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

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


Authors

Vern Thomas, FHTETMarla Downing, FHTET

Robin Reich, Colorado State University



The Sample Points Generator (SPGen) ArcView application allows the user to quickly create sample pointswithin 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.

Page 1

Random Point Generator Options


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 thetheme’s overall extent only where they fall within any theme polygon feature. From theMALE SAMPLE POINTS pull-down, select1A 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 windowand single-click the OK button. continue

Page 2

SAMPLE Point Generator

NOTE: You can usethis function withsingle polygon themes (e.g., forestboundary).


1A Random Points Within Theme Extent: CLASSIC

continued from page 2

The Enter The Number of Sample PointsTo 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 typicalof a random point pattern.

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1B Random Points Within Theme Extent: MIN DISTANCE

DefinitionRandom 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

Page 4




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 popupwindow 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 andsuggests the greatest value that the minimum distance should be set. In this example, anyvalue less than 2749 meters should workwithout loosing sample points due to too many sample point for a particular area basedon the minimum distance entered.

The Enter The Number of Sample PointsTo 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’sprojection so you will know the correct unitsto enter for minimum distance. (continue )

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 amaximum number of sample points to enter.In this example, the system estimates that themaximum number of sample points is 218.This number is based on the entered minimumdistance enter in the previous step and shouldbe used as a guide only. In our example, weentered 100 sample points (well under theestimates maximum).

Typical results of using the 1B Random Sample Points: MIN DISTANCE function.Notice that the pattern of the sample pointsincludes 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).

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Page 7

2A Points Within Selected Polygon(s): CLASSIC

DefinitionTrue 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 toreceive 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


Page 8



The Select Polygon Theme popupwindow 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 buttonto continue.

Enter the total number of sample points tobe placed within the selected polygons and single-click the OK button. In this example,the user entered 20 sample points. Thesystem then begins to create the random sample points. See the next page for the results of the random point generation ().

continue



Page 9

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 noticethat 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.





Page 10

2B Points Within Selected Polygon(s): MIN DISTANCE

DefinitionRandom 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 toplace 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



Page 11



From the Select Polygon Theme popupwindow, 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 tocontinue.

Enter the minimum distance betweensample 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 theselected polygons. Use this as a guide, not an absolute value. It is best to experiment with different minimum distances. continue


Estimated Minimum Distance


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Enter the number of sample points to create within the selected polygons.

NOTE: SPGen calculates the maximumNumber of sample points that can be createdgiven the area of the selected polygons andthe minimum distance entered in theprevious step. In the example to the right,SPGen has estimated that the user may entera maximum of 28 sample points. In this case we entered 20 sample points. Single clickthe OK button to continue. NOTE: It is important to know your data’sprojection so you will know the correct unitsto 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.





Page 13

3A Equal Number Random Points in Polygons: CLASSIC

DefinitionThe 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 Points pull-down menu, select the 3A Random Sample Points: BASIC option.

From the Select POLYGON Theme popupwindow, select the polygon theme to receive random sample points. Single-click the OKbutton 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 createsample points in every polygonin the theme unless there is a selected set of polygons. If thereis, it will create sample points only in the selected polygons.


Page 14

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” asthe number of random points to be placed in each of the theme’s polygons.

Typical random sample points results using the 3A Equal Number RandomPoints in Polygons: CLASSIC function.

NOTE: The points will look clustered in smaller polygons and generally more widely spaced in larger polygons.


3A Equal Number Random Points in Polygons: CLASSIC



Page 15

From the Random Points pull-down menu, select the 3B Random Sample Points: Minimum Distance option.

From the Select Polygon Theme pop-upwindow, select the polygon theme to receive sample points.

From the Select Sample Point Theme pop-up window, select the sample point theme. continue

3B Equal Number of Random Points in Polygons: MINIMUM

DISTANCE

DefinitionThe 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!!!



Page 16

3B Equal Number of Random Points in Polygons: MINIMUM

DISTANCE


Enter the number of random points to beplaced in each polygon and click OK. In thiscase, we want 5 sample points per polygonregardless of polygon area.

Enter the minimum distance betweensample points in meters. In this example, the user entered 800 meters (~1/2 mile). Noticethat SPGen estimates the the largest minimumdistance based on the smallest polygon in the theme. In this case, however, the user desires800 meter minimum distance.

A report box may appear if some polygonsdid not receive the allotted number of points. This may occur if a polygon has too small anarea to accommodate the number of samplepoints with the minimum distance. You canchoose to keep the points or reduce theminimum distance or reduce the numberof points (or both) and rerun.

Typical results of 3B Equal Number ofRandom Points in Polys: MIN DISTANCE.


NOTE:It is important to know your data’sprojection so you will know the correct units to enter for minimum distance.


