ASCII XYZ Triples
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.
- 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
- 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