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Sample Point Generator (SPGen): Users Manual

Learn how to use the Sample Point Generator (SPGen) ArcView application to quickly create sample points for data or field sampling in any area of interest. Choose from five categories and two sampling routines to generate random or systematic sample points.

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Sample Point Generator (SPGen): Users Manual

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  1. S A M P L E P O I N T G E N E R A T O R An ArcView 3.2+ Application Acknowledgements Forest Health Technology Enterprise Team would like to acknowledge both the San Dimas Technology and Development Center and Colorado State University and for their support in this effort. We would also like to thank the Inventory and Monitoring Technology Development (IMTD) Steering Committee for partial funding of this User’s Guide. Sample Point Generator (SPGen): Users Manual

  2. S A M P L E P O I N T G E N E R A T O R An ArcView 3.2+ Application Authors Vern Thomas, FHTET Marla Downing, FHTET Robin Reich, Colorado State University Sample Point Generator (SPGen): Users Manual

  3. S A M P L E P O I N T G E N E R A T O R An ArcView 3.2+ Application Random Point Generator Options The Sample Points Generator (SPGen) ArcView application allows the user to quickly create sample points within any area of interest for data or field sampling. There are five basic categories from which to create sample points.  SAMPLE POINTS WITHIN THEME EXTENT  SAMPLE POINTS WITHIN SELECTED POLY(S)  EQUAL NUMBER SAMPLE POINTS IN POLY’S  AREA WEIGHTED PROBABILITY SAMPLE POINTS  SYSTEMATIC SAMPLE POINTS Four of the five categories have two sampling routines: 1) Basic and 2) Minimum Distance (Systematic Sample Points () does not have minimum distance). CLASSIC – Sample points created are truly random with no minimum distance constraint. MINIMUM DISTANCE – Theses functions have a user-entered minimum distance between sample points. The greater the distance, the more regular/systematic the sample point pattern becomes. This is useful when the user needs a more even sampling across the area of interest.      Sample Point Generator (SPGen): Users Manual Page 1

  4. SAMPLE Point Generator  1A  Random Points Within Theme Extent: CLASSIC Definition Random points are generated across the theme extent where the points fall within polygon features. Themes with many polygons may have some of those polygons with no sample points and others that contain many. This option is useful when the user has a theme containing two or more polygons and wants to create true random points throughout the theme area regardless of how many points may or may not fall within each polygon.   Random points are generated within the theme’s overall extent only where they fall within any theme polygon feature. From the MALE SAMPLE POINTS pull-down, select 1A Random Sample Points: BASIC.  The Select POLYGON Theme popup window appears. Select the polygon theme in which you want to create sample points and single-click the OK button.  Next, select the sample point theme from Select Sample Point Theme popup window and single-click the OK button. continue   NOTE: You can use this function with single polygon themes (e.g., forest boundary). Sample Point Generator (SPGen): Users Manual Page 2

  5. SAMPLE Point Generator 1A  Random Points Within Theme Extent: CLASSIC continued from page 2   The Enter The Number of Sample Points To Create popup window appears. Enter the desired number of sample points and single- click the OK button. At this point, the system will begin creating the random sample points.  Typical results of using the Random Sample Points in Theme Extent: BASIC function. Notice that the distribution of sample points includes some large open areas with no points, and other areas where the points are more clustered: this is typical of a random point pattern.  Sample Point Generator (SPGen): Users Manual Page 3

  6. SAMPLE Point Generator 1B  Random Points Within Theme Extent: MIN DISTANCE Definition Random points are generated within theme extent and and as long as the points intersect any polygon feature within the theme. Points are located no closer than the user-entered minimum distance between sample points. This option is useful when the user has a theme containing two or more polygons and wants to create random points that have a minimum distance from each other throughout the theme area regardless of how many points may or may not fall within each polygon.   From the MAKE SAMPLE POINTS pull-down menu, select the 1B Random Sample Points: MIN DISTANCE option.  The Select POLYGON Theme popup window appears. Select the polygon theme to receive sample points and single-click the OK button. continue   Sample Point Generator (SPGen): Users Manual Page 4

  7. SAMPLE Point Generator 1B  Random Points Within Theme Extent: MIN DISTANCE Continued from page 4  The Select Sample Point Theme popup window appears. Select the sample point theme and single-click the OK button.  The Enter Minimum Distance popup window appears. Enter a minimum distance between sample points and single- click the OK button. In this example, the minimum distance is set at 1609 meters (1 mile). Notice that the system estimates and suggests the greatest value that the minimum distance should be set. In this example, any value less than 2749 meters should work without loosing sample points due to too many sample point for a particular area based on the minimum distance entered. The Enter The Number of Sample Points To Create popup window appears. Enter the desired number of sample points and single- click the OK button. NOTE: It is important to know your data’s projection so you will know the correct units to enter for minimum distance. (continue )   Sample Point Generator (SPGen): Users Manual Page 5

