Lidar manual

Points can also be colored with solid colors, that is, without intensity scaling. This can be useful for distinguishing between points that have been classified as ground vs vegetation by automated or manual devegetation techniques. For example, color 54 14 brown-ish should be entered as -c 0. For example, color 1 the PtArenaGround. Then combine the Ground and Vegetation datasets to see what is considered 'ground' and what is considered 'vegetation'.

In the last example, we used LidarPreprocessor to stitch together two. LidarPreprocessor can combine as many. Similarly, Preprocessor can process and then combine multiple point files e.

For example, to simplify the above classification-based point-coloring exercise into a single command line, do:. When you zoom in, you should see two grains in the data. The most apparent grain, which trends NE-SW at an angle to the screenshot, reflects the orientation of the airborne lidar swaths.

The other grain trends east-west parallel to the top of the screenshot, and is an artifact resulting from LidarViewer's use of floating point numbers. LidarViewer represents data coordinates using floating point numbers, which lack the requisite precision for datasets in UTM coordinates.

Here's what happens: the geographic center of this dataset is around The greater loss of precision of the y northing coordinate results in points being collapsed along east-west oriented lines. Thus you would want to apply an offset as follows: -lasOffset 0.

When you use the -lasOffset command, an 'offset' file is added to the. However, be sure to record the offset you use in case you need to remove it later. LidarIlluminator is an important processing step that allows the point cloud data to be viewed in LidarViewer with a real-time hillshadeing effect, similar to how DEMs are commonly visualized.

How does this work? LidarIlluminator illuminates the point cloud's 'surface' by calculating a normal vector for each point in the dataset. This normal is calculated as the normal to a least-squares approximate best-fit plane through a selection of data points surrounding the point in question.

This selection is chosen either by gathering all the points within a specified radius of the point in question, or by choosing the closest n neighboring points to the point in question. Distances are Euclidean. How wide of a radius to use or how many neighbors to specify depends on the resolution of the dataset, and the best result will come with a bit of trial and error. Too large of a radius or too many neighbors will consider too many points, which has the effect of visually smoothing the topography though the topography is not actually smoothed.

The LidarIlluminator step will add a 'normals' file to the. The approximation radius has to be selected appropriately for a given data set. A good starting guess is to set it to about twice the average point spacing in the data. The value uses the measurement units native to the.

If you specify both -radius and -neighbors, LiDAR Viewer considers only the intersection of the two sets, meaning the up to k nearest neighbors less than radius away.

This is a way of curtailing runaway searches, since otherwise in sparse areas of a data set -neighbors alone might have to go to a very large search radius, which might take a very long time.

See the following section Using LidarViewer on how to use Illuminator and make sure this worked. You can put whatever extension you would like e. For grey-scaled intensity colored point clouds, r, g, and b will have the same value. How to measure the coordinates in LidarViewer will be covered later in this manual, for now though, try exporting the data that lies within a box with coordinates x:[,], y:[,], and z:[0,].

Make z-max high so as not to cut off the tops of any mountains. But we only need columns 0, 1, 2, and 6 x,y,z,intensity. After Exporting, the data looks like this:. Important: LidarExporter reads Offset files created when applying an offset with -lasoffset with LidarPreprocessor. This means that if you export points from an offset dataset, LidarExporter will remove the offset upon export, thus restoring coordinates to their original state.

This tool allows the user to subtract a selected dataset from the. This is useful if one wants to clip data or manually remove vegetation or extraneous points from a LiDAR point cloud. The LidarSubtractor will create another. Illumination must be recalculated for the new.

Show be a power of two; is the recommended number to use. The preprocessor will create a directory of that name and create an index and points file inside that directory. An extension of. Due to floating-point issues, you need a non-zero epsilon to reliably match points between the base file and the selected set.

For airborne LiDAR, a value of 0. For tripod Lidar, you'll want to use a millimeter or even less. Again this value will change with units of original data. Use test2 for this example because it has not been Offset-see footnote below about how LidarSubtractor handles Offset files. LidarSubtractor has probably most commonly been used for subtracting vegetation points from a. Vegetation points can be selected manually in LidarViewer this will be covered later.

However, in this example, we'll subtract the vegetation from the PtArenaAll. The file PtArenaVeg. NOTE : Discrepancies in the point count for input and output files can arise when subtracting points.

This will likely be fixed in later versions, but for now, what this means is that you will not be able to subtract a dataset that has been LidarExported from a. This is because LidarExporter reads Offset files, so exported datasets will have the offset removed. However, because LidarSubtractor does not read Offset files, it does not know to remove the offset from a.

Again, this is only an issue when subtracting datasets that have been produced using LidarExporter. Subtracting points that have been selected from within LidarViewer will work whether or not an offset has been applied to the. The PointSetSimilarity tools compares two selected point sets i. This is useful during a user-study where different users self-classify points i.

For this tool to work you will need 2 selected point sets. The only result from running the program is a similarity value in percent. If you are using.

CalcLasRange is a LidarViewer tool that will read. LidarViewer allows you to make selection of points and fit geometric primitives lines, planes, spheres, cylinders to the selected points.

The parameters of these primitives are printed in the Terminal window when the primitive is created. However if you save the primitive but forget to record its parameters, they can be reprinted using Print PrimitiveFile. Note As of LidarViewer 2. For the above example, the Terminal output when the Primitive was created was:. LidarViewer is designed to work in most visualization environments e. Thus, some of the tools that you find on the menus only work in certain environments.

