augmented reality - Create an application to measure an object from a photo -

i trying devise way of creating application can measure object in photo - automatically. far, have come across following systems:

• augmented reality
• trigonometry + phone sensors (gyroscope)
• known scale item in photo (credit card, etc.)

however, have couple of questions.

1) of these methods efficient, large batches?

2) how can automate process - i.e. how camera or software detect object going measured (will same, i.e. leaf), measure according either augmented reality marker, scale in photo (credit card), or trig?

any input appreciated.

if want detect particular object automatically (always same object i.e. stop sign) there object detection algorithms works adequately. nice example scale invariant feature transform algorithm (sift)

http://docs.opencv.org/trunk/doc/py_tutorials/py_feature2d/py_sift_intro/py_sift_intro.html

but have problem of photo scale typically cannot calculated single image if want high acuraccy results. can though through stereo pairs of know geometry.

ive written 2 articles bit ago

http://codentonic.net/2013/06/08/camera-simulation/

http://codentonic.net/2013/06/27/camera-ray-reconstruction/

that outline few things relative problem

in general can try combination of creating depth map , finding object feature detection algorithm. far concerns scale can either set markers around object known coordinates (it depth map process well).

generally not easy task.