Observer Points Editor

Overview

The Observer Points Editor generates spatially distributed observation points within selected polygon boundaries for viewshed and visibility analysis. It supports both manual point placement and automatic grid-based generation, with server-side persistence so a set of points can be saved, reused, and analysed later.

Each saved set is identified by a unique visibility number. Those saved sets feed directly into the embedded Visibility Surface Analysis tool, which computes how many of a saved set's observers can see each part of the landscape.

Formerly "Viewshed Points Editor"

This panel was previously called the Viewshed Points Editor. It has been renamed to Observer Points Editor to match the terminology used across the visibility tools. The toolbar button and its viewshed icon are unchanged.

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 a Saved Set: Remove a previously saved point set by picking its visibility number from a dropdown
• Embedded Visibility Surface Analysis: Run a multi-observer visibility calculation on a saved set without leaving the panel
• 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 Observer Points Editor button (viewshed icon) in the toolbar to open the panel

INFO

Some screenshots and videos below show the panel's former name, Viewshed Points Editor — the layout and controls are unchanged.

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 observer 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 Point Count value — default is 10, limited by area (see limits below)
2. Optionally set a Grid 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 observer 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 a Saved Set

To remove a previously saved set of observer points:

1. In the delete section (red-bordered area at the bottom of the panel), open the Delete Saved Points (Vis Number) dropdown — it lists all saved visibility numbers, newest first, and defaults to the most recent
2. Select the number you want to delete
3. Click the Delete button (trash icon)
4. Review the confirmation dialog showing the number to be deleted
5. Click Delete to confirm or Cancel to abort

TIP

Choosing the number from the dropdown (instead of typing it) avoids mistyping a visibility number and deleting the wrong set. The dropdown refreshes to reflect the latest saved sets.

DANGER

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

Video Tutorials

Generating points automatically

Placing points manually

Deleting a saved set

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
No numbers in the Delete dropdown	You have no saved sets yet; save points first, then reopen the dropdown
Delete fails	Verify the visibility number still 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

Visibility Surface Analysis

The Visibility Surface Analysis tool answers the question "how many observers can see each spot on the ground?" For every cell inside an extent rectangle you draw, it computes how many of a saved observer set can see that cell — the cell's frequency — and draws the result as a colour-graded polygon layer. Areas visible to many observers appear in deep blue; areas seen by only one observer appear in light lavender; areas seen by none stay transparent.

Unlike the Line of Sight tool (a single observer), this tool works with a whole saved set of observer points at once — the sets you create and save above. It lives inside this editor as a collapsible block near the bottom of the panel:

• Expand the block to activate the tool and load your saved observer sets
• Collapse the block (or close this editor) to deactivate it and cancel any running job — a completed result stays on the map
• After you save or delete a set here in the editor, the tool's observer-set dropdown refreshes automatically

The calculation runs as an asynchronous geoprocessing (GP) job on the ArcGIS Server using a digital elevation model (DEM), so you can keep working while it processes.

Coordinate System

Observer points and the drawn extent are analysed in EPSG:28355 (GDA94 / MGA Zone 55), in metres. Horizon projects your saved points and the drawn box into this system for you automatically, so measurements are accurate regardless of the basemap projection.

Key Features

• Multi-Observer Visibility: Calculates, per cell, how many of a saved observer set can see it — not just yes/no visibility from a single point
• Saved Observer Sets: Choose an observer set by its visibility number — the same numbered sets you save above
• Draw-to-Bound Extent: Draw a rectangle on the map to bound the analysis area; the analysis radius is derived automatically from the box size (no manual radius to set)
• Adjustable Parameters: Set the observer height above ground and the cell size (detail), with optional advanced refraction and vertical-error settings
• Colour-Graded Result with Legend: The visibility surface is added as a proper map layer with a frequency colour ramp and matching Legend entry ("1 observer", "2 observers", …)
• Asynchronous Processing: Submit the job and monitor progress with real-time status updates, a message log, and a cancel option
• Extent Validation: Before submitting, the tool checks that your drawn extent actually overlaps the selected observer set, so you don't wait on a job that would return an empty surface
• Customisable Marker Colours: Observer markers and the extent rectangle follow your Target graphics style

Using the Tool

Expand the Visibility Surface Analysis block near the bottom of the panel to activate it and load your saved observer sets.

