EXERCISE 2: GETTING STARTED WITH FUSION

Transcription

1 Exercise Objec ves In this exercise, you ll be using the fully prepared example data to explore the basics of FUSION. Prerequisites Successful comple on of Exercise 1 (Download and Install FUSION and the Example Dataset). Overview of Major Steps 1.Start Fusion and load the Example Lidar Data. 2.Load a Reference Image. 3.Select a Sample to view in LDV. 4.Add a Bare Earth Model. 5.Explore FUSION s Sampling Op ons. 6.Explore FUSION s Display Op ons. Exercise 2 page 1

2 1. Load Example Lidar Data a. Click the shortcut to start Fusion 1. Click the Raw Data bu on on Fusion toolbar to display the Open dialog box. 2. Navigate to your data folder (C:\lidar\SampleData\) and Select the sample dataset (lda_4800k_data.lda) and click Open. This will open the Data Files dialog. The Data Files dialog allows you to change the display Symbology of the lidar data in the Fusion window but, we strongly recommend that you accept the defaults (especially the Symbol set to None) for now. 3. Click OK (read the note below before making any changes). If you change the Symbology by se ng a Symbol other than None and you click the check box next to the Raw data bu on, all of the data points will display in the Fusion window. This may be entertaining and educa onal once but you won t want to do it o en and it is not necessary in order to use FUSION. 4. Save your Fusion project by Clicking the Save icon or File Save As. 5. Name the project exer02.dvz and Save it in a new folder named C:\lidar\Fusion_Projects. 2. Load a Reference Image a. Click the Image bu on 1. Select the sample orthophoto (orthophoto_4800k.jpg) from the sampledata folder and click Open. The image will automa cally display in the Fusion viewer. Fusion requires a reference image before you can view your lidar data in Lidar Data Viewer (LDV). If you don t have a reference image available you can create an intensity image from the raw lidar data to use as your reference image. This capability can be accessed through the FUSION interface: Tools Miscellaneous U li es Create an image using LIDAR point data... If you want to zoom in to any part of the image, Right Click on the loca on you want to zoom to. Zoom out by holding down shi and right clicking the image. You re now ready to view the lidar data in the Lidar Data Viewer (LDV). 3. How to View a Sample in LDV a. To create a sample and view the corresponding Lidar data in 3D: 1. Posi on the cursor over an area of interest in the orthophoto, Le Click and drag a small box (called a stroked box) over the area and release the le mouse bu on this is your sample (see right figure). Note: a small sample works be er (faster) than a large sample. 2. The sample box will be highlighted in the Fusion viewer and LDV, Fusion s 3D viewer, will au Example of lidar data points (top layer) colored by the corresponding reference image (bo om layer) in Lidar Data Viewer (LDV). The stroked box sample selec on is highlighted in the Fusion window... Exercise 2 page 2

3 toma cally appear and load the Lidar data within your sample boundary, similar to the bo om right figure. 3. Use the Basic LDV Naviga on Tips (below) un l you are comfortable with your ability to control the data cloud. Basic LDV Naviga on Tips (Note: LMB = Le Mouse Bu on, RMB = Right Mouse Bu on) LMB + move mouse: Grab and rotate the displayed data (rota on can be up/ down and le /right) It may be easiest to imagine that the data is contained in a glass ball. To rotate the data, use the mouse to roll the ball and thus manipulate the data. LMB + ctrl + move mouse down: Zoom in LMB + ctrl + move mouse up: Zoom out About LDV and Keystroke guide bu on Sample boundary Lidar data shown in LDV. RMB: Ac vate pop up op ons menu for LDV For a complete list of LDV keystrokes, Click the About LDV and Keystroke guide bu on in the bo om le corner of the LDV (highlighted in red in the graphic to Exercise 2 con nues on next page... Exercise 2 page 3

