# How to calculate oblique photo scale?

Is it possible to calculate oblique photo scale by given vertical photo scale ? I mean is there any kind formula relation between them or maybe is it possible to calculate rough approximation of oblique scale ?

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What do you need that for? Is it for aerial images? In that case, you should look for information related to the keywords "orthophotography" and "photogrammetry". – julien Oct 10 '11 at 15:29
Thanks for replay. I am working on software which has to handle described situation. I do not work with aerial photographs, but it could be viewed this way. For example I have aerial images taken by camera whose optical axis is perpendicular to the ground and images taken by oblique camera. For the first case it is easy to find scale, but how to approximate scale for oblique camera? – deephace Oct 10 '11 at 15:46
Do you have access to tools that perform orthorectification? – Kirk Kuykendall Oct 10 '11 at 16:39
What data do you have? Distance to center of photo? Angle of the point of view? You don't need much, because the scale in such photos varies, implying that a decent approximation of the scale near the center will be fine. – whuber Oct 10 '11 at 17:27
Thanks for replays. Sorry I am being dumb. I have all information about camera: focal length (f), angle of view, the height of the camera above the ground (H), etc. I know if camera is vertically positioned then photo scale is f/H. But if camera is oblique then scale varies. It would be great for me if I could approximate such scale with information about the distance from the camera position to the point on the ground whose photo scale is searched. It is not enough for me approximate whole image scale with one value. – deephace Oct 10 '11 at 20:04

Using GRASS GIS (OSGEO)

Ortho-rectification of oblique photographs

In projected location:

``````get approximate camera position:

d.where/d.what.rast:
EAST:             NORTH:
664194.71461534   5104463.03343466

height: 450

Pitch: 20
Roll: 0
Yaw (against north): -45
``````

http://grass.osgeo.org/wiki/Orthorectification_digital_camera#Ortho-rectification_of_oblique_photographs

GIS GRASS http://grass.osgeo.org/

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