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Problem: LAS dataset disappears in ArcMap if the projection of the data frame is changed

Description

If the projection of the ArcMap data frame is changed, some or all the features in the LAS dataset disappear.

Cause

While the LAS dataset (LASD) has a projection defined, the LAS files which are loaded into the LAS dataset do not have projections defined.

Solution or Workaround

The LAS file specification specifies the file must have the spatial reference information written to the file header. However, this requirement is not always followed.

This information appears on page 3, Section 4, in the 3rd paragraph under 'LAS FORMAT DEFINITION' in the LAS Specification Version 1.4 - R13 15 July 2013 document.

There are two methods that can be used to determine if a LAS dataset has a projection defined.

• Run the CheckLAS tool, which is available here. The utility checks the validity of the LAS file, and sees if the LAS file has a defined projection.

• Use ArcCatalog to determine the spatial reference.

1. Open ArcCatalog, right-click the folder where the LAS dataset is to reside, and create the new LAS dataset.
2. Select the General tab, and check the box labeled, "Store relative path names to data sources".
3. Right-click the new LASD file, select Properties, and select the LAS Files tab.
4. Add the new LAS files to the LAS dataset. At the end of each line, click the ellipsis (button with the three dots).
5. On the General tab for the LAS file, the spatial reference is viewable in the upper left corner of the dialog.

If <No projection> is displayed, and the file is imported to the LAS dataset anyway, display problems are likely with the data because the software does not have a projection definition for the LAS files within the dataset.

This causes the data to disappear when the projection of the ArcMap data frame is changed, since data with no projection defined cannot be projected on-the-fly.

There are two methods to create or apply a projection to the LAS files to work around this problem. If the LAS file does not have an assigned projection definition, the user can employ the LAS custom tools, which includes the Create PRJ for LAS tool.

Another solution is to write a copy of the correct projection definition to 'Favorites' in ArcMap.

1. In ArcMap, go to View > Data Frame Properties > Coordinate System tab.
2. Select the correct projection from the available options, and click the 'Add to Favorites' button.
3. Navigate to the 'Favorites' folder at the location below, copy the PRJ file, and paste into the folder with the LAS file.
4. Rename the PRJ to match the LAS file name. For example, if the LAS file is named 'Iowa_2008.las', the projection file must be named "Iowa_2008.prj'.

The 'Favorites' folder is located at the path below:

C:\Users\<user_name>\AppData\Roaming\ESRI\Desktop10.2\ArcMap\Coordinate Systems

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