Page 17

4A Area Weighted Probability Random Points: CLASSIC

DefinitionThe 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 variableof interest is correlated to size of the polygonsuch as forest surveys where the larger standswill contribute more to the overall mean thanthe smaller stands. If the variable of interest isNot correlated to to polygon size, then the variance may be larger than if you did a simple random sample.

From the Random Points pull-down menu, select the 4A Random Sample Points: CLASSIC option.

From the Select Polygon Theme popupwindow, select the theme containing the selected polygon(s) to receive random samplepoints. 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.

Page 18

4A Area Weighted Probability Sample Points: CLASSIC


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 pointsto create within the theme and single-clickthe OK button. The system will then beginto create sample points.

Results of the Area Weighted Probabilityrandom sample point process. Notice that the pattern of the sample points is random andthat some of the smaller polygons contain nosample points while the larger polygonscontain more points.



Page 19

4B Area Weighted Probability: MINIMUM DISTANCE

DefinitionRandom 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 pointsare then distributed within the polygonswhere the larger the polygon, the more probability that that polygon will have arandom 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 Points pull-down menu,select the 4B Random Sample Points:MIN DIST option.

continue



Page 20

4B Area Weighted Probability:MINIMUM DISTANCE


From the Select Polygon Theme popupwindow, select the theme containing the selected polygon(s) to receive randompoints. 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 pointsto create within the theme and single-clickthe OK button.

Enter the minimum distance betweensample points in meters. In this example, the user entered 1609 meters (1 mile). SPGen will then begin to create samplepoints. Notice the system estimates thelargest minimum distance to use given thearea of the theme. In this example, itsuggests that the user may use a minimumdistance of 2749 meters or less.

continue



Page 21

4B Area Weighted Probability: MINIMUM DISTANCE


Typical results of the Area Weighted Probability: Min Distance random point function. Notice that the pattern of the sample points appears fairly regular, thoughit 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 greatgiven 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-upa warning message informing the user thatit cannot populate all requested sample pointsand that the user should either reduce the minimum distance or the number of sample points.



Page 22

5 Make Systematic Grid Cell Polygons

DefinitionA 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 toplace 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



Page 23



From the Select Systematic Cell Theme popup window, select the systematic celltheme (this shape file comes as part of yourZIP 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 tocreate the systematic grid cell polygons andcreate 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



Page 24



The results of creating the systematic grid cell polygons.

Notice that the system creates systematic cellsaround any combination of selected polygonsor, if no polygons are selected, SPGen willcreate systematic cells over the entire themeextent.



Page 25

From the Random Points pull-down menu,select the 5A Non-Aligned in Systematic Points: Random Within Cell option.

From the Select Systematic Cell Themepopup window, select the systematic themeshape file and single-click the OK button.

From the Select Sample Point Themepopup window, select the sample pointtheme and single-click the OK button. The system will then begin to create arandom sample point within each grid cellpolygon. Refer to the next page typical resultsfor this random sample routine.

continue

5A Non-Aligned Systematic Points: Random Within Cell

DefinitionSample 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.



Page 26

Results of the non-aligned systematicrandom points within cell function.

5A Non-Aligned Systematic Points: Random Within Cell




Page 27

From the Random Point pull-down menu,and select the 5B Aligned Systematic Points: Centered Within Cell option.

From the Select Systematic Cell Themepopup window, select the systematic themeshape file and single-click the OK button.

From the Select Sample Point Themepopup window, select the sample pointtheme and single-click the OK button. The system will then begin to create arandom sample point within each grid cellpolygon. See the next page for typical resultsof this random sample routine.

continue

5B Aligned Systematic Points:Centered Within Cell

DefinitionA 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.



Page 28

The results of the aligned systematicrandom points function. This option creates a completely regular pattern using the center of the cell as the point location.

5B Aligned Systematic Points




Page 29

6A Random Sampling from Existing Sample Points

DefinitionThis 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 containsthe input sample points you want to select from and single-click the OK button.

The user enters the number of pointsto 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



Page 30

6A Random Sample from Existing Sample Points


Results of the random selection of pointsfrom the existing sample points theme. In this view, dark points represent the original, non-selected points in the points theme, and lightpoints represent selected sample points.



Page 31

Creating an ASCII file of Random Point Coordinates

DefinitionCoordinates 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 activetheme within the View's theme table of Contents.

Click on the Open Table of Active ThemeButton to open the table of the Sample Points Theme.

The Sample Point Table appears.

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Page 32



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 namepopup window appears. Browse to the proper directory to store the new text fileand name the file. Click the OK to completethe process. The new text file has now been written.

continue



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Example of the exported sample pointstext 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, deletethe extraneous columns, and save again as a text file (as seen in example )



Documents

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