How to Use Survey Photo Pro

Complete guide to getting accurate measurements from your photos

Getting Started

Step 1: Create Your Account

Visit phototool.centerlinegroup.app
Click "Start 7-Day Free Trial"
Enter your name, email, and create a password
Complete payment setup (you won't be charged during the 7-day trial)
You're ready to start measuring!

Step 2: Download the Calibration Target

From your Dashboard, find the "Calibration Target" card
Click "Download PDF"
Print the target on standard letter paper (8.5" × 11")
Important: Print at 100% scale - do not resize or "fit to page"

The Calibration Target

The calibration target is the key to accurate measurements. It's a 6" × 6" grid with a special ArUco marker that the system uses to calculate scale and perspective.

Printing Instructions

Paper: Standard white paper (letter size)
Scale: Print at 100% (actual size) - DO NOT select "fit to page"
Color: Can be printed in black and white
Quality: Standard print quality is fine

Target Care Tips

• Keep the target flat (don't fold or crease it)
• Laminate it for durability in the field
• Make multiple copies for different job sites
• The target must remain exactly 6" × 6" to work

Visibility Range

The target is designed to be visible from approximately 20+ feet away, depending on camera quality, lighting conditions, and photo resolution.

Taking Photos

Best Practices

Place the Target in the Scene

• Position the target flat against the surface you want to measure
• The target should be in the same plane as the items you're measuring
• Make sure all 4 corners of the target are visible

Ensure Good Lighting

• Avoid harsh shadows across the target
• Natural daylight works best
• Avoid glare or reflections on the target

Take a Clear Photo

• Hold the camera steady or use a tripod
• Make sure the target is in focus
• Higher resolution = more accurate measurements

Angle Considerations

• The system automatically corrects for perspective
• You can photograph at an angle if needed
• Extreme angles (>60°) may reduce accuracy

What NOT to Do

❌ Don't photograph the target at an extreme angle
❌ Don't let the target get partially blocked
❌ Don't use a blurry or out-of-focus photo
❌ Don't photograph through glass or screens
❌ Don't resize or edit the photo before uploading

Creating Projects

Projects help you organize photos by job site, client, or task.

To Create a New Project:

From the Dashboard, click "New Project"
Enter a Project Name (e.g., "123 Main Street Inspection")
Add an optional Description
Click "Create Project"

Organization Tips

• Create one project per job site or client
• Use descriptive names you'll recognize later
• Add dates to project names if helpful (e.g., "Smith Residence - Feb 2026")

Calibrating Your Photos

Calibration tells the system the real-world scale of your photo.

Automatic Calibration (Recommended)

Click on a photo to open the editor
If the ArUco marker is detected, calibration happens automatically
You'll see a message confirming successful calibration

Manual Calibration

If automatic detection fails, you can calibrate manually:

Click "Calibrate" in the control panel
Click on the 4 corners of the calibration target in your photo
Place points in this order: Top-Left → Top-Right → Bottom-Right → Bottom-Left
The system will calculate the scale based on the known 6" × 6" target size

Fine-Tuning Calibration Points

• Click on any placed point to select it
• Use Arrow Keys to nudge the point (1px, 5px, or 10px steps)
• Press Enter to confirm the position
• Click "Reset Points" to start over

Known Dimensions (Reference Points)

Sometimes you take a photo and later realize you missed a measurement. If you have any known dimensions in the photo—measurements you took in the field with a tape measure—you can enter them as reference points to improve accuracy throughout the photo.

When to Use Reference Points

• You missed a dimension and need to measure from the photo
• You want to verify or improve accuracy in a specific area
• The calibration target is far from what you need to measure
• You took field measurements and want to use them as ground truth

How to Add a Reference Point

Open your photo in the editor
Click the "Reference" tool (blue anchor icon) in the toolbar
Click to place the first point
Use arrow keys to fine-tune, then press Enter to confirm
Click to place the second point
Use arrow keys to fine-tune, then press Enter to confirm
Enter the known distance (e.g., "4'-6"", "54", or "4.5'")
Optionally add a label (e.g., "doorway width")
Click "Save Reference"

Supported Distance Formats

Feet-Inches:

• 4'-6" (4 feet 6 inches)
• 4' 6"
• 4'6"

Inches Only:

• 54 (54 inches)
• 54"

Feet with Decimal:

• 4.5' (4 feet 6 inches)
• 4.5

Good Reference Points

• Doorway widths (usually 32" or 36")
• Window dimensions
• Wall lengths you measured with a tape
• Standard-size objects (4'x8' drywall, etc.)
• Distances between fixtures

Avoid As References

• Estimated or guessed measurements
• Objects on a different plane/surface
• Very short distances (<6 inches)
• Objects that may have moved

How It Improves Accuracy

When you add reference points, the system uses Inverse Distance Weighting to calculate measurements. This means:

• Measurements closer to a reference point use that reference's scale factor more heavily
• Multiple references create a "mesh" of accurate calibration across the photo
• You can achieve ±1/4" accuracy even far from the calibration target

Consistency Warnings

If you add multiple reference points that disagree by more than 5%, the system will show a yellow warning. This usually means one of the reference measurements is incorrect, or the references are on different planes. Double-check your field measurements!

Pro Tip: Combine with Calibration Target

For best results, use both a calibration target and reference points. The target provides the baseline calibration, and reference points fine-tune accuracy in specific areas of the photo. This is especially useful when measuring far from the target.

