- By Survey
it is relatively easy. Your measurements will be in 3 dimensions, X, Y & Z but
ASRix
in spite of
producing a 2D result will accept such measurements. Use the
point list
to identify the
Origin,
Horizontal axis and
Vertical axis
of your coordinate system. This is discussed in more detail in the section
3D coordinates.
Check the
deviation from the 2D plane (the
Z-deviation
column in the
point list
window)
of the other points to make sure everything is, at least, close to being on that plane.
Then rectify as usual.
If the image is not rotated as you would wish it you can use the rotation options of the
output parameters
dialogue box, or draw a Base Line in the
Rectified Image Window
to straighten it out.
(right-click for a menu)
If you get a mirror image it is because you have incorrectly defined the
direction of the Horizontal axis (probably swaping
Origin,
Horizontal will fix it) or you can select one of the
mirror
options from the
output parameters
dialogue box.
- Hand Measurements
are another problem entirely. Here you will, in all probability, be using a 2 dimensional
measurement system and the challenge is to establish a plane surface and the two
axises at right angles to each other.
- On the ground
this can be accomplished with stakes and strings and the 3-4-5 method
(The sum of the squares of the sides equals the square of the hypotenuse -
Pythagoras)
- For vertical surfaces
a plumb bob and a string or water level will help a lot. Use these lines as your axises
and measure
identifiable points relative to them.
- Grids and Scales
Two, visibly calibrated, plumb lines aligned with a level and placed a known
distance apart can provide identifiable points for the rectifier without the need for
further measurements. An example of this approach is described in the
TAPES
example in the samples.
For small objects, such as an archaeological square or a wall or floor detail, a
grid can be placed over the area of interest. If a tripod mounted camera is used
multiple photographs can be taken (with and without the grid device) and the point
file from the example with the grid can be used to rectify the photographs without the
device using the
alternate point file
feature.
- Archival Photos,
even of damaged or destroyed buildings, may provide useful results by measuring
artifacts such as foundations, windows and doors, etc. Metric data can even bee
gleaned from the photograph itself, such as, counting the bricks (especially if you
actually have one to measure) and assumptions about the height of a person, a step or
a door can help, and should not be ignored, when you have nothing else.
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