Creating Blocks Within TerraScan
Terrascan organizes LiDAR data into blocks to reduce memory usage and processing times. These blocks can also be processed and edited individually.
Blocks can be overlapping or non-overlapping.
If you make the blocks non-overlapping you may run into future issues with connectivity of the blocks (i.e if you are trying to interpret contours they may end before the edge of the block because it doesn’t have continuing information to create them.
Import the LiDAR points using the project dialogue
Click ok and the following dialogue will appear. You want to select “create grid blocks”, “no overlap” and “use from file” as shown to the right.
This creates a grid of boundary blocks but they will not immediately be loaded onto your screen.
Change the text style so that generated block text is visible.
To draw the blocks created a few steps above in your viewer, go to the draw block boundaries dialogue box.
Locating your block from the project window
Note – must have mouse hovered over window to see the selected block
Identifying your block from the viewer
Select the block you would like to identify using the mouse
Now that we have blocks we can load the information in each block individually to decrease processing time.
In the TerraScan menu select File –> Open block
Nothing happens until you select a block in your viewer. Once selected the LiDAR points will appear
You can adjust the display settings using the Terrascan –> View –> Display Mode
Once the display mode is open you can see that “Color by” has a variety of default options for displaying your data.
View – Choose what view to apply changes to
Color by – change colour of points
Colors – Coloring scheme allows to specify range of colours
Speed – Allows to display more points quickly (Normal is typical)
List of classes – (default ground) allows you to toggle on/off classes of points
Fit – quickly change extent of the view to fit extent of loaded block.
The next step can be tricky so we will start with discussing the basics. When you create a TerraScan project the viewer polygons are NOT intrinsically linked with the block boundaries drawn in your viewer. Sometimes outlier points caused by error or calibration can create blocks in areas outside of the study area. To get rid of these we can delete unnecessary blocks in the viewer and recreate the study area based on the new block boundaries. I will discuss this using pictures.
When you create your project blocks based on your point data, often you have points outside of your area of interest.
Delete the blocks that you are not interested in (i.e outside red study area)
When you complete the above step the blocks are not deleted from your project, just from your viewer. To fix this and relabel your blocks you must recreate your project. Select the points in your project dialogue and select ‘delete definition’. Go to your “blocks” folder (location that you saved your project blocks to) and delete them all
Your project content is now gone. We must recreate it based on the remaining block polygons in your viewer.
Select the remaining blocks in your viewer
These are no longer a part of your project. You need to draw them into your project using the ‘add by boundaries’ option. Make sure you do these two functions on different layers or you will have two of each outline in one layer. After this is done you have new blocks but they are not drawn.
The next step is to draw the boundaries on your new blocks which are defined from a selection of the blocks created in your original project
The final step is to import your .las files. The difference between this and the first time is that this time you have to select “Ignore outsideBlocks”
To check that it worked view the points in a block
Don’t forget to save your project
How to Query LiDAR Points
In the Terrscan window each LiDAR point is listed
The “show location” and “identify” tool buttons should look familiar. These are used exactly the same as they are in the project menu for blocks.