Taking Measurements

Measuring Length (Line Tool)

Make sure your photo is calibrated
Select the "Line" tool from the control panel
Click to place the start point
Use arrow keys to fine-tune position, then press Enter
Click to place the end point
Use arrow keys to fine-tune, then press Enter
The measurement appears on the line in construction format

Reading Measurements

Measurements are displayed in construction format:

• Feet and inches: 4'-6" (4 feet, 6 inches)
• Fractions: 4'-6 1/2" (4 feet, 6 and a half inches)
• Small measurements: 8 3/16" (8 and three-sixteenths inches)

Calculating Areas

Measuring Area (Area Tool)

Make sure your photo is calibrated
Select the "Area" tool from the control panel
Click to place points around the perimeter of the area
Fine-tune each point with arrow keys, press Enter to confirm
The area is calculated and displayed in square feet

Area Display Format

Areas are shown in square feet (e.g., 12.5 sq ft)

Using the Photo Editor

Navigation Controls

Action	How To
Zoom In	Click "+" button or scroll wheel up
Zoom Out	Click "-" button or scroll wheel down
Pan	Click and drag on the photo
Reset Zoom	Click "Reset Zoom" button
Recenter	Click "Recenter" button (keeps current zoom)

Zoom Levels

• Minimum: 10%
• Maximum: 2000%
• Use high zoom for precise point placement

Draggable Control Panel

• Click and hold the header bar
• Drag to any position on screen
• Release to drop in place

Preview Lines

When placing measurement points, a dashed preview line shows where your measurement will go. This helps you align measurements before committing.

Exporting PDF Reports

To Export a PDF:

Open the project containing your photos
Click "Export PDF" button
The PDF will download automatically

PDF Contents

• Cover page with project details
• Each photo on its own page
• Measurements and annotations visible
• Date and time of export

Using Multiple Targets

For larger areas, using multiple calibration targets significantly improves measurement accuracy. The system uses each target to create localized calibration zones, reducing error accumulation over distance.

Target Quantity Guidelines

Area Size	Targets Needed	Expected Accuracy
Up to 10' × 10' (100 sq ft)	1 target	±1/8" near target, ±1/4" at edges
Up to 20' × 20' (400 sq ft)	2 targets	±1/4" throughout area
Up to 30' × 30' (900 sq ft)	3 targets	±3/8" throughout area
Up to 40' × 40' (1600 sq ft)	4 targets	±1/2" throughout area
Larger than 40' × 40'	5+ targets or multiple photos	±1/2" to ±1"

How to Place Multiple Targets

Print multiple copies of the calibration target
Space targets evenly across the area you're measuring
Place targets at opposite ends of your measurement area
Ensure all targets are on the same plane (floor, wall, etc.)
For rooms, place one target near each corner you need to measure

Target Placement Examples

20' Room: One target near each end
30' Room: Triangular pattern (one at each end, one in middle)
Large Open Space: Grid pattern, ~15-20' apart
L-Shaped Room: One target in each wing plus one at the corner

Pro Tip: Measure Close to Targets

Always try to take measurements close to a calibration target rather than far away. If you need to measure something far from any target, consider adding another target nearby for that measurement.

LiDAR App Integration

For maximum accuracy on larger projects, you can combine Survey Photo Pro with LiDAR scanning apps. LiDAR (Light Detection and Ranging) uses laser technology to capture precise 3D measurements.

Compatible LiDAR Apps

Magicplan

Full REST API integration. Export floor plans and measurements as CSV/XML.

Polycam

Export raw 3D data including depth maps and camera poses.

Canvas (Twindo)

Export DWG/SKP files for CAD integration.

Hybrid Workflow: LiDAR + Photo Measurements

Scan with LiDAR: Use Magicplan or Polycam to capture the overall space
Export measurements: Download the CSV/XML data from the LiDAR app
Import to Survey Photo Pro: Upload the LiDAR data to use as reference
Add detail photos: Take photos with calibration targets for specific details
Combine data: Use LiDAR for overall dimensions, photos for fine details

When to Use LiDAR

• Large spaces (500+ sq ft)
• Complex room shapes
• Multiple rooms to measure
• Need 3D floor plans
• Critical accuracy (sub-1/8")

When Photo Measurement is Better

• Single room or small area
• Quick field verification
• Detail measurements (molding, fixtures)
• Areas LiDAR can't reach
• Budget-conscious projects

LiDAR Device Requirements

LiDAR scanning requires a device with a LiDAR sensor:

• iPhone: iPhone 12 Pro or newer (Pro models only)
• iPad: iPad Pro 2020 or newer
• Android: Limited devices (Samsung Galaxy S20 Ultra, etc.)

Tips for Best Results

For Maximum Accuracy

✅ Place target flat against the measurement surface
✅ Ensure target is in the same plane as what you're measuring
✅ Use good lighting without harsh shadows
✅ Take sharp, focused photos
✅ Use the highest resolution your camera offers
✅ Zoom in when placing measurement points
✅ Use arrow keys for sub-pixel precision

Common Issues & Solutions

Issue	Solution
Target not detected	Ensure all 4 corners are visible and in focus
Measurements seem off	Re-calibrate; make sure target is flat
Photo won't load	Refresh the page; check internet connection
Can't zoom in enough	Maximum zoom is 2000%
Points hard to place	Zoom in; use arrow keys for fine adjustment

Accuracy Expectations

• Best case: ±1/16" accuracy when target is close and clearly visible
• Typical: ±1/8" to ±1/4" for most field conditions
• Factors: Distance from target, photo resolution, target flatness, lighting

Quick Reference: Keyboard Shortcuts

Photo Editor

↑ ↓ ← → Nudge selected point
Enter Confirm point placement
1 5 0 Set nudge amount (1px, 5px, 10px)

Workflow Summary

Print calibration target at 100% scale
Place target in scene (flat, visible)
Photograph with target in frame
Upload to a project
Calibrate (auto or manual)
Measure using Line and Area tools
Export PDF report

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