Skip to main content

Photogrammetry


Photogrammetry is the science of taking measurements from photographs—especially to create maps, models, or 3D images of objects, land, or buildings.

Imagine you take two pictures of a mountain from slightly different angles. Photogrammetry uses those photos to figure out the shape, size, and position of the mountain—just like our eyes do when we see in 3D!

Concepts and Terminologies

1. Photograph

A picture captured by a camera, either from the ground (terrestrial) or from above (aerial or drone).

2. Stereo Pair

Two overlapping photos taken from different angles. When seen together, they help create a 3D effect—just like how two human eyes work.

3. Overlap

To get a 3D model, photos must overlap each other:

  • Forward overlap: Between two photos in a flight line (usually 60–70%)

  • Side overlap: Between adjacent flight lines (usually 30–40%)

4. Scale

The ratio of the photo size to real-world size. Example: A 1:10,000 scale photo means 1 cm on the photo = 10,000 cm (100 m) on the ground.

5. Ground Control Points (GCPs)

Known points on the ground used to correct and align the image accurately.

6. Digital Elevation Model (DEM)

A 3D map of land elevations, often created using photogrammetry.

7. Orthophoto

A photo that has been corrected for tilt, scale, and relief—so it can be used like a map.

How Does Photogrammetry Work?

  1. Capture:

    • Take multiple photos from different angles (usually using drones, planes, or satellites).

  2. Process:

    • Use software to find matching points between images.

    • Generate 3D points (point cloud) from photo overlaps.

    • Create a 3D surface or model of the area.

  3. Output:

    • 2D maps

    • 3D models

    • Elevation data

    • Orthophotos

Types of Photogrammetry

TypeDescriptionUsed For
AerialTaken from planes/dronesMapping large areas, topography
TerrestrialTaken from the groundArchitecture, archaeology
Close-rangeSmall objects with handheld camerasEngineering, medical imaging

Applications of Photogrammetry

  • Urban planning and mapping

  • Forestry and agriculture

  • Disaster management (flood/landslide mapping)

  • Construction and 3D modeling

  • Heritage preservation (3D models of monuments)

Comments

Post a Comment

Popular posts from this blog

Accuracy Assessment

Accuracy assessment is the process of checking how correct your classified satellite image is . 👉 After supervised classification, the satellite image is divided into classes like: Water Forest Agriculture Built-up land Barren land But classification is done using computer algorithms, so some areas may be wrongly classified . 👉 Accuracy assessment helps to answer this question: ✔ "How much of my classified map is correct compared to real ground conditions?"  Goal The main goal is to: Measure reliability of classified maps Identify classification errors Improve classification results Provide scientific validity to research 👉 Without accuracy assessment, a classified map is not considered scientifically reliable . Reference Data (Ground Truth Data) Reference data is real-world information used to check classification accuracy. It can be collected from: ✔ Field survey using GPS ✔ High-resolution satellite images (Google Earth etc.) ✔ Existing maps or survey reports 🧭 Exampl...
Post a Comment
Read more

Change Detection

Change detection is the process of finding differences on the Earth's surface over time by comparing satellite images of the same area taken on different dates . After supervised classification , two classified maps (e.g., Year-1 and Year-2) are compared to identify land use / land cover changes .  Goal To detect where , what , and how much change has occurred To monitor urban growth, deforestation, floods, agriculture, etc.  Basic Concept Forest → Forest = No change Forest → Urban = Change detected Key Terminologies Multi-temporal images : Images of the same area at different times Post-classification comparison : Comparing two classified maps Change matrix : Table showing class-to-class change Change / No-change : Whether land cover remains same or different Main Methods Post-classification comparison – Most common and easy Image differencing – Subtract pixel values Image ratioing – Divide pixel values Deep learning methods – Advanced AI-based detection Examples Agricult...
Post a Comment
Read more

Development and scope of Environmental Geography and Recent concepts in environmental Geography

Environmental Geography studies the relationship between humans and nature in a spatial (place-based) way. It combines Physical Geography (natural processes) and Human Geography (human activities). A. Early Stage 🔹 Environmental Determinism Concept: Nature controls human life. Meaning: Climate, landforms, and soil decide how people live. Example: People in deserts (like Sahara Desert) live differently from people in fertile river valleys. 🔹 Possibilism Concept: Humans can modify nature. Meaning: Environment gives options, but humans make choices. Example: In dry areas like Rajasthan, people use irrigation to grow crops. 👉 In this stage, geography was mostly descriptive (explaining what exists). B. Evolution Stage (Mid-20th Century) Environmental problems increased due to: Industrialization Urbanization Deforestation Pollution Geographers started studying: Environmental degradation Resource management Human impact on ecosystems The field became analytical and problem-solving...
Post a Comment
Read more

Geographic phenomena fields objects boundaries.

In geography, geographic phenomena refer to features or processes that can be observed and studied on Earth's surface. These phenomena can be classified into three main categories: fields , objects , and boundaries . Each category has distinct characteristics, representations, and applications in Geographic Information Systems (GIS). 1. Fields A field represents continuous, spatially varying data where a value is present at every location within the study area. It describes conditions that exist across a geographic area. Characteristics : Continuity : Fields have no discrete boundaries; the data is continuous. Gradual Variability : The values of a field change gradually across space. Representation : Typically modeled using raster data in GIS, where a grid structure assigns a value (e.g., temperature or elevation) to each cell. Examples : Temperature Map : Shows temperature variation across a region. Rainfall Distribution : Displays rainfall levels over a large g...
Post a Comment
Read more

Landsat 8 Band designation and Band Combination.

Landsat 8 Band designation and Band Combination.  Landsat 8-9 Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) Bands Wavelength (micrometers) Resolution (meters) Band 1 - Coastal aerosol 0.43-0.45 30 Band 2 - Blue 0.45-0.51 30 Band 3 - Green 0.53-0.59 30 Band 4 - Red 0.64-0.67 30 Band 5 - Near Infrared (NIR) 0.85-0.88 30 Band 6 - SWIR 1 1.57-1.65 30 Band 7 - SWIR 2 2.11-2.29 30 Band 8 - Panchromatic 0.50-0.68 15 Band 9 - Cirrus 1.36-1.38 30 Band 10 - Thermal Infrared (TIRS) 1 10.6-11.19 100 Band 11 - Thermal Infrared (TIRS) 2 11.50-12.51 100 Vineesh V Assistant Professor of Geography, Directorate of Education, Government of Kerala. https://www.facebook.com/Applied.Geography http://geogisgeo.blogspot.com
1 comment
Read more