  8. SAMPLE Point Generator 1B  Random Points Within Theme Extent: MIN DISTANCE Continued from page 5   At the Enter the Number of Sample Points to Create input window, enter the desired number of sample points to create. Notice that the input window indicates a maximum number of sample points to enter. In this example, the system estimates that the maximum number of sample points is 218. This number is based on the entered minimum distance enter in the previous step and should be used as a guide only. In our example, we entered 100 sample points (well under the estimates maximum).  Typical results of using the 1B  Random Sample Points: MIN DISTANCE function. Notice that the pattern of the sample points includes some large open areas with no points, but no areas of closely clustered points due to the limits of the minimum distance between points (compare these results to the CLASSIC model results).  Sample Point Generator (SPGen): Users Manual Page 6

  9. SAMPLE Point Generator 2A Points Within Selected Polygon(s): CLASSIC Definition True random points are generated within a selected polygon or set of polygons within a theme. This option is useful when the user has a theme containing two or more polygons of interest and wants to create true random points within specific polygonal areas (e.g., stands) for a field crew to visit or statistical sampling.   The user selects the polygon or polygons to receive random sample points. Use the ArcView Feature Selection tool to select the polygon(s).  From the Random Points pull-down menu, select the 2A  Random Sample Points: CLASSIC option. continue   Sample Point Generator (SPGen): Users Manual Page 7

  10. SAMPLE Point Generator 2A Points Within Selected Polygon(s): CLASSIC continued from page 7  The Select Polygon Theme popup window appears. Select the theme containing the selected polygon(s) to receive random sample points. Single-click the OK button to continue.  Next, from the Select Sample Point Theme popup window, select the sample point theme and single-click the OK button to continue.  Enter the total number of sample points to be placed within the selected polygons and single-click the OK button. In this example, the user entered 20 sample points. The system then begins to create the random sample points. See the next page for the results of the random point generation (). continue     Sample Point Generator (SPGen): Users Manual Page 8

  11. SAMPLE Point Generator 2A Points Within Selected Polygon(s): CLASSIC continued from page 8  The results of the random sample points within the selected polygons. Notice that the sample points fall only within the selected polygon feature(s) of the theme. Also notice that the pattern of the sample points includes some large open areas with no points, and other areas where the points are more clustered. This is typical of a random point pattern.  Sample Point Generator (SPGen): Users Manual Page 9

  12. SAMPLE Point Generator 2B Points Within Selected Polygon(s): MIN DISTANCE Definition Random points are generated within selected polygon(s) only and points are located no closer than the user entered minimum distance between sample points. This option is useful when the user has a theme containing multiple polygons and wants to create evenly distributed sample points within a polygon area for a field crew to visit.   User selects the polygon or polygons to place random sample points within. Use the ArcView Feature Selection tool to select the polygon(s)  From the Random Points pull-down menu, select the 2B  Random Sample Points: MIN DISTANCE option. continue   Sample Point Generator (SPGen): Users Manual Page 10

  13. SAMPLE Point Generator 2B Points Within Selected Polygon(s): MIN DISTANCE continued from page 10   From the Select Polygon Theme popup window, select the theme containing the selected polygon(s). Single-click the OK button to continue.  Next, from the Select Sample Point Theme popup window, select the sample point theme, and single-click the OK button to continue.  Enter the minimum distance between sample points. In this example, the user entered 1000 meters and single-click the OK button. NOTE: SPGen gives the user some guidance in regard to an appropriate minimum distance. In the example, SPGen calculated an estimated minimum distance less than 1423 meters given the area of the selected polygons. Use this as a guide, not an absolute value. It is best to experiment with different minimum distances. continue   Estimated Minimum Distance  Sample Point Generator (SPGen): Users Manual Page 11