4 4. Add a Bare Earth Model a. Close the LDV and return to FUSION (it will s ll be running & your last sample will be displayed). 1. Click the Bare earth bu on (located on the Fusion toolbar). 2. Select the sample terrain model (4800K_ground_surface.dtm) from the sampledata folder and click Open. 3. Within the Surface model op ons window, you can accept the defaults or define contour intervals and line colors. Once you have chosen intervals and colors or accepted the defaults, click OK. The terrain model will be displayed in the Fusion viewer as a contour map over the orthophoto. 4. Click the Repeat last sample bu on (located on the Fusion toolbar). This will display the same lidar data cloud as before. 5. Right Click within the LDV viewer to access the Right Click Menu. 6. Click on Surfaces (or use the Alt U keyboard op on). The bare earth surface will automa cally display with your lidar data cloud (see top right figure). 7. Access the right click menu again and Click on Data to toggle the data off (or type Alt D). This will allow you to inspect the bare earth surface without the data cloud (see bo om right figure). To turn the data back on use the right click menu and click on Data again or type Alt D again. Once the Bare Earth model is specified in Fusion, it can be toggled in LDV via the right click menu (Surfaces) or typing Alt U. 5. Explore FUSION s Sampling Op ons a. Fusion offers a number of ways to sample and view lidar data. We ll explore several of these op ons in this sec on and you ll use many of the remaining op ons in subsequent exercises. 1. In the FUSION window, Click the Sample op ons bu on to open the Sample Op ons dialog (see Appendix 1). 2. Under the Sample shape sec on, select Stroked circle (the default is Stroked box) and click OK. 3. Select a small stroked circle sample in the Fusion window and view the results in the LDV. 4. Close the LDV. b. Return to the Sample op ons 1. Change the sample shape back to Stroked box. 2. In the Decima on sec on, increase the value to 200 and click OK. The lidar data can be toggled via the rightclick menu (Data) or typing Alt D. 3. In the Fusion window, select a large stroked box sample (sugges on: make the stroked box cover about half the size of the reference Exercise 2 page 4

5 image). It may take a few minutes to extract the sample but the results display very fast in LDV. No ce that the ground is not flat within the sample area as you view the data in the LDV; you ll make it flat in the next sample. Note: See the last page of this document for an 4. Return to the Sample op ons and Select (check) the Subtract ground eleva ons from each return in the Op ons sec on and click OK. appendix describing the Sample Op ons dialog box. 5. Click the Repeat Last Sample bu on. This will repeat the last sample area, but now the data will appear in LDV as flat terrain this is very useful for comparing heights above ground level. 6. Return to the Sample op ons and change the Decima on value back to 1 and deselect the op on to Subtract ground eleva ons. 7. Select the Bare Earth Filter op on to Exclude points close to surface and increase the tolerance to Click OK to close the sample op ons dialog. 9. Select a small stroked box sample in the Fusion window Note that the points close to the ground have been excluded from displaying in LDV. 10. Return to the Sample op ons and select the Include all points op on under Bare Earth Filter. 11. In the Sample op ons window, under the Color op ons, Select Color using image and click OK. 12. Click the Repeat last sample bu on. You should no ce that each lidar return is now painted the color of the corresponding reference image. Keep the LDV open. 6. Explore FUSION s Display Op ons a. To this point, you ve been controlling the display and sample op ons from Fusion s Sample Op ons dialog box. Now, we ll explore a few of the display op ons within LDV FUSION Tip you can only use the Subtract ground eleva ons op on if you ve loaded a Bare Earth Surface (which you ve done). FUSION Tip Some of the sampling and display op ons can be very computer intensive and are appropriate only with a fast computer and a small sample area. You will have to be the judge of what your computer is capable of handling. A class 3 computer is recommended for general lidar data explora on and analysis. FUSION Tip you can only use the Bare Earth filter op ons if you ve loaded a Bare Earth Surface (which you ve done). 1. Access the right click menu and Toggle (either on or off) the Draw all points when moving op on. Click and drag to move the data sample. If you ve toggled the Draw all points op on on, the responsiveness of your display may be sluggish (but it looks good) and if you toggle the op on off, the LDV display will be very responsive (but it won t look as good). 2. Set the Draw all points op on to suit your computer and your preferences. 3. Access the right click menu again and Click the Marker op on. 4. Experiment with the Marker Type and Marker Size op ons however, be aware that some of the marker types only work well with fast computers. If in doubt, keep the marker type set to Points. 5. Back in the Fusion window, Click the Sample Op ons bu on. 6. Enable the Color by Intensity op on. 7. Click OK and then Click Repeat Last Sample. The LDV viewer will display returns according to their intensity value (or the near infrared spectral value). The intensity informa on can be helpful to interpret ground features. However, because the intensity informa on of Exercise 2 page 5

