LAS Dataset Training and the LAS Dataset Toolbar

in this presentation you'll learn about working with last datasets or la s datasets in ArcGIS version 10.1 this is a brief introduction to lidar data in general a plane flies over the landscape and shines a laser beam down at the ground the beam reflects back to the plane as pulses this returned information is corrected for positional errors and recorded as XYZ data in addition the intensity of the signal in the time it was captured are collected as additional attributes the X Y Z coordinates are depicted as the green dots in this image these are lidar data for downtown Providence Rhode Island these data were collected between fall of 2010 in winter of 2011 for this presentation we will be working with the subset of these data at Roger Williams national memorial here we can see the tops of buildings some data are collected for the outer walls of the buildings as well and we can see trees and other vegetation this ellipse shows the location of Roger Williams National Memorial this is where we will need to acquire the data we will be working with these are the four last files for this area I downloaded these files to my computer from the Rhode Island geographic information system website these will be my input files for the last data set I will be creating what is the last data set a last data set is an ArcGIS file format that acts as a pointer to source last files the file extension for the last data set is dot LASD or last D last D files are very small in size and need to accompany the last files to function if the source last files are removed then the last data set won't display in ArcGIS I will be using the tool create last data set this tool form requires that I enter any input files I wish to use in the name of the output last data set I can also choose to compute statistics and store the relative path to my files using the checkboxes at the bottom of the tool form the other options are important for the work we will be doing today as I won't be using any constraints to the surface I am creating the orange circles on the screen show the areas where I need to click to set the input and output parameters I will need you can enter these pieces of information in any order before clicking the ok button here is the tools completed form just before I push the OK button we can see the list of my 4 input files we can also see the name of my output last data set that I am creating this file has an extension of last D we can also see the coordinate system of my last data set I suggest setting this in the event this information is an explicitly set in the input last files I would consult the metadata of the last files for the coordinate system parameters needed the last option is to store relative paths I check this option in the event I wish to give the last data set to someone else or if I wish to copy it to a DVD before working within exploring last data sets in arcmap you will want to turn on the last data set toolbar this can be done by clicking on the customize menu selecting the toolbars option and checking off the last data set toolbar by clicking on the checkbox to the left of the label this is depicted by the green ellipse you will then be allowed to dock this toolbar with the other ArcGIS toolbars at the top of the screen for this presentation I have docked mine just above the table of contents on the left side of my screen as indicated by the orange arrow the last data set toolbar offers a lot of functionality for quickly viewing your lidar data within arcmap you can quickly display all your data or display it based on ground or non ground returns or even first returns as an example this can be useful for distinguishing between vegetated and non vegetated areas using the last data set toolbar within arcmap if you click on the word filters or the drop down icon represented as an inverted triangle the list of choices will appear from this list you can see the four options available the next series of slides will depict how our data appear in arcmap when using these various options when we select the option all we can see all of our lidar data notice that our map legend represents how the default colors relate to the various elevation values here we can see the lower elevations as various shades of blue and green and the higher elevations as Browns and grey notice the building rooftops in shades of brown here we can see our filter that displays non ground return values from our last data set this looks similar to the filter we use for all values here we can see our filter for first return values this looks similar to the filter we use for all values as well these are pulses of light that are returned to the plane first in contrast apostles of light that take longer to return to the plane an example of light that would return first to the plane is pulses of light from the top of buildings or the bare ground this map represents the values in our lidar data set that have been classified as bare earth or ground values using this filter we can remove the elevations that represent vegetation or buildings only elevation values that are believed to be from the ground surface such as roads or even the surface of land or water bodies are represented here these filter types are important because they can determine what values get converted using the last data set to raster conversion for example one way to create a raster GIS data set that only includes ground or bare earth values is to use the ground option from the last data set toolbar filter just as we discussed in the previous slide even though the input of the command is the last data set it only processes the results of the applied filter this is unique behavior in arcmap because rarely does the setting in arcmap dictate the output of a geoprocessing tool the next set of slides we'll go through using the last data set to raster conversion this is a geoprocessing tool form for the last data set to raster conversion the input of this is the last data set the output is a raster surface that can be used for further analysis in arcgis or as a layer in your maps for this example we will use the default interpolation methods you have control over the type of interpolation if you so choose for example you can use triangulation interpolation methods or the default process that uses binning of cell values data binning is a data processing technique used to reduce the effects of minor lidar data errors the original data values which fall in a given small interval AB in are replaced by a value representative of that interval the default binning option for cell assignment is average however there are choices for inverse distance weighted IDW maximum minimum or nearest here we can see the input last data set is named last data set Roger Williams National Park the output raster data set that we will be creating is named ground last data set Roger Williams National Park the extension is IMG and this is important because it dictates to arcgis the file format of our output raster data set i enjoy working with our dass imagine image files and that is why I selected IMG as a file extension you have other choices here and some people choose to use TIFF files for example the extension for TIFF files is dot gif you may choose to use the default values or you