Defining the import fields is the fourth and final step in the process of importing ASCII files. Once you have defined how to separate each field using delimiter or fixed widths, each field must be mapped to an attribute of the LIDAR point. The text files must have a minimum of X, Y, and Z fields. The other fields such as intensity, classification, etc. are optional. If the text files contain data that is not used by the LIDAR points, the fields can be ignored by specifying them as Unknown.

Forcing Points to a Classification

If all of the points within the files you are importing belong to a particular classification such as Ground, those points can be forced to a classification during the import process. This is particularly useful for batch importing ASCII files that were delivered by the service provider as a set of bare earth and/or first return files.

Importing to a specific LAS File Version

You have the choice to select one of several LAS file versions to create. Not all fields can be imported for each file version. For example, the Red, Green, and Blue color fields can only be imported when 1.2 is selected. Versions 1.0 and 1.1 do not define fields for color values in the point records.

In addition to selecting the LAS file version, you will also be displayed the point record format that will be used in the LAS File. The point record format is chosen based on the set of fields to import from the text files. To learn more about the LAS file format, versions, and the different point records, go to www.asprs.org/LAS_Specification.

Importing Color Values

The storing of color values within point records are supported in the LAS File version 1.2 and above. The color values are stored as 16-bit components, or are based on a 48-bit color system. Color values that are based on a 24-bit color system (i.e., 8-bits per component, values between 0 - 255) are translated to the 48-bit color system within the LAS File. If at least one color value exceeds the 255 value limit, the values are not translated but are stored in the LAS File as they appear in the text file.

Learn more about the ASCII Preview Window

Step 4: Defining the Fields to Import

Defining Field Types, Importing Points to Classification, and Selecting LAS File Version

1. Complete Steps 1 through 3 of the ASCII file import process if you have not already done so. See ASCII Import Wizard for the list of steps.

2. On the Step 4 page, click a field or column in the Columns list, then select the correct point attribute option on the right to assign it to the selected column. The ASCII Preview Window will update and display the selected field with the same heading.

   

3. Select the next column in the list and continue assigning columns to point attributes until all fields or columns that are to be imported are assigned their correct point attributes.

4. Click the arrow on the LAS File Version box, then select the desired file version for importing the text files. See the "About Defining the Fields to Import" section above for information about the different LAS file versions. 

   Note  A warning may appear if you select fields that a file version does not support. You can cancel the selection or continue and set the unsupported fields to Unknown.

   

5. Click the Force all points within all files to classification check box if all of the points in the files being imported belong to a particular classification.

   

6. If you selected Force 100% Resolution, select the classification that the points belong to in the drop-down menu that appears.

   

7. Click Finish to start the import process.