Lesson Objectives:

1. Understand the Importance of Targeting in Drone Mapping – Explain why accurate targeting is crucial for photogrammetry and LiDAR applications.
2. Identify Different Types of Targets – Recognize and differentiate between checkerboard targets, chevron targets, reflective tape, and LiDAR-specific targets.
3. Explain Target Placement Strategies – Understand the best practices for placing targets to ensure high accuracy in mapping.
4. Describe the Role of Survey Nails in Targeting – Explain how survey nails help improve measurement accuracy.
5. Compare Photogrammetry and LiDAR Targeting Methods – Identify the differences in targeting requirements between photogrammetry and LiDAR mapping.
6. Understand the Role of Check Shots – Explain how check shots contribute to accuracy validation in drone mapping.

Topics Covered:

Introduction to Targeting in Drone Mapping

• Importance of accurate targeting
• Role of targets in photogrammetry and LiDAR mapping

Types of Targets Used in Drone Mapping

• Checkerboard targets
• Chevron targets
• Reflective tape and paint
• LiDAR-specific reflective targets

Survey Nails and Their Role in Accuracy

• Purpose of a survey nail in target placement
• How survey nails improve measurement accuracy

Target Placement Strategies

• Ideal target locations for photogrammetry
• Target placement for LiDAR mapping
• Use of perimeter targets when interior placement is not possible

Check Shots and Their Function

• Horizontal check shots and validation using existing features
• Vertical check shots and their role in verifying elevation data

Surface Considerations for Targeting

• Hard surface targeting using tape and paint
• Soft surface targeting using staked-down targets

Best Practices for Drone Mapping Accuracy

• How to determine the number of targets needed
• Adjusting target types and placements based on mapping needs

Introduction to Targeting in Aerial Mapping

In aerial mapping, precise targeting is essential for ensuring accurate geospatial data. Whether using photogrammetry or LiDAR technology, carefully selecting and placing targets can significantly impact the quality of the final dataset. Different types of targets, materials, and placement strategies are used to optimize accuracy based on the type of terrain, mapping method, and flight speed.

Types of Targets Used in Aerial Mapping

There are several types of targets used in aerial mapping, depending on the data collection method:

1. Checkerboard and Chevron Targets

• Checkerboard patterns are commonly used in photogrammetry because they provide high-contrast, easily recognizable features for aerial imagery processing.
• Chevron targets, shaped like arrows, are also useful for marking key points on the ground.
• These targets are often secured with pins, particularly on soft surfaces such as dirt or turf, to prevent movement.

2. Reflective Targets for LiDAR Applications

• Reflective targets, such as hexagons with reflective circles, are ideal for LiDAR mapping.
• The reflectivity of these targets ensures that they appear prominently in the intensity view of LiDAR data.
• Large targets are preferable for high-speed flights (30+ mph), as they provide enough data points for precise location identification.
• Even if the laser does not capture all target features in a single pass, a strong reflection from multiple angles enables accurate alignment.

3. Reflective Tape and Painted Targets

• On hard surfaces such as pavement, reflective tape and painted targets (e.g., checkerboards, chevrons) are commonly used.
• A survey nail is typically placed at the center of these targets to ensure a precise reference point for measurements.
• In forested or greenfield sites with no clear areas for interior targets, these markers are often placed along perimeter roads.

Placement Strategies for Targeting

Proper target placement is crucial for minimizing error and ensuring accuracy in aerial mapping. Placement strategies vary slightly depending on whether photogrammetry or LiDAR is used.

1. Photogrammetry Target Placement

• A well-distributed set of targets improves the accuracy of photogrammetric models.
• Targets should be positioned with at least one near the center of the survey area and additional targets distributed evenly throughout.
• Targets should avoid being placed at extreme edges but should still be positioned near the corners to provide sufficient coverage.
• A typical setup includes at least four to six targets, depending on the survey area size and shape.

2. LiDAR Target Placement

• LiDAR follows similar principles but emphasizes target reflectivity for enhanced visibility in point clouds.
• Like photogrammetry, LiDAR targeting benefits from well-distributed markers with check shots to validate data integrity.

The Importance of Check Shots

Check shots are additional data points used to validate aerial mapping accuracy. Unlike standard targets, check shots do not require predefined markers and can be natural or artificial features within the survey area.

1. Horizontal Check Shots

• These are used to validate the accuracy of positional (X, Y) data.
• Features such as road stripes, turn arrows, and stop bars serve as reference points.

2. Vertical Check Shots

• Used to validate elevation (Z) data in LiDAR and photogrammetric surveys.
• Any known elevation points, such as measured ground features or structures, can serve as vertical check shots.

Conclusion

Effective targeting and check shot placement are fundamental to producing accurate aerial mapping data. Whether using photogrammetry or LiDAR, choosing the right target materials, securing them properly, and distributing them strategically across the survey area ensures high-quality results. By incorporating check shots, surveyors can further validate and refine their data, reducing errors and improving overall mapping accuracy.

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