Viewshed Points Tool

Overview

The Viewshed Points Tool generates spatially distributed observation points within selected polygon boundaries for viewshed and visibility analysis. This tool supports both manual point placement and automatic grid-based random generation, with server-side persistence for long-term tracking and analysis.

Key Features

• Target Polygon Selection: Click polygons from any visible polygon layer (Feature Layer or Map Image Layer)
• Manual Point Placement: Draw reference points directly on the map by clicking
• Automatic Grid Generation: Generate evenly distributed points within selected polygons with configurable point count and rotation angle
• Area-Based Point Limits: Maximum points adjust automatically based on total selected area (10 points under 50 ha, 15 points at 50 ha and above)
• Server Persistence: Save generated points to the database with a unique visibility number
• Delete by Number: Remove previously saved point sets by their visibility number
• Map Image Layer Support: Select polygons from server-based layers with result cycling through overlapping features

Before You Start

1. Ensure at least one polygon layer is visible on the map
2. Click the Viewshed Points Editor button (viewshed icon) in the toolbar to open the panel

How to Use

Step 1: Select a Target Layer

Choose a visible polygon layer from the Target Layer dropdown. The list includes all Feature Layers with polygon geometry and Map Image Layers with polygon sublayers currently visible on the map.

INFO

If the dropdown is empty, ensure at least one polygon layer is turned on in the Layer Panel.

Step 2: Select Target Polygons

1. Click the Select Target Shape button (cursor icon) to activate selection mode
2. Click polygons on the map to select them — selected polygons are highlighted
3. Click a selected polygon again to deselect it
4. The Total (ha) display updates as you add or remove polygons

For Map Image Layer data, clicking the same location cycles through overlapping polygon results. A notification shows which result is selected (e.g., "Selected polygon from LayerName (feature 1 of 3)").

Step 3: Place or Generate Points

You have two options for creating viewshed points:

Option A — Manual Placement:

1. Click the Draw Reference Point button (pin icon) to activate drawing mode
2. Click on the map to place individual observation points
3. Each point appears as a marker on the map
4. Click the draw button again to deactivate drawing mode

Option B — Automatic Generation:

1. Set the Number of Points value — default is 10, limited by area (see limits below)
2. Optionally set a Rotation Angle (0–180°) to rotate the point grid
3. Click the Generate button
4. Any previously generated or manually placed reference points are cleared before the new points are created
5. Points are distributed within the selected polygon boundaries using a grid algorithm

INFO

Point limits are based on total selected area: maximum 10 points when total area is under 50 ha, or 15 points when area is 50 ha or above.

Step 4: Save Points

1. After placing or generating points, click the Save button
2. Points are saved to the server and assigned a unique visibility number
3. A success notification displays the assigned number
4. The Viewshed Points layer refreshes to show the saved data

Resetting

Click the Reset button to:

• Clear all selected polygons from the map
• Remove all placed or generated reference points
• Deactivate selection and drawing modes
• Return to a fresh state

Deleting Saved Points

To remove a previously saved set of viewshed points:

1. Enter the Visibility Number in the delete section (red border area at bottom of panel)
2. Click the Delete button (trash icon) — the button is disabled until a number is entered
3. Review the confirmation dialog showing the number to be deleted
4. Click Delete to confirm or Cancel to abort

DANGER

Deleting viewshed points is permanent and cannot be undone. Always verify the visibility number before confirming.

Troubleshooting

Issue	Solution
No layers in dropdown	Ensure at least one polygon layer is visible on the map
Cannot select polygons	Click the Select Target Shape button to activate selection mode
Generate button produces few points	Reduce the number of points or select a larger polygon area
Save fails	Ensure at least one reference point is placed before saving
Delete fails	Verify the visibility number exists and try again
Map Image Layer polygons not working	Verify the layer has visible polygon sublayers
Points exceed limit	Only the first 15 points are saved; reduce point count

See Also

• Plot Random Tool — Similar polygon selection and point generation for plot sampling
• View Point Editor — Manage observation points with bearing analysis
• Concepts: FeatureLayer vs MapImageLayer — Understanding layer types used for polygon selection