Topic:
Why is the aspect ratio/scaling for the timeslice incorrect?

Description:
My 3D survey has rectangular bins. However, the bin aspect ratio appears
to be square when displaying time slices at some scales.
What causes this?

Solution:
The time slice aspect ratio/distance scale is not exact since monitor 
display resolution is limited to about 100 pixels per inch and each data 
point (sample) must be represented using an integer number of pixels in 
both the x and y directions. Note that at large scales multiple bins may 
be represented as a single sample.

Consider as an example a crossline spacing of 50 feet and an inline spacing 
of 100 feet.  A scale of 25 feet per pixel would produce a time slice 
display in which each bin would be 4 pixels by 2 pixels so the aspect
ratio would be correct.

A problem arises for the 50x100 foot bin when a scale of 20 feet per 
pixel is chosen. Keeping in mind that each sample must be represented by 
an integer number of pixels, the bin can be represented as 5x2 pixels or 
5x3 pixels, neither of which results in an accurate aspect ratio. Seis3DV 
will settle on an inline scale which is nearest to the selected
scale. Hence the unexpected scales/aspect ratio.

In practice, we specify the scales as traces-per-inch or distance ratio.  
So if we choose a distance ratio of 1:24000 we are trying to display 2000 
feet of data in an inch on the monitor (about 100 pixels).




Last Modified on: 07-APR-00