  14. SAMPLE Point Generator 2B Points Within Selected Polygon(s): MIN DISTANCE continued from page 11   Enter the number of sample points to create within the selected polygons. NOTE: SPGen calculates the maximum Number of sample points that can be created given the area of the selected polygons and the minimum distance entered in the previous step. In the example to the right, SPGen has estimated that the user may enter a maximum of 28 sample points. In this case we entered 20 sample points. Single click the OK button to continue. NOTE: It is important to know your data’s projection so you will know the correct units to enter for minimum distance.  The results of the random sample points within the selected polygons. Notice that the sample points fall only within the polygon feature(s) of the theme. Also notice that the pattern of the sample points is more evenly distributed with no areas of closely clustered points due to the limits of the minimum distance between points.  Sample Point Generator (SPGen): Users Manual Page 12

  15. SAMPLE Point Generator 3A Equal Number Random Points in Polygons: CLASSIC Definition The system creates a user-defined number of random points generated within each polygon of a theme (e.g., 6 points per polygon). This option is useful when, for instance, the user has a stand polygon theme containing multiple polygons and needs to have the same number of sample points in each stand regardless of stand area.    From the Random Pointspull-down menu, select the 3A  Random Sample Points: BASIC option.  From the Select POLYGON Theme popup window, select the polygon theme to receive random sample points. Single-click the OK button to continue.  From the Select Sample Point Theme popup window, select the sample point theme and single-click the OK button. Something in continue   NOTE: This function will create sample points in every polygon in the theme unless there is a selected set of polygons. If there is, it will create sample points only in the selected polygons. Sample Point Generator (SPGen): Users Manual Page 13

  16. SAMPLE Point Generator 3A  Equal Number Random Points in Polygons: CLASSIC continued from page 13  In the Enter the Number of Sample Points popup window, enter the number of points to be placed in the largest polygon area. In this example, the user entered “5” as the number of random points to be placed in each of the theme’s polygons.  Typical random sample points results using the 3A  Equal Number Random Points in Polygons: CLASSIC function. NOTE: The points will look clustered in smaller polygons and generally more widely spaced in larger polygons.  Sample Point Generator (SPGen): Users Manual Page 14

  17. SAMPLE Point Generator 3B  Equal Number of Random Points in Polygons: MINIMUM DISTANCE Definition The system creates a user-defined number of random points generated within each polygon of a theme (e.g., 6 points per polygon). Random points are generated within each polygon and are located no closer than the user-entered minimum distance. This option is useful when, for instance, the user has a stand polygon theme containing multiple polygons and needs to have the same number of sample points in each stand with a minimum distance between points. NOTE: Smaller polygons may not get the full complement of sample points!!!    From the Random Points pull-downmenu, select the 3B  Random Sample Points: Minimum Distance option.  From the Select Polygon Theme pop-up window, select the polygon theme to receive sample points.  From the Select Sample Point Theme pop-up window, select the sample point theme. continue   Sample Point Generator (SPGen): Users Manual Page 15

  18. SAMPLE Point Generator NOTE: It is important to know your data’s projection so you will know the correct units to enter for minimum distance.  3B  Equal Number of Random Points in Polygons: MINIMUM DISTANCE continued from page 15   Enter the number of random points to be placed in each polygon and click OK. In this case, we want 5 sample points per polygon regardless of polygon area.  Enter the minimum distance between sample points in meters. In this example, the user entered 800 meters (~1/2 mile). Notice that SPGen estimates the the largest minimum distance based on the smallest polygon in the theme. In this case, however, the user desires 800 meter minimum distance.  A report box may appear if some polygons did not receive the allotted number of points. This may occur if a polygon has too small an area to accommodate the number of sample points with the minimum distance. You can choose to keep the points or reduce the minimum distance or reduce the number of points (or both) and rerun.  Typical results of 3B  Equal Number of Random Points in Polys: MIN DISTANCE.   Sample Point Generator (SPGen): Users Manual Page 16

  19. SAMPLE Point Generator 4A  Area Weighted Probability Random Points: CLASSIC Definition The user first enters a total number of random points to be created and the points are then distributed within the polygons where the larger the polygon area, the more probability that that a random sample point will be placed within the polygon. Example: You would use this design when the variable of interest is correlated to size of the polygon such as forest surveys where the larger stands will contribute more to the overall mean than the smaller stands. If the variable of interest is Not correlated to to polygon size, then the variance may be larger than if you did a simple random sample.   From the Random Pointspull-down menu, select the 4A  Random Sample Points: CLASSIC option. From the Select Polygon Theme popup window, select the theme containing the selected polygon(s) to receive random sample points. Single-click the OK button to continue. continue  NOTE!!! The system will quickly calculate area and probability ranges. This make take a few seconds to a few minutes depending on the size of the theme.  Sample Point Generator (SPGen): Users Manual Page 17

