Hi David,
To calculate speed I would suggest the following.
Run the Utility/Make distance channel Gx to create a distance channel. This
will be the cumulative distance down a line.
Use the X-Utility/Filters/Convolution filter gx with a coefficients of 1,-1
to create a new channel of the distances between adjacent points.
Use the convolution filter again with the same filter coefficients on the
time channel to obtain the time difference between adjacent points. A simple
math formula will then yield the speed.
Note, that as the convolution filter has an even length the position of the
result is halfway between the points, i.e. offset by half of a fiducial. If
this is an issue, you can apply a lag correction to the result.
Alternatively you may use a three point coefficient for the filter,say
1,0,-1, so that the result will not be offset, although then you are looking
at n-2 which may not be what you desire.
Louis Racic
Manager Technical Solutions
Geosoft
-----Original Message-----
From: David Humphrey [mailto:[EMAIL PROTECTED]]
Sent: July 15, 1999 3:42 PM
To: '[EMAIL PROTECTED]'
Subject: [geonet]: Calculating speed from (x,y,t) points
I have a database containing (x,y) coordinates and time for each point. I
want to calculate speed s at each point according to the formula:
S2 = (d2-d1)/(t2-t1)
Where d1 and d2 are the distance along the line for successive points. I
see a GX that does the distance calculation, but don't see how to get the
time difference. The problem is using values from different records in a
.gdb.
I know I can write a GX that does this, but would like to use existing Oasis
montaj machinery, if possible. Does anyone know a better way?
Thanks in advance.
David L. Humphrey
Manager, Software Development
Bell Geospace, Inc
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