science

Orthophoto

Orthophoto is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Orthophoto rather than just read about it. In short: An orthophoto, orthophotograph, orthoimage or orthoimagery is an aerial photograph or satellite imagery geometrically corrected ("orthorectified") such that the scale is uniform: the photo or image follows a given map projection. Unlike an uncorrected aerial photograph, an orthophoto can be used to measure true distances, because it is an accurate representation of the Earth's surface, having been adjusted for topog…

Key takeaways

Orthophoto belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Orthophoto to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Orthophoto from memory before moving on to harder problems.

Reference excerpt

An orthophoto, orthophotograph, orthoimage or orthoimagery is an aerial photograph or satellite imagery geometrically corrected ("orthorectified") such that the scale is uniform: the photo or image follows a given map projection. Unlike an uncorrected aerial photograph, an orthophoto can be used to measure true distances, because it is an accurate representation of the Earth's surface, having been adjusted for topographic relief, lens distortion, and camera tilt. Orthophotographs are commonly used in geographic information systems (GIS) as a "map accurate" background image. An orthorectified image differs from rubber sheeted rectifications as the latter may accurately locate a number of points on each image but stretch the area between so scale may not be uniform across the image. A digital elevation model (DEM) or topographic map is required to create an orthophoto, as distortions in the image due to the varying distance between the camera/sensor and different points on the ground need to be corrected. An orthoimage and a "rubber sheeted" image can both be said to have been georeferenced; however, the overall accuracy of the rectification varies. Software can display the orthophoto and allow an operator to digitize or place linework, text annotations or geographic symbols (such as hospitals, schools, and fire stations). Some software can process the orthophoto and produce the linework automatically. Production of orthophotos was historically achieved using opto-mechanical devices. The orthorectification is not always perfect and has side effects especially for the geometry of high-rise constructions. When using the top-most digital surface model (DSM), instead of the bottom DTM, the resulting product is called a true orthophoto.

Orthophotomosaic and orthophotomap

An orthophotomosaic is a raster image mosaic made by merging or stitching orthophotos. The aerial or satellite photographs have been transformed to correct for perspective so that they appear to have been taken from vertically above at an infinite distance. Google Earth images are of this type.

The document (digital or paper) representing an orthophotomosaic with additional marginal information like a title, north arrow, scale bar and cartographical information is called an orthophotomap or image map. Often these maps show additional point, line or polygon layers (like a traditional map) on top of the orthophotomosaic. A similar document, mostly used for disaster relief, is called a spatiomap.

See also Digital orthophoto quadrangle (DOQ) and digital orthophoto quarter quadrangle (DOQQ) GRASS GIS (i.ortho.photo module) IMAGINE Photogrammetry, formerly Leica Photogrammetry Suite Photogrammetry Photomapping Rational polynomial coefficient SOCET SET TopoFlight United States Geological Survey

References

Further reading Bolstad, P., (2005), GIS Fundamentals: A First Text on Geographic Information Systems, Eider Press, White Bear Lake, MN, 2nd ed. Demers, Michael N., (1997). Fundamentals of Geographic Information Systems, John Wiley & Sons. Fernandez, E.; Garfinkel, R.; Arbiol, R. (May–June 1998). "Mosaicking of Aerial Photographic Maps Via Seams Defined by Bottleneck Shortest Paths". Operations Research. 46 (3): 293–304. doi:10.1287/opre.46.3.293.. Petrie, G., (1977), Transactions of the Institute of British Geographers: Orthophotomaps New Series, vol. 2, no.1, Contemporary Cartography., pg. 49–70 Robinson, A.H., Morrison, J.L., Muehrcke, P.C., Kimerling, A.J., Stephen Guptill, (1995) Elements of Cartography: John Wiley & Sons Inc., Canada, 6th ed. United States Geological Survey, US Department of Interior, USGS Fact Sheet May 2001 https://erg.usgs.gov/isb/pubs/factsheets/fs05701.html Archived 2008-06-02 at the Wayback Machine

External links United States Geological Survey National Digital Orthophoto Programs (NDOP) – original site via Wayback Machine National Digital Orthoimagery Program (NDOP) Archived 2017-10-11 at the Wayback Machine National Digital Orthoimagery Program Subcommittee

Illustrations

Orthophoto: This photo is properly projected on elevation model, yet on a single building scale, a small tilt is noticeable. This is an orthophoto, but not a true orthophoto (not all vertical features are reprojected). — This photo is properly projected on elevation model, yet on a single building scale, a small tilt is noticeable. This is an orthophoto, but not a true orthophoto (not all vertical features are reprojected).

Orthophoto: This photo is assembled from several overlapping photos from UAV, completely removing any residual tilt of the buildings. This is a true orthophoto. — This photo is assembled from several overlapping photos from UAV, completely removing any residual tilt of the buildings. This is a true orthophoto.

Worked examples

Example 1 — a first encounter with Orthophoto

Start with the simplest possible case. Write down what Orthophoto claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Orthophoto before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Orthophoto ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Orthophoto

In research: Orthophoto appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Orthophoto in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Orthophoto is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cartography, Photogrammetry, Remote sensing, so understanding it makes those chapters shorter.
In everyday life: Look for Orthophoto outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Orthophoto in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Orthophoto means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Orthophoto out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Orthophoto in simple terms?

Why does Orthophoto matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Orthophoto?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Orthophoto.