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Contouring tool is not showing expected contour lines, the smallest contour lines are missing.

Joe McPherson
  • Updated

Symptom:

Contouring a grid does not result in contours around small areas enclosed by the exact level specified in the contouring parameters. Contours seem to be missing. 

Resolution:

Create a copy of the default contour control file.

  1. Go to C:\Program Files\Geosoft\Desktop Applications 9\etc
  2. Copy contour.con
  3. Paste in C:\Users\{{User}}\Documents\Geosoft\Desktop Applications 9\etc

Edit contour.con file to remove the default minimum length:

  1. Open the copy of contour.con in a text editor.
  2. Look for the line with OMINL* and CMIML** (Line 5).
  3. Add 0,0 to the start of that line.

* OMINL = open minimum length = The minimum length that open contours must have in order to be plotted. The default is 10 mm, max 50. Set OMINL=0 to plot all open contours.
**CMINL = closed minimum length = The minimum length that closed contours must have in order to be plotted. The default is 10 mm, max 50. Set CMIML=0 to plot all closed contours.

Setting the CHINL to 0 is actually all you need, but you may want to set OMINL to 0 as well.

Root Cause:

The contour tool makes the assumption that you don't want or care for small contours. As such, Line Cosmetics (line 5 in the con file) is left blank to use defaults. However you can make a copy of the contour file and create your own without the above assumption, that you can then use with the Have control file option.

Notes:

You may find you wish to adjust smoothing options also, once you have first tested the custom contour file. 

Before you can use the cont.con file, you need to setup your other parameters. Please refer to the CONTCON.GX help file for a description of each setting. In the following example the contour parameters used are:

Example:
_contour.mdf /MDF|scale, ufac, x0, y0
0,0,-1,1 /border, lowtic, smooth, suppop, nth
dp=kt150 /pdef, ptick, pxval, pframe, psidel
1.5 /hlb, htl, hcr, htk, hxv, hsl
0,0     /ominl,cminl,skipa,skipb,skipc,skipd,skipe,skipf
0,0, /xval, digxv, minxv, markxv
1,,,0,,,-1 /levopt, conbeg, conend, lbup, lbmult, logopt, labelcol
0,1,C1=kt150,0,0.5,0 /cint,lintyp,catt,label,dense,digits,conlo,conhi

To use the custom contour file:

  1. Map Tools > Contour > Have control file
  2. Select Input grid > Select custom contour file > OK