ASCII XYZ Triples

Data Manipulation,  Import,  ASCII DEMs,  ASCII XYZ

Imported ASCII XYZ files can be in the following orders:

• Easting-northing-elevation (z value): UTM values
• Latitude-longitude-elevation: strictly speaking not XYZ order, but a common method.
• Longitude-latitude-elevation:
• Specialized Degree-Minute-Second format

Values must be separated with blank spaces, tabs, or commas.

Each triple must be on a line.

Latitude and longitude must be in decimal degrees. West longitude is expected to be negative, but you can multiply all longitudes by -1. You can also specify all longitude as positive, from 0 at the Prime Meridian, 180 at the date line, and values between 180 and 360 in the Western Hemisphere.

If the values are in rectangular, easting-northing, or UTM, they must be in meters.

The import will have the following steps:

• Select xyz file.
• Select options for reading file.  You can get either a grid or a database.   It will give you a point DB, which you can display as a continuous line, or convert to a line.
• If you want to create a grid, rather than a database.
  • The program will cycle through the data to determine the range for each value (x , y, and z).  There will be a progress count on the lower left in the status bar.
  • You will be placed into the header record editor. The key variables should be correctly set based on the type of data you selected for reading. You must carefully select the x and y spacings you desire in the grid. You can ignore other settings at this point, although you should set the units in your data set for xy and z values.
  • The program will force you to verify the x any y spacings.
  • The program will compute the number of columns and rows that will be in the data set, based on the data spacing you selected and the range of values in your input file, and ask you to verify the header file settings.
  • The program will interpolate the gridded data set.  It uses a drop in the bucket algorithm, putting each value at the nearest grid point.  Any values later in the file will overwrite earlier values.
  • The program will show you the resulting DEM, so that you can evaluate how well you chose the grid parameters, and how good the data coverage was.
  • You can fill in holes in the resulting grid using an option on the Edit menu of the data manipulation form.

This option is intended for the following cases:

• Grid that was exported into ASCII XYZ.  In this case you should recreate the original grid, using the same data spacing, and you should not have to fill in holes in the data set.
• Random triples and want to create a quick and dirty grid.  In this case you should set the grid spacing so that you have approximately one data point per grid cell, and you may have to fill in holes in the data set.
• It is a Hail Mary option, and requires that you understand something about the data you are trying to import.

Last revised 10/24/2019