[OSGeo-Discuss] Finding position based on horizon profile?

[Stephen Woodbridge]

Ok, after thinking about this a little and doing some more googling 
about. It is hard to find the right terms for this question. Anyway this 
is one approach that I thought of.

Given that you had a constrained area - what ever that might be.
You might generate horizon profiles of the area based on prominent peaks 
or features, by viewing those areas from outside the area of interest. 
The goal being to generate wireframe profiles of the ridges and 
mountains in say N-degree steps about the prominent feature. These would 
all get stored for future reference.

Now given a photograph, identify the horizon and any other significant 
terrain features as wire frames.

Now try to match these against the sample references created above. This 
will need to be done very approximately like just matching peaks and 
allowing for horizontal spread based on point of view distance and 
relative height differences from the reference perspective and the 
camera perspective. The idea here is to narrow the field of possible 
perspective images from 1000's to 100's.

This matching might be achieved by doing a linear regression that can 
only distort your image profiles by stretching/compressing the image 
horizontally and/or vertically and computing a least square fit against 
the reference. You would want to keep the images centers aligned 
right-left because you are trying to fine the reference image the best 
aligns with your image because this will give you the heading onto which 
you can then dos more detailed analysis. You can slide the images 
up-down relative to one another. Or try to analyze matching prominent 
features in the profile that match right-left from center.

Then a detailed analysis of this smaller number of possible viewing 
angles and be analyzed. If you can uniquely identify 2-3 features, then 
it should be possible to analyze the distance between them and their 
relative heights and widths to compute heading, distance and azimuth of 
the camera that you could then try to place more accurately on your DEM.

Anyway, having never done anything like this, this would be how I would 
approach it without additional research to direct me in another direction.

-Steve

On 3/28/2011 5:27 PM, Michael P. Gerlek wrote:
> Well, yes, I did do that first and have some angles on the more conventional
> aspects of this, e.g. missile guidance.  Being new to this area, though, I
> thought I'd put out a query to see what else might turn up in the open
> source realm (pure R&D being one thing; hackable code is something quite
> different sometimes).
>
> [that said, sometimes it's hard to even frame the right questions when one
> is in a brand new area..]
>
> -mpg
>
>
>> -----Original Message-----
>> From: Stephen Woodbridge [mailto:woodbri at swoodbridge.com]
>> Sent: Monday, March 28, 2011 2:16 PM
>> To: mpg at flaxen.com; OSGeo Discussions
>> Subject: Re: [OSGeo-Discuss] Finding position based on horizon profile?
>>
>> On 3/28/2011 4:48 PM, Michael P. Gerlek wrote:
>>> Consider the following hypothetical problem:
>>>
>>> Assume we have a good elevation data set for a large region of the
>>> earth -- say, an entire mountain range.  Now let's say we have a
>>> photograph taken from the ground, the horizon of which shows the
>>> profile of a couple of the mountains in that range.  Can you tell me
>>> where the photograph was taken from?
>>>
>>> Any pointers to research in this area would be appreciated.
>>
>> Micheal,
>>
>> Does this help?
>> http://www.google.com/#q=matching++"terrain+profile"
>>
>> -Steve
>