  20. SAMPLE Point Generator  4A  Area Weighted Probability Sample Points: CLASSIC continued from page 17 NOTE: The system calculates area ranges and probabilities before continuing onto step 3.  From the Select Sample Point Theme popup window, select the sample point theme and single-click the OK button.  Enter the total number of sample points to create within the theme and single-click the OK button. The system will then begin to create sample points.  Results of the Area Weighted Probability random sample point process. Notice that the pattern of the sample points is random and that some of the smaller polygons contain no sample points while the larger polygons contain more points.   Sample Point Generator (SPGen): Users Manual Page 18

  21. SAMPLE Point Generator 4B  Area Weighted Probability: MINIMUM DISTANCE Definition Random points are generated within the theme polygons. The probability that a polygon will receive a random sample point increases with the size (area) of the polygon. The user enters a total number of points to create and the points are then distributed within the polygons where the larger the polygon, the more probability that that polygon will have a random sample point placed within itself. Random points are generated within each polygon and are located no closer than the user entered minimum distance between sample points. This is useful when the user is doing a spatial statistical analysis of the landscape. The user may need a specified number of random sample points with a more regular pattern and which have a representative distribution by area from the different cover type polygons.   From the Random Pointspull-down menu, select the 4B  Random Sample Points: MIN DIST option. continue  Sample Point Generator (SPGen): Users Manual Page 19

  22. SAMPLE Point Generator 4B  Area Weighted Probability: MINIMUM DISTANCE continued from page 19  From the Select Polygon Theme popup window, select the theme containing the selected polygon(s) to receive random points. Single-click the OK button to continue.  From the Select Sample Point Theme popup window, select the sample point theme and single-click the OK button.  Enter the total number of sample points to create within the theme and single-click the OK button. Enter the minimum distance between sample points in meters. In this example, the user entered 1609 meters (1 mile). SPGen will then begin to create sample points. Notice the system estimates the largest minimum distance to use given the area of the theme. In this example, it suggests that the user may use a minimum distance of 2749 meters or less. continue     Sample Point Generator (SPGen): Users Manual Page 20

  23. SAMPLE Point Generator 4B  Area Weighted Probability: MINIMUM DISTANCE continued from page 20  Typical results of the Area Weighted Probability: Min Distance random point function. Notice that the pattern of the sample points appears fairly regular, though it does include some open areas with no points, but no areas of closely clustered points due to the limits of the minimum distance between points NOTE: If the minimum distance is too great given the number of sample points entered, SPGen will attempt to create as many sample points as possible. When it cannot solve for anymore points it will pop-up a warning message informing the user that it cannot populate all requested sample points and that the user should either reduce the minimum distance or the number of sample points.  Sample Point Generator (SPGen): Users Manual Page 21

  24. SAMPLE Point Generator 5  Make Systematic Grid Cell Polygons Definition A polygon can be populated with sample points within a system of grid cells to support homogenous sampling across the polygon. Placement of points within the cells can be random or aligned. Before these points can be assigned, however, the user must select the polygon and define the grid pattern for it. Use this design when there is a gradient in the population being sampled. If the variable of interest is randomly distributed, there will be no difference between this method and a simple random sample. Systematic sampling may also cost less by minimizing travel time.   Select the polygon(s) that you want to place systematic sample points within. You do not have to select any polygons if you want the entire theme to be covered by the systematic grid.  From the Random Points pull-down menu, section, select the 5  Make Systematic Cell Polygons option. continue   Sample Point Generator (SPGen): Users Manual Page 22

  25. SAMPLE Point Generator 5  Make Systematic Grid Cell Polygons continued from page 22  From the Select Systematic Cell Theme popup window, select the systematic cell theme (this shape file comes as part of your ZIP file). If you don’t have this file in the view, then load it before continuing. Single- click the OK button to continue.  Select the theme in which you want to create the systematic grid cell polygons and create random sample points. Enter the cell size for the systematic grid in meters. In this example, the user entered 1609 meters (1 mile). In other words, there will be a single random point located within each 1 mile by 1 mile square area (refer to page 26). continue    Sample Point Generator (SPGen): Users Manual Page 23

  26. SAMPLE Point Generator 5  Make Systematic Grid Cell Polygons continued from page 23  The results of creating the systematic grid cell polygons. Notice that the system creates systematic cells around any combination of selected polygons or, if no polygons are selected, SPGen will create systematic cells over the entire theme extent.  Sample Point Generator (SPGen): Users Manual Page 24