INFO

Collapsing the block or closing the Observer Points Editor deactivates the tool and cancels any running job. A completed result stays on the map so you can keep viewing it after you close the editor.

The block's subtitle reads "Compute the area visible from saved observer points." Until you draw an extent, Submit stays disabled and Radius shows a read-only "Auto (draw extent)" placeholder.

Step 1: Choose a Saved Observer Set

1. Open the Saved Observer Points (Vis Number) dropdown — it lists your saved observer sets, newest first (click the dropdown to refresh the list)
2. Select the set you want to analyse

Optionally, turn on Show only selected on map to filter the visibility-points layer so only the chosen set's points are displayed — useful for confirming you picked the right set before drawing an extent.

INFO

The observer points themselves are only fetched when you Submit. Selecting a set just tells the tool which points to use — it does not draw or move anything on its own.

Step 2: Set the Analysis Parameters

Parameter	Default	Range	Description
Observer Height (m)	1.5	0–500	Eye height above the ground at each observer point (1.5 m ≈ standing eye level)
Cell Size (m)	5	1–50	The analysis detail. A smaller value gives finer detail but takes longer; a larger value is faster but coarser
Radius (m)	Auto	50–20,000	Read-only — shows "Auto (draw extent)" until you draw an extent, then fills in automatically from the box (see Step 3)

Advanced parameters (optional — expand the Advanced row):

Parameter	Default	Range	Description
Refractivity Coefficient	0.13	0–1	Atmospheric refraction adjustment
Vertical Error (m)	0	0–1,000	Allowance for vertical error (RMSE) in the elevation model

Choosing a Cell Size

The default 5 m is a good balance of detail and speed. Lower it (toward 1–2 m) only when you need very fine detail, and raise it for a faster, coarser result over a large area.

Step 3: Draw the Analysis Extent

The extent rectangle bounds the area analysed and sets the radius automatically:

1. Click Draw Extent Rectangle (square icon)
2. A hint appears: "Click and drag on the map to draw the analysis rectangle."
3. Click and drag on the map to draw the box around the area of interest
4. The Radius field fills in automatically — it is calculated from the size of the box (half its diagonal, in true metres)

A status chip beside Analysis Extent shows Set once a rectangle is drawn. Click Clear (trash icon) to remove the extent and start again, or click Draw Extent Rectangle again to redraw.

TIP

Draw the extent over the observer set you selected. If the box doesn't overlap any of the chosen set's points, the tool will stop you at Submit (see below) — the result would otherwise be blank.

Step 4: Submit the Analysis

1. Make sure an observer set is selected and an extent is drawn — the Submit button enables when both are set and a valid radius has been derived
2. Click Submit (play icon)
3. The button shows a loading indicator while the job processes
4. Real-time status messages appear below the action buttons

"No Observers In Extent"

Before submitting, the tool checks that at least one point from the selected observer set falls inside your drawn extent. If none do (for example, you selected vis 366 but drew the box over vis 245's points), it shows a "No Observers In Extent" message and does not submit — saving you a wasted server round-trip that would return an empty surface. Redraw the extent over the correct set, or reselect the set that matches your box.

Monitoring job progress — while the job is running:

• A progress indicator shows the current status with friendly labels (e.g., "Submitted", "Processing", "Completed")
• The latest server message is displayed inline
• A message count badge appears — click it to open the full Job Messages dialog
• A Cancel button appears to abort the job if needed

Job Messages dialog — click the message count badge to open it:

• Draggable and resizable — position it anywhere on screen
• Non-modal — you can keep interacting with the map while viewing messages
• Messages are shown in a numbered, scrollable list with a monospace font
• Error messages are highlighted in red
• Auto-scrolls to the latest message as they arrive
• The heading reflects the job state (Processing, Completed, or Failed)

The dialog can also be opened after the job completes to review the full processing log.

Understanding Your Results

When the job completes successfully, the visibility surface is added to the map as a layer named "Visibility Surface Result" (inside a "Visibility Surface" group), and the map zooms to it. The polygons are coloured by frequency — the number of observers that can see each area:

• Light lavender → seen by a small number of observers (e.g. 1)
• Deeper blue → seen by progressively more observers
• Transparent (no fill) → not visible to any observer — these areas have no legend entry

Because the result is a proper map layer (not just drawn graphics), it appears in the Legend with a swatch per class — "1 observer", "2 observers", and so on, up to the maximum overlap — so you can read exactly what each colour means. Areas visible to no observer are left transparent and do not appear in the legend. In the Layer Panel you can toggle the result on/off and adjust its opacity with the slider.

