4.14.1. Block Triangulation

Block triangulation (bundles or independent models) provides the best internal strength as compared to the strip triangulation in radial triangulation method (Ackermann, 1975). The available tie points in consecutive strips assists in the roll angle recovery which is one of the weaknesses in the strip triangulation.

Block triangulation is a method used to analyze aerial photographs by forming a network of overlapping images that allows for more precise measurements of the terrain. Unlike strip triangulation, which processes images sequentially, block triangulation uses bundles of images which create a more rigid and accurate structure, improving internal consistency and reducing errors.

Think of block triangulation like putting together a 3D puzzle. Just as each piece must fit together perfectly to see the complete picture, each photograph needs to align accurately with the others to form a precise model of the terrain.

In terms of computational aspect, the aerial triangulation methods are categorized as: analog, semi-analytical, analytical, and digital triangulation. The analytical and digital aerial triangulation methods tend to be more accurate than the analog or semi analytical aerial triangulation.

Aerial triangulation can be performed using various methodologies:

1. Analog Aerial Triangulation: Uses traditional stereo-plotters for model orientation, relying on manual adjustments.
2. Semi-analytical Aerial Triangulation: Combines analog and digital approaches, allowing for more precise alignment between stereo pairs through coordinate transformations.
3. Analytical Aerial Triangulation: Uses sophisticated software and image coordinates for creating three-dimensional point sets.
4. Digital Aerial Triangulation: Fully automated and allowing for real-time adjustments with high accuracy using digital images.

Imagine assembling a bookcase. Different methods can be used: measuring by hand (analog), using a level tool for precise alignment (semi-analytical), laser levels for perfect angles (analytical), or even smart tools that tell you when everything is straight (digital). Each method has its levels of accuracy and efficiency.

Analytical aerial triangulation can be carried out using analytical relative orientation of each model first, and then connecting the adjacent models to form a continuous strip which is finally adjusted to ground controls.

In analytical aerial triangulation, the process begins by aligning each model relative to one another. This placement is critical as it ensures that overlapping areas between models correctly merge together. Once this is done, adjustments are made to incorporate known ground control points, refining the model for increased accuracy.

Consider this method like building a road with multiple segments. Each segment must correctly connect at the joints. By ensuring that each piece fits the next perfectly while also adjusting to align with landmarks (ground controls), a straight and accurate road can be achieved.

It uses a photogrammetric workstation which can display digital images. Digital aerial triangulation is similar to analytical aerial triangulation but here all the measurements are carried out utilizing the digital photographs.

Digital aerial triangulation incorporates modern software and technology, allowing for the rapid processing of aerial images. The measurements taken from digital photographs can be synchronized in a single solution, enhancing the overall speed and accuracy of the mapping process. This method capitalizes on technological advancements to produce effective results.

Think of digital aerial triangulation as using a GPS navigation system in your car. Instead of manually looking at a map, the GPS quickly gathers real-time data and directs you to your destination efficiently, demonstrating greater accuracy and speed.

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