  27. SAMPLE Point Generator 5A  Non-Aligned Systematic Points: Random Within Cell Definition Sample points are placed randomly within each theme grid cell to give comprehensive coverage and maintain a random structure to the sample points. This option is useful when a the user wants to sample “evenly” across an area (polygon) while still maintaining randomness required for statistical analysis.   From the Random Points pull-down menu, select the 5A  Non-Aligned in Systematic Points: Random Within Cell option.  From the Select Systematic Cell Theme popup window, select the systematic theme shape file and single-click the OK button.  From the Select Sample Point Theme popup window, select the sample point theme and single-click the OK button. The system will then begin to create a random sample point within each grid cell polygon. Refer to the next page typical results for this random sample routine. continue    Sample Point Generator (SPGen): Users Manual Page 25

  28. SAMPLE Point Generator 5A  Non-Aligned Systematic Points: Random Within Cell continued from page 25  Results of the non-aligned systematic random points within cell function.  Sample Point Generator (SPGen): Users Manual Page 26

  29. SAMPLE Point Generator 5B  Aligned Systematic Points: Centered Within Cell Definition A single random point is placed within the center of each grid cell, creating a complete regular pattern distribution of sample points.The dimension of the grid cell is the distance between points. This option is useful when when a regular sampling process is required and terrain allows.   From the Random Point pull-down menu, and select the 5B  Aligned Systematic Points: Centered Within Cell option.  From the Select Systematic Cell Theme popup window, select the systematic theme shape file and single-click the OK button.  From the Select Sample Point Theme popup window, select the sample point theme and single-click the OK button. The system will then begin to create a random sample point within each grid cell polygon. See the next page for typical results of this random sample routine. continue    Sample Point Generator (SPGen): Users Manual Page 27

  30. SAMPLE Point Generator 5B  Aligned Systematic Points continued from page 27  The results of the aligned systematic random points function. This option creates a completely regular pattern using the center of the cell as the point location.  Sample Point Generator (SPGen): Users Manual Page 28

  31. SAMPLE Point Generator 6A  Random Sampling from Existing Sample Points Definition This function allows the user to randomly select a user-entered number of points from an existing sample point theme. Use this when to resample a population in order to make inference about changes that have taken place in the population over a given time period.   From the Random Points pull-down menu, select the 6A  Select Random Points From The Sample Point Theme option.  Select the sample point theme that contains the input sample points you want to select from and single-click the OK button. The user enters the number of points to select from the existing sample point theme. In this example, the user entered 100 random points to select from the sample point theme, which contains 411sample points. Single-click the OK button. The system then randomly selects the desired number of points. The user can create a new point file from the selected polygons, or delete some of the selected points. continue    Sample Point Generator (SPGen): Users Manual Page 29

  32. SAMPLE Point Generator 6A  Random Sample from Existing Sample Points Continued from page 29  Results of the random selection of points from the existing sample points theme. In this view, dark points represent the original, non- selected points in the points theme, and light points represent selected sample points.  Sample Point Generator (SPGen): Users Manual Page 30

  33. SAMPLE Point Generator  Creating an ASCII file of Random Point Coordinates Definition Coordinates for sample points can be used in a GPS with the ability to upload coordinates in an ASCII format. The following instructions describe the process of exporting the sample point theme’s table to a comma-delimited text file (ASCII). Note: This is an ArcView function not tied to the random points generation routine. Details are available in ArcView documentation.   Set the Sample Points theme as the active theme within the View's theme table of Contents.  Click on the Open Table of Active Theme Button to open the table of the Sample Points Theme. The Sample Point Table appears. continue   Sample Point Generator (SPGen): Users Manual Page 31

  34. SAMPLE Point Generator Creating an ASCII file of Random Point Coordinates continued from page 31   From the File menu pull-down, select the Export function.  The Export Table popup window appears. Select the Delimited Text option and single-click the OK button to continue. The Export Table browse and file name popup window appears. Browse to the proper directory to store the new text file and name the file. Click the OK to complete the process. The new text file has now been written. continue    Sample Point Generator (SPGen): Users Manual Page 32

  35. SAMPLE Point Generator Creating an ASCII file of Random Point Coordinates continued from page 32   Example of the exported sample points text file as viewed in MS Notepad. This file can be modified by deleting any unwanted information except the point ID number, X coordinate, and Y coordinate; then it is ready for upload into a GPS.  Another method is to load the comma delimited text file into MS EXCEL, delete the extraneous columns, and save again as a text file (as seen in example )   Sample Point Generator (SPGen): Users Manual Page 33

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