may wish to read the help for further information regarding this command I am going to use the remaining default values and then press the ok button this is the output of the last data set to raster command you may not find this very interesting to look at because it is just shaded elevation values using shades of black in dark gray one option you have is to change the default shading to stretch between other colors in this situation I like to create a real shade of my raster surface this will allow us to better enhance the values to emphasize the 3d nature of the source data we will now look at the hill shade tool this tool is found with your ArcGIS geoprocessing tools we will then show you the same area shaded in shades of black to gray but represented as the hill shaded surface I think you will agree that the hill shaded representation of this surface will be more interesting to look at this is the geoprocessing tool form for the hillshade command this requires that we enter the input raster data set name in our case the raster we created that represents ground returns from our lidar data the output is a hill shade of a raster surface in this example I named the input raster using the same name I gave the ground raster surface created in the previous steps you can click on the Browse button represented by the orange circle to add this data set as the input raster for the output raster I use the same name but prefaced it with the word Hill shade you are free to use your own naming convention for the remaining optional values I like to use the defaults but you can experiment around with the azimuth and altitude values to change the Sun angles to represent your season and time of day I select a Z value of one and then push the OK button this is the output Hill shade raster surface I think you will agree that this is more aesthetically pleasing here you can see roads the railroad corridor the residential areas where there are buildings in the general lay of the land surrounding Roger Williams National Park in downtown Providence Rhode Island we are now going to see a more advanced technique for creating a raster surface from our lidar data we already did this using the ground filter on the last data set toolbar but we now want to do it independent of arcmap why would we want to do this well one reason this approach is useful if you want to create a raster surface from a last data set using model builder we are now going to work with the classification button on the last data set toolbar this button activates a drop-down list of choices we are interested in knowing the code values for a lidar data so we will select the class option we will use these code values to determine which of our lidar points have been classified as ground we will use this value for ground as input into the next tool we will be using by symbolizing our last data set by class we can see how our lidar data are coded we are interested in ground returns so we can see that ground return values are coded with the value of 2 please remember this value if you choose to create a raster surface of classified ground returns we aren't actually going to use this approach here but it is good to note this option in the event you are creating the ground raster surface using model builder the input would be your last data set the output would be the name of the output layer you are creating to extract just the ground values select the value of 2 for the class code you can then use this output layer as the input layer of the tool last data set to raster you are free to explore using the make last dataset layer if you wish to but since we already created our raster surface using the previous approach we are going to move on and look at additional functionality of the last dataset toolbar going back to the last dataset toolbar besides changing the filter on our data or symbolizing the data based on classification or elevation we can also choose how our lidar data are represented in arcmap we can display these data as elevations by aspect by slope or using contour lines those of you familiar with tins or Terrain data models you may see a similarity these data are symbolized using triangles the three corners of the triangle are connected to three neighboring elevation points to create a complete surface let's take a look here we can see our lidar data symbolized by elevation using tin faces or little triangles look closely and you can see little triangles on the screen here we can see our lidar data symbolized by aspect using these tin faces again we can see some of the triangles triangles colored red have a northern aspect triangles in dark blue have a Western facing aspect scientists use aspect when they are conducting vegetation research as some species grow best when they live in an environment that has a suitable aspect similarly here we can see our lidar data symbolized by sloped areas in red have very steep slopes and areas in green have little or no slope to them an additional way to symbolize our data using the last dataset toolbar is by selecting the contour option here we can see contour lines of our lidar data being automatically generated if you need better rendered contour lines then I suggest working with the geoprocessing tools for creating contours people familiar with ArcGIS may have viewed 3d data using the spatial analyst viewer or the arc globe viewer however there is a new 3d viewer that is included with the last dataset toolbar this tool is the last icon on the far right of the toolbar and I have circled it here in green be sure to view your last dataset using this 3d viewer to fully explore lidar data finally there's a very powerful profile tool with the last dataset toolbar it is circled here in green in the upper right corner of the screen the profile tool allows you to view a profile of a rectangular swath of your data here we can see a profile of the data for this Providence area with this profile tool you're able to zoom in to the profile or select individual points within the profile this tool is very robust because you can also edit your last data sets and have the results written back to your source last data files editing classification values in last files won't be covered in this tutorial here we can see the park area represented by the orange park boundary I'm going to turn on the last data set and then I'm going to use the profile tool again the park boundary in orange now I'm going to click on the profile tool and now I get this crosshair on the screen and if I click release it starts to draw a line then I click again release and now my line is completed now I'm able to go to the right or left and a rectangle will appear I'm trying to match you can only have it go so wide there is a limit if I go too far I see this do not continue icon up here so I'll have it generally match the park area click the button to finish that rectangle and now I can see in my profile tool the various elevations based on the legend in arcmap this concludes our presentation please e-mail roland at EDC uri edu if you have further questions

Channel: Roland Duhaime

Views: 16,792

Rating: 4.9411764 out of 5

Keywords: LiDAR, LAS, ArgGIS, LAS Dataset, LAS Dataset Toolbar, Training (Industry), 3D

Id: G8IC6dD5L-A

Length: 21min 17sec (1277 seconds)

Published: Mon Sep 23 2013