Pitney Bowes MapInfo Vertical Mapper - Manual (Page 132)

The Point Inspection Function
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Vertical Mapper 3.7
The Horizontal Distance is the “crow fly” distance from the beginning point of the transect line to the
indicated sample.
The True Distance (Elevation.grd) is the ground or “overland” distance from the beginning point of
the transect line to the indicated sample
Note Whenever a cross section line crosses a null area, the true distance is reset to zero.
The Point Inspection Function
The Point Inspection function updates a table of point data with a new column of values taken from
one or more geographically coincident grid files. The process inspects the grid file at each point,
returns the appropriate grid value, and writes the value to a new column in the point table. In many
ways, the procedure is the reverse of creating a grid from a set of points. An example would be
adding a column of income data to a point table of dwelling locations using a grid file of average
family income.
Using the Point Inspection Function
When you use the Point Inspection function, a new column is created in the point table for each
open and active grid that contains the respective grid value corresponding to each point location.
1. Open a MapInfo table of point data and the grid files from which the information is to be
extracted.
2. In the Grid Manager, click the Analysis button and choose the Point Inspection command.
3. From the Table to Update list in the Point Inspection dialog box, choose the appropriate table
containing the data points to be updated.
The Null Value edit box displays the value that will be used if the point lies off the grid or over a
null cell.
4. Click the OK button.
Note Values from all open and geographically coincident grids will be added as new columns to
the point table assuming that all grids are active.
The Line Inspection Function
The Line Inspection function displays several statistical parameters based on the grid values that a
specified line overlays, such as the average elevation of a runway. The grid is sampled at several
locations along the selected line. Each line is sampled a specified number of times regardless of the
line length (the default is 100 samples). Because the number of samples taken influences the final
results and each line is sampled the same number of times, statistics calculated for very long lines
may be less accurate than those calculated for shorter lines.
The way to get around this is to determine how long the longest line is and then base the sample
number upon that. As shown in the next figure, a simple MapInfo Professional SQL Query can be
performed to do this, and the number of samples can be modified in the Preferences dialog box.