Similarly, several programs including LidarViewer work on top of Vrui, thus, some of the tools on the menus are not actually specific to LidarViewer, but are rather to Vrui, and may have more obvious functions in other KeckCAVES programs. In the following sections, basic navigation and interaction within LidarViewer is described. LidarViewer's interaction and navigation tools are assigned to buttons on your input device s via the above menus.

In a standard non-tracked desktop or laptop environments the input devices are usually the mouse and keyboard 6-axis mice can be used too. In tracked desktop and immersive environments the input devices are position tracked 'wands', which will have different button configurations depending on brand. This is because such systems do not have tracked controls, meaning that the LidarViewer tools are not independent of the data in 3D space.

In such systems, the controls and tools are locked to the screen plane, thus to interact with the data, the data must either be brought to the screen plane or the controls and tools must be projected from the screen plane to the data.

Its almost always preferable to do the latter. Assigning tools in tracked systems usually involves fewer steps. In tracked environments it is not necessary to project tools to the point cloud because both are independent entities in 3D space, that is, neither are locked in place as the tools are to the screen in non-tracked systems. Thus, assigning tools such as the Measurement Tool or a Locator Tool see below can be done without assigning the Point Cloud Projector just follow the latter three steps described immediately above.

However, assigning navigation tools may be dependent on the type and number of tracked wands in use, and thus this process is likely to be custom to individual visualization environments and will not be covered in this manual. Setting up multiple tools can take several minutes, so to save time at the beginning of LidarViewer sessions, it is useful to save the interaction and navigation configuration that you use most often for certain tasks. To do this,. Navigation in LidarViewer is done though a combination of preassigned and user-assigned controls.

If the center of the crosshairs does not intersect the point cloud, then zoom will be to some location that is wherever the crosshairs center is above, below, outside, or otherwise dissociated from the point cloud, and rotation will be about about that location too, leading to exaggerated rotations.

Panning while maintaining contact between the point cloud and the center of the cross hairs requires assigning a navigation tool, do:. To navigate, simply move the mouse cursor so it is over whichever part of the point cloud you wish to look at, then press the assigned button. The dataset will move so that whichever part was under the mouse cursor now intersects the center of the crosshairs.

Again, just try it. LidarViewer allows you to visualize point clouds with a dynamic hillshading effect, rendering the point cloud so it appears much like a hillshaded DEM see Section 2. Feature recognition and dataset visualization is enhanced by the ability to interactively adjust the lighting or 'sunlight' azimuth and elevation over this 'surface'.

You must preprocess the lidar data with LidarIlluminator to use the hillshading effect-see Section 2. If there is no normals file in the. To turn on the hillshading effect, select Lighting and deselect Use Point Colors. To adjust lighting, select Sunlight Source , and adjust sun azimuth and elevation using the adjacent sliders.

The Show Plane Distance option allows you to visualize the point cloud where points are color coded relative to their distance from a user defined plane in the direction of the plane's normal vector. To do this:. A yellow sphere the Locator will appear. This is what you use to select points. To select points, move the data and place the yellow sphere so that it encompasses points you wish to select, then press the assigned key.

Selected points will be colored green. The Locator size and action selection or deselection can be adjusted from the Interaction Dialog. To open, do:. This can make data selection faster, as when classifying large amounts of vegetation returns. Unfortunately, the locator size cannot be changed once the Locator keys have been assigned. LidarViewer allows you to approximate the orientations of features by fitting geometric primitives planes, lines, spheres, cylinders to selections of points.

This will display Dip and Dip Direction , not strike and dip. The intersection point or line between pairs of primitives can also be determined from within LidarViewer. Then, select primitives by holding the mouse cursor over each primitive and pressing the assigned Dragger key.

Selected primitives will turn blue. Then do:. Use the dialog box to change Measurement Mode. To make measurements, hold the mouse cursor over whichever part of the point cloud you wish to measure, and press the key assigned to the Measurement Tool. To expand the Measurement Dialog box so full measurement precision is shown simply click, hold, and drag the right side of the dialog box.

Several pointer options are available in LidarViewer than can be useful for interactively indicating specific features, however most of these only work in tracked environments. Filed under the Pointer menu is the Clipping Plane tools, which allows you to make parts of a dataset disappear, as when you want to look at something cross section.

This tool does work with non-tracked systems. To use it:. To use, hold the cursor over the dataset and press the key assigned to the Clipping Plane tool. Lighting must be deselected in the Render Dialog. Saving a view point so that a particular look-direction can be exactly restored can be useful for recording the locations of key features, or for making paired figures where the topography in each image should be identically oriented.

This is a simple step. Recording polished 'fly-throughs' and movies demonstrating interactive measurement methods is relatively simple in LidarViewer and all KeckCAVES programs. For instructions see Making Movies need to insert internal link. The reason to do this is deal with a strange format and therefore need to specify which columns to process by using the —csv command which requires a comma delimited. In general this should not be needed due to the all the different input types that the pre-processor allows.

Follow these steps:. Open the. In the above example, there are 9 variables. If I only had 3 variables, the command would look like this:. If you need to stitch numerous files together that are large you may need to specify a folder for the LidarPreprocessor to store temporary octrees.

Generally this will not need to be done as a default folder will be assigned, but if that hard drive runs out of space during processing and you have another hard drive with more free space, this command will help i.

This command is not useful unless you have an external hard drive or multiple internal hard drives. If when processing data, a segmentation fault error message pops up, then you are possibly out of hard drive space, use the following commands. Again, this is likely very rare and does need to specified unless problems occur when pre-processing extremely large files. Please contact your Account Manager for details. There are a series of mounting kits available for the ProLaser 4.

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