# [talk-au] answers to difficult questions

Arie Paap wildmyron at gmail.com
Mon Feb 22 03:28:53 GMT 2010

```On Sat, Feb 20, 2010 at 2:01 AM, John Smith <deltafoxtrot256 at gmail.com> wrote:
> On 20 February 2010 00:05, Nick Hocking <nick.hocking at gmail.com> wrote:
>> 1)  compass,gps, high school maths.
>> 2) theodalite, professional gps and a real live surveyor.
>> 4) laser rangefinder + gps
>
> These are all the same method, just slightly different tools... and #4
> still needs a direction/compass...
>

The laser range finder + gps method is quite different from compass +
gps / other surveying methods. Instead of drawing lines from measured
gps points according to measured compass bearing and finding the
intersection point, draw circles with radius of measured distance
around the measured gps points and find their intersection.

>> 3) photographic techniques
>> 5) audio tracking ???
>
> How would either of these methods help?
>

Disclaimer: I'm not sure of the practicality of the following ideas
but I think they are interesting.

Photographic techniques: you can use photographic images in place of
compass bearings with some calibration for the field of view. You need
to be able to take photos of several distinct landmarks with known
positions and then it would be possible to correlate the angle of view
between two objects in an image with the number of pixels between
them. Then you can take images of the wind farm (for instance) from
several different locations, determine the angle of view between pairs
of towers from these different locations and from there calculate
their position. There are a few potential problems with this scheme:
a) each object needs to be correctly identified in each image, a
version of "correspondence problem" in machine vision (and this could
be tricky when you have a dozen or more objects of nearly identical
appearance) and b) the lens settings need to be consistent between all
the images which probably requires manual control of camera settings
and is easier with a fixed focal length lens.

Anyway, I think you could make this work, but I'm sure a compass would
be simpler and more efficient.

Arie.

```