data value for the dBm received power value for each computed location (in a Tile or Radial study) so that you can select that data field for plotting in third-party mapping software. The field strength values (in dBu) are converted to the corresponding received power values (in dBm) and written to the shapefile database.
After you have computed the study with HDCoverage, click on the TAP6 “Area” menu and select “Export dBm to Shapefile”
When the list of coverage study Tasks is displayed, pick the study you want to export:
The shapefile database file (.dbf) will be modified to include a data field (named “DBM_VAL”) with the computed dBm values.
You will have the option to open the folder where the TAP coverage shapefiles are saved (in the MAPPING folder where TAP is installed):
You can click the “Yes” button to open the folder.
The original shapefile database file has been saved with the year, month, day and time appended to the file name. This file is not used but is saved in case of problem with the new database file.
The three components of the shapefile layer (.SHP, .SHX, .DBF) can be copied and used in other mapping software
The shapefile can still be used in TAP. The other files that may be in the folder (.SMF, .TXT, etc.) are only used by TAP and are not needed (or recognized) by other shapefile software.
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Copyright 2011 by SoftWright LLC
