Accuracy of Ariel Photography?
Accuracy of Ariel Photography?
(OP)
What is the best accuracy available with ariel photography of rural areas and how does it compare with traditional surveying techniques? Can ariel and traditional be readily merged?





RE: Accuracy of Ariel Photography?
In a nutshell though one can get mapping done to around 0.1m with proper techniques. There is a technique which converts aerial photos to a proper map called Orthophotos.
We can obtain 1/10000 scale orthophotos which will allow scaling directly off the map to around 1m accuracy.
Generally it will be more accurate to use traditional ground survey methods as long as the site is not too large. If however vast tracks of land need to be mapped it will probably be more efficient to use aerial mapping techniques.
Lately satellite remote sensing data is also available and approaching accuracies mentioned earlier.
You could probably obtain specific data of accuracies available in your area by contacting your government mapping agency or your local Land Surveyor, or photogrammetry association.
RE: Accuracy of Ariel Photography?
RE: Accuracy of Ariel Photography?
Our company has been using for the past 2 years a high accuracy GPS system (+- 10mm) for rural applications. This system is vehicle mounted and can be used at a travel speed of up to 25km/hr with reasonable accuracy (+- 25mm) which is generally better than required by the client. This accuracy is for both horizontal and vertical position.
This is far more cost effective than aerial photography due to time savings and cheaper equipment utilised.
One of our client has obtained the photographs and the GPS obtained contours and combined the 2 in CAD with a reasonable overlay result.
sc
RE: Accuracy of Ariel Photography?
Sounds quite interesting what you are doing but I would be more interested in knowing which GPS you are using and in what mode - Heights on a moving vehicle - how accurate are these if vehicle bounces? Are you using two receivers (one being stationary) Your results may possibly be adequate for the type of work you do but I doubt if you can be sure of getting 25mm accuracy - yes maybe between successive points but how well do those compare with other points say 2km apart - Before I say any further please elaborate a bit more on how you use the GPS receivers and data processing
RE: Accuracy of Ariel Photography?
Depending on the terrain and visibility of the GPS constellation, 2km spans should be quite doable.
TTFN
RE: Accuracy of Ariel Photography?
The point I am trying to make is that the survey methodology must be designed to befit the accuracy for which the job is necessary. In general I thus agree with what you are doing but be aware of the pitfalls.
Regards
RE: Accuracy of Ariel Photography?
RE: Accuracy of Ariel Photography?
TTFN
RE: Accuracy of Ariel Photography?
http://mapping.usgs.gov/internal/af/Admin/Policy/92nmd10.html
They used these typically 1m pixel resolution aerials to create their digital line maps. Therefore the aerials have to be within 33.3 feet on a 1:12000 scaled map, or 1/30" on a paper map.
More accurate aerials can be produced based on a higher resolution. Houston has 0.5m pixel aerials set to the same DOQQ process as USGS. Therefore they are 4 times as accurate with the higher resolution. Plus when the aerials were flown inassociation with a LIDAR run. Right now LIDAR is taking about 40000 data points per second.