Aerial Photogrammetry is the science of taking measurements from photographs and it relies on a series of images to create an accurate 3D model.
It can be useful as a surveying tool when objects to be measured are inaccessible and when it is not certain at the time of recording, what dimensions are required. The principles of photogrammetry have been known for centuries and it has been used in surveying successfully since the mid-1800s.
An orthophoto is a photograph created using photogrammetry and is one that has been corrected geometrically so that there is no perspective and the scale is uniform across the image. It can be used in the same manner as a map in that true distances between features can be measured. The detail on an image or a 3D model can be plotted to create a 2D or 3D line drawing that can be used in CAD software.
Aerial photogrammetry is an extension of the subject of aerial photography and it allows the rapid gathering of geospatialand visual data when compared with more traditional survey techniques. It would complement rather than replace the more common methods of gathering data such as topographical surveying though it has some specific outputs. It can be used in a number of applications such as architecture, mapping, flood modelling etc. especially where access is difficult, unsafe or impractical.
Below are examples of products created using aerial imagery.
1. A photomosaic generated by photogrammetry. The area surveyed is some 340 x 220m. The profile and volume are generated via photogrammetry and GIS software. As with all products shown below this image is georeferenced for use in CAD or GIS software.
2. Contours generated by photogrammetry software. The formats are CAD and GIS compatible.
3. A colour representation of the digital surface model. The model can be generated in CAD and GIS formats, such as a raster image, shp, xyz, csv files etc.
4 . A simple diagram with arrows showing the direction of flow. The larger the arrows the steeper the fall.
5. Hillshade. Simulates sunlight from a given height and direction.
6. Slope intensity. Horizontal – black. 21° (the maximum slope angle encountered on this image) – white. Shades of grey – 0° to 21°.
7. Section of the survey showing generated spot heights from photogrammetry data. In trials the difference between generated heights and those measured on hard surfaces with survey level GPS instruments has been as little as 13mm.
OTHER EXAMPLES & 3D MODELLING ....
3D MODELS ...
Screen Photography has a partnership with an RICS Chartered Surveyor offering accurate Aerial Surveying and Photogrammetry Services.
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