Result stays on the map

A completed visibility surface remains on the map even after you collapse the block or close the Observer Points Editor, so you can keep it as a reference. Running the analysis again adds a fresh result; older kept results are renamed with a number ("Visibility Surface Result 1", "Visibility Surface Result 2", …) so they don't collide, and remain until you remove them from the Layer Panel.

Customising the Marker Colours

The observer markers and the extent rectangle both use your Target graphics style, editable in System → Graphics Styles (new colours apply the next time you run the analysis). The visibility-surface polygons use a fixed frequency colour ramp so the legend stays consistent.

Resetting the Tool

Click the block's Reset button to clear the observer markers and drawn extent, restore the height, cell size, and advanced parameters to their defaults, remove the current visibility-surface result, and clear the job status and messages.

Worked Example: How Visible Is a Proposed Site?

1. Above, save a set of observation points (note its visibility number)
2. Expand the Visibility Surface Analysis block
3. In Saved Observer Points (Vis Number), select the set you just saved
4. Leave Observer Height at 1.5 m and Cell Size at 5 m
5. Click Draw Extent Rectangle and drag a box around the area of interest (make sure it covers your observer points) — the Radius fills in automatically
6. Click Submit
7. Monitor progress via the inline status, or open the Job Messages dialog for full detail
8. When it finishes, inspect the colour-graded surface — deep-blue areas are visible to the most observers, and the Legend shows how many observers each colour represents

Visibility Surface Analysis — Troubleshooting

Issue	Solution
The tool controls are greyed out / nothing loads	Make sure the Visibility Surface Analysis block is expanded — it only activates on expand
No saved sets in the Vis Number dropdown	You have no saved observer points yet. Save a set above first, then click the dropdown to refresh
Submit button is disabled	Select an observer set and draw an extent rectangle; wait for the Radius to fill in and for any running job to finish
"No Observers In Extent" message	Your drawn extent doesn't overlap any point in the selected set. Redraw the box over the set's points, or select the set that matches your box
Radius stays empty after drawing	Redraw the extent — the radius is derived from the box; if drawing was interrupted, the value may not have been calculated
Result is empty or barely visible	The chosen observers may see very little inside the extent. Try a taller observer height, a smaller cell size, or an extent that better covers the terrain of interest
Result shows on the map but not in the Legend	Open the Legend panel and confirm the "Visibility Surface" layer is turned on
Job fails with an error	Open the Job Messages dialog to read the server error. Common causes are an extent outside the elevation data coverage or a temporary server issue
Cannot cancel a job	The Cancel button only appears while a job is actively running

Visibility Surface Analysis — FAQ

Q: What does the "frequency" colour mean? A: It is the number of observers in the selected set that can see a given area. A cell coloured for "3 observers" is visible from three of your saved observer points; a transparent cell is visible from none.

Q: How is this different from the Line of Sight tool? A: Line of Sight analyses visibility from a single observer point. Visibility Surface Analysis analyses a whole saved set of observer points at once and tells you how many of them can see each area.

Q: Why don't I set the radius myself? A: The radius is derived automatically from the extent rectangle you draw — it is half the box's diagonal, measured in true metres. This guarantees the analysis reaches every corner of the box, so you only need to draw the area you care about.

Q: Why did the tool refuse to submit? A: Most often because your drawn extent doesn't overlap the selected observer set ("No Observers In Extent"), or because an observer set or extent isn't set yet. Fix the flagged item and submit again.

Q: Can I change the colours of the surface? A: The frequency ramp is fixed so the legend stays meaningful across runs. The observer markers and the extent rectangle do follow your Target graphics style (System → Graphics Styles).

Q: How long does it take? A: Usually a short while, depending on the size of the extent, the cell size, and the number of observers. A very large extent or a very small cell size will take longer.

See Also

• Line of Sight — Single-observer visibility analysis
• Plot Random Tool — Similar polygon selection and point generation for plot sampling
• VR Calculator — Another asynchronous geoprocessing (GP) analysis tool
• Concepts: FeatureLayer vs MapImageLayer — Understanding layer types used for polygon selection