Topic:
2D navigation off from where it should be.

Description:
When loading 2D station locations, better known as navigation data or shotpoint 
locations, IESX will look at how `straight' the line is and try to generalize or
 filter out unneccessary points.  This is done to cut down on the number of poin
ts which have to be read each time the basemap or seismic is displayed which inc
reases the speed of the display. 
 
How the filter works:
 
-The shotpoints which are loaded either when loading the navigation data from se
ismic trace headers or from a seperate naviagtion data file, are stored in the 2
D locations menu at the same shotpoint interval at which they were loaded.
 
-The first shotpoint that is loaded will be stored in the database. The second s
hotpoint will also be loaded irrespective of the shotpoint increment between the
 two. A straight line will be drawn between the first and second points and betw
een the second and third points and if the angle is less than 0.5 degrees the th
ird point will not be stored in the database. The process then moves along to th
e fourth point which compares the angle between the fourth and third points and 
the third and second points. Thus for  fairly straight lines or lines which grad
ually bend, the only points that may be loaded in the database are the first and
 second and the last points which were in the input file.
  
-What is stored in the 2D locations menu is what was input and not what is store
d in the database.  The locations stored in the database are what determine wher
e the line is plotted on the basemap or how the navigation reads on the seismic 
display.

Solution:
It is not neccessary to have navigation data defined at every single shotpoint
and in fact it would be best to have shotpoints only at the major inflection
points and the beginning and end of the line.

Or can upgrade 10p1 to 10p2 and use IESX 10p2 IESX_UTIL  > 72. 2D General data
manager > 11 - Change tolerance. Please see FAQ on  "What does Option #72: 2D
General datamanager do?" on procedure and explanation.


 




Last Modified on: 21-AUG-98