The Live View Returns Tab

*Live View is available in all license levels of LP360.

Return combinations are selected on the Returns tab of the Live View dialog seen below.

Note that, just like the Classification tab, the Returns filter can be separately applied to the Points and TIN channel.

LAS versions 1.0 through 1.3 support 5 returns if the data are ASPRS LAS compliant. However, these versions of LAS reserved 3 bits for return information and hence can support up to 7 returns (the value 0 is reserved for other uses). Some software applications support using the non-standard return 6 and 7 in these lower LAS formats (note that return number must be deduced by sensor hardware or post-processing software that has knowledge of the sensor returns). Due to the prevalence of the non-standard use of returns 6 and 7, we elected to allow this in the Live View filter. Thus the Returns tab shows 7 returns for LAS 1.0 through LAS 1.3.

LAS 1.4 supports up to 15 returns. If the current Active LAS Layer contains 1.4 format data, the Returns tab will show 15 returns.

Overview of the Live View Returns Tab

Setting/Clearing Returns

The returns are turned off and on by simply pressing the associated button in the Returns tab. Rows represent pulses with a certain number of returns (e.g. the third row represents outgoing pulses for which three returns were detected). Columns represent the particular return number. Just like the Classification tab, a tool tip will list the return if you hover the mouse pointer over a return button.

You can set/clear an entire row or column by pressing the button at the side of the row or bottom of a column.

Quick Settings

Several Quick settings are available using tools in the upper right of the Returns tab. A drop-down list allows you to select common combinations of returns (e.g. Last Returns, First Returns, etc.). Similar to the Classification tab, there tools to select all returns or to clear all returns.

If you manually set a named return set by pressing return buttons in the dialog, the name will appear in the drop-down list. For example, if you enable only the right-most return of every row, you have selected Last Returns. The drop down selector will change to read “Last Returns.”

Unknown Returns

Unfortunately, LAS supports the value zero for both the number of returns and the return number. This gives rise to a large collection of non-standard return encodings. For example, Return 0 of 4, Return 0 of 0, Return 3 of 0 and so forth. It is disappointingly common for these combinations to appear for some points in a LIDAR data set. The encoding of Return 0 of 0 is very typical of point data derived from dense image matching (such as sUAS point clouds).

It is also not uncommon to find incorrectly numbered standard returns. For example, a return labeled “3 of 1” is clearly an error.

You can enable and disable display for erroneously recorded returns using the Unknown button at the lower left of the Returns tab. In fact, this can make a nice QC tool for finding incorrectly labeled returns.

Return Symbology

Right Clicking a Return button will invoke the return dialog. From this dialog, you can chose to operate on the selected class/return, all On Classes/Returns or all Off Classes/Returns.

Selecting one of the three options brings up a menu.

Selecting Symbology brings up the dialog for choosing point color and size. Selecting Assign Random Color will assign a random color to the selected returns

Color Grouping

Note that using the right click function for multiple Classes/Returns can be very handy for color grouping. For example, to color all last returns red, select Last Returns in the drop down list on the Returns tab. Now right click on one of the return buttons and select All On Returns. Navigate to Symbology and set the color to Red. Now all last returns will display in red.

Trouble Shooting Returns

If you are not seeing what you expect when setting returns, be sure to consider the following:

• Recall that, like Classification, Live View supports separate Point and TIN channels. Thus you might have a combination such as All Returns for the point channel and No Returns for the TIN channel. If a view display mode is set to TIN, you will not see anything in that window.
• Returns are often not correctly encoded in LAS. For example, 0, 6 and 7 are never supposed to be used in a LAS 1.0 to 1.3 compliant file whereas the value 0 should never be used in a LAS 1.4 file. If points encoded with these values and you do not have the Unknown button enabled, these points will not display.
• There may be so few points of a particular return combination that you simply are not seeing them in the display.  For example, return 5 of 5 would typically represent a low fraction of the total points. Due to the way LP360 creates fast display pyramids, these points may not be represented at all in the zoomed-out views.