6 the ground features are clustered on only a small por on of the displayed intensity range, the default display parameters make the data difficult to interpret. Let s adjust the intensity display parameters to improve interpreta on. b. Click the Histogram checkbox on the le side of the LDV viewer (see graphic below). 1. The histogram will display (black) along the color legend. 2. You should see that most of the intensity values are clustered in the lower half of the available intensity range. Let s truncate the available range to the approximate range of the intensity values (so that we can interpret the LiDAR data be er). 3. Write down the approximate low and high intensity values that capture most of the histogram (see graphic to le ). 4. Click the Sample Op ons bu on in the Fusion window. 5. Enable Truncate A ribute Range (in the Color sec on). 6. Enter your approximate minimum and maximum histogram values. 7. Click OK and then Click Repeat Last Sample. Now you ve effec vely stretched your intensity data to cover the full color legend for improved interpreta on (see figure below). High intensity values (or high near infrared values) for natural communi es most likely represent photosynthe cally ac ve vegeta on, and in some cases may represent dry bare soil. Lower intensity values likely represent: 1)wet, bare soil, 2) water, or 3) less photosynthe cally ac ve vegeta on To visually interpret the intensity values more effec vely, you will need to truncate your histogram to the values that contain most of your data values. In this example, we will truncate the histogram to a maximum of 30 and a minimum of 1. Truncated histogram and resul ng LiDAR data display in the LDV viewer. Max Intensity Value=30 Default histogram and LiDAR data display in the LDV viewer. Min Intensity Value=1 The figure above illustrates how the data and histogram changes with trunca on. Exercise 2 page 6

7 c. To conclude this exercise, con nue to interact with the data in LDV and FUSION Tip Note: Lidar intensity values are not normalized. The lidar sensor will change its gain or pulse experiment with the following items on the right click menu. Wiggle vision (Alt W) strength during the acquisi on, which changes the return Overhead View (Alt O) intensity of the pulses/returns. The same feature can have Reset Orienta on (Alt R) different intensity values in different flight lines. Hence, the intensity values can be used for interpreta on but it is not advisa Reset Zoom (Alt Z) Image Plate (Alt P) ble to use the values for spectral analysis. d. Turn the truncate func on off and choose the color by op on that seems most appropriate for general visualiza on (color by height is recommended). 1. Save the project: File Save. End of Exercise 2 Exercise 2 page 7

8 APPENDIX 1: SAMPLE OPTIONS The only se ng in the Op ons sec on explored in this exercise is Subtrac ng ground eleva on from each return. This essen ally fla ens the terrain so above ground feature heights can be readily interpreted. Note the other available se ngs under op ons, including the ability to Snap our sample to a POI. Once we have specified a Bare Earth Model and/or a Canopy Surface Model, we can filter (include or exclude) lidar points at a user defined distance from those surfaces. The default Sample shape is a Stroked box, but there are other op ons. Of par cular interest: A Fixed circle is very useful for defining fixed radius plots (when choosing a fixed box or circle, you will have the op on of specifying the size). The fixed circle can be snapped to the plot center by choosing the Snap op on in the Op ons sec on The Decima on op on allows you to reduce the density of the points being sampled. This is especially useful when you select a large sample area. The Returns op on allows you to pick which returns are displayed. This makes analyzing specific returns easier. Enabling this op on can allow you to truncate (or stretch) your histogram so that your data display is more interpretable. The Color op ons (though they re not really sampling op ons) allow you to display the data by a number of a ributes. Usually the most useful op on is Color by height but we will also explore Color using (reference) image and Color by Intensity. Appendix 1 page 8

