Question

Aerial photography can be used to produce a variety of map products useful for landscape management and engineering applications.

i. Briefly explain how a Digital Elevation Model (DEM) of a landscape can be generated from overlapping aerial photographs.

ii. What is an orthophoto? How does it differ from an aerial photograph?

iii. A potentially very useful product that can be supplied to landscape managers and engineers is a ‘stereo-model’ that can be viewed, interpreted, and measured using heads-up 3-dimensional viewing technology:

a. Explain how two images can be displayed on a computer screen and visualised in 3-dimensions?

b. What advantages might this technology offer a practising land manager or engineer?

Answer 1

Ans(i) : Digital Elevation Model is a type of 3-D model which is used for representing surface of any terrain which would include any planet, moon or any asteroid in the universe. It is being created by the elevation data in the terrain. If it is written as globally DEM then it is the global model of elevation. The main thing behind this model is that we have to obtain the elevation of any surface and that is possible by one methodology. Different aerial photographs are being taken of the surface and those which are more elevated are marked as relatively darker and then what we have to do is super imposing of several aerial photographs and hence the main set of photograph is being formed and we get the elevated height of all the points on the surface and the digital elevation model of that terrain is being created.

Ans(ii) : An orthophotograph is an ortho image of the aerial photography in such a way that all scales are being maintained. It is different from the aerial photograph because that is the satellite image and scales are not being maintained in that and it's a bit difficult to trace out the original location where as ortho photograph is an advanced and better version on the location point of view or aerial photographs.

Ans(iii) : A stereo model is the overlapping of different photographs with different image identifiers in such a way that the image IDs comprise of each pairs. It is used to view any pair of image in 3-D.

a) The technology of stereo model can be used to visualise any given pair in 3-D in computers. Different aerial photographs are being super imposed on each other and by that the elevation and the plan view are being obtained and After that stereo model helps to correlate the pair of images and we'll be able to obtain the display and visualise the Pair in 3-D.

b) Below are some advantage of this technology used

• Ability to view any available scene in 3-D
• Identification of features that may exist in the scene.
• Multi angle view is available to the audience