9 APPENDIX 2: SIMPLE MEASUREMENTS IN LDV 1. Make basic measurements in the LDV a. Start Fusion if needed and Load the project exer02.dvz from the C:\lidar\Fusion_Projects folder. 1. Select a stroked box sample that includes trees. 2. Type, Alt+u to display the bare earth model and Type, Alt+i to display the orthophoto (see right note) on the surface model or access these op ons from the right click menu. You are now able to visualize Lidar points within the measurement cylinder and view the corresponding area of the orthophoto. The order of display is important you cannot display the draped orthophoto if you haven t already displayed the bare earth model. 3. Right click in the LDV window to ac vate the pop up menu and select Measurement marker. This will change the display to an overhead view and show the measurement cylinder. Also, see the Measurement Marker Quick Guide on next page. 4. Move the cylinder by holding down the Shi key and typing with the arrow keys. Move the cylinder so that an individual tree is at its center. 5. Resize the measurement cylinder (Ctrl+Shi +Right mouse bu on + mouse drag up/ down) to isolate the crown of a single tree (see right side graphic). 6. Click and drag the data cloud with the LMB to view the cylinder from the side. 7. Type h to automa cally move the cylinder to the highest lidar point. The value of the measurement marker loca on is displayed in the LDV s window. 8. To measure the ground eleva on of this loca on, type g to automa cally move the cylinder to Lidar points corresponding to the ground surface. 9. You can now calculate this tree s height by simply subtrac ng the ground eleva on from the tree top eleva on. b. Another method to make similar measurements is to automa cally subtract the ground eleva ons, let s do that now 1. Type Alt+i to turn the display of the orthophoto off. 2. Likewise, Type Alt+u to turn the display of the bare earth model off (or turn these op ons off from the right click menu). The Measurement Cylinder 3. Return to the Fusion window and click the Sample Op ons bu on. 4. Enable the Subtract ground eleva ons from each return op on and click OK. 5. Click the Repeat last sample bu on. No ce that the sample area is flat in LDV and the eleva on bar to the le is providing height above ground. 6. Right click in the LDV window to ac vate the pop up menu and select Image plate (Alt p) to turn the orthophoto on below the lidar data (you may have to zoom out to see the image plate if you are zoomed in). 7. Right click in the LDV window to ac vate the pop up menu and select Measurement marker. 8. Move and resize the cylinder as you did before to highlight a single tree. 9. Click and drag the data cloud with the LMB to view the cylinder from the side. Now, when you type h, the measurement marker moves to the tree top and gives you the height of the tree (there is no need to type g in fact, that func on is inac ve). If the height numbers are black and are hard to see with the background, use the Appendix 2 page 9

10 APPENDIX 2: SIMPLE MEASUREMENTS IN LDV right click menu and click the Color op on and change the Axis color to a contras ng color (white works well). c. If you wish to take mul ple measurements, you can record them to a CSV file (readable in Excel) by following these steps: 1. Move the measurement cylinder around using Shi + arrow keys and navigate to another tree. 2. Resize the cylinder to properly isolate a tree within the measurement cylinder. At the next tree, measure the tree top (type h and then Enter). 3. If you have disabled the Subtract ground eleva ons op on then you should also measure the ground surface (type g and then Enter) otherwise there is no need to measure the ground surface. 4. Repeat this for two three more trees. 5. Now right click to ac vate the LDV popup menu and select Save measurement line. This will allow you to save the measurements you recorded in a XYZ comma separated (.csv) file. 6. Navigate to C:\lidar\SampleData and name your file treeheights.csv and click Save. 7. Launch Excel and open treeheights.csv to view the measurements you recorded. Measurement Marker Quick Guide Shi + Arrow keys: moves the cylinder. Ctrl + Shi + RMB drag up: increases cylinder size. Ctrl + Shi + RMB drag down: decreases cylinder size. h: moves the measurement marker to the top return in the cylinder. g: move the measurement marker to the lowest return in the cylinder (disabled if Subtrac ng ground eleva ons automa cally). Enter: records (in memory) the current X,Y,Z of the measurement marker. Appendix 2 page 10