Rest In Peace Topographic Contours - Part 3

Paul Hooykaas
Apr 10, 2013

This is a second of a contribution provided by mineral industry leaders.  Paul Hooykaas, who works as the Product Manager at Micromine, responded to my topography posts by emailing me a historical account of topographic surveying from his experience which I found fascinating and enlightening. I asked him to share his email with our readers as many of the younger generation would be unaware of these details.  So today Paul provides Part 3 of the topographic contour series of posts.
Please note that this is Paul's personal opinion and not that of Micromine. - Jun Cowan

I share your dislike for contour lines as a definition for topography.  I have a land surveying background, so perhaps my reasons for this are slightly different to yours.
To understand contours we need to step back to the previous century.  The year 2000 is quite an appropriate marker for two reasons:

  1. That was when Selective Availability was removed from GPS, allowing it to become a mainstream technology.
  2. Although not as clearly defined, it was also signaled the arrival of affordable 3D graphics (in 1998 a Mac graphics card capable of serious 3D visualisation, cost US$3,000)

The good old days!  Source:

Topographic contours - 20th century representation of topography

It is fair to say that in the 1900s contours “ruled”.  They were clearly the best way to represent topography both on paper (hardcopy) and with 2D graphics (GIS applications). It is also worth reviewing where these contours came from.

  1. Small scale projects often involved a land surveyor doing a selective pickup. By this I mean that the measured points were along ridges, valleys, road edges at changes in slope and extremes in height.  By choosing carefully the surveyor get can get the best result from a minimal data set. The output effectively becomes “smoothed” by hand drawing contours after plotting the spot heights.  Later, computer programs would be capable of generating contours automatically, usually by first creating some type of terrain model.
  2. Large scale mapping was done using aerial photography.  The surveyor was again involved by placing and accurately locating, ground control points.  Photogrammetry involves looking at two overlapping aerial images through a stereoscope. This provides a three-dimensional view of the land.  A stereoplotter uses these photographs to determine elevations. It has been the primary method to plot contour lines since the 1930s  By dialing in a elevation, a dot would appear. The trick would be to move the dot so that it appeared to sit exactly on the ground surface. Tracking that elevation effectively produced a contour line.  In the 1970s I had the opportunity of sitting at a stereoplotter. With this particular model there were two dots that appeared coincident at a particular elevation. The machine had a couple of wheels that controlled the movement of the dots.  The frustration of trying to both move the dots and keep them on top of each other, gave me huge respect for the skill of the experienced operators who zoomed along hill sides with nonchalant ease. 

Stereoplotter.  The two mechanical hand wheels effectively worked as a 'mouse'. Source:

LIDAR and point clouds rule in the 21st century!

Today LIDAR “rules” the mapping world.  Large scale uses fixed wing aircraft while smaller regions use helicopters. In fact helicopter surveys are becoming common practice for many drilling programs in Australia. 
Today’s topographic surveyor is more of a technician.  One man and a (GPS) pole can efficiently handle localised pick-ups.

LIDAR is usually associated with a laser scanning device. The technology can be used to generate very precise 3D models associated with architecture and CAD. 

Essentially what happens is that lots and lots of very accurate measurements are made.  Far more than are necessary to model the result.  The raw data is commonly termed a “point cloud”. The tricky part is isolating the points you want and discarding the rest. In terms of using LIDAR to map topography there will be numerous “false” reflections.  Vegetation, power lines and buildings are obvious examples. A lot of pre-processing is required to both filter out unwanted points, stitch together overlapping scans and then work out how to properly model any remaining “noise”. There is some pretty clever software out there to handle this, and it is getting smarter all the time. 

Transmission line is automatically picked by LIDAR processing software. Source:

This software invariably produces a mesh, or wireframe, representing the surface.  The odd thing is that very often the result is exported as contour lines. . Why? These days very few people actually use contours. All that happens is that they are converted to a Digital Terrain Model (DTM) - which is what LIDAR gives you directly.  Alternatively (if you ask nicely) you can get the raw (or partially processed) point cloud data.

To me this is simply bizarre.  Far more useful would be to output a triangulated surface. Or wait, better still, several versions of the surface, with different triangle resolutions, so that you can choose one that is fit for purpose.

To illustrate why it is best for the LIDAR contractor to provide a surface, rather than a point cloud, consider a bathymetric example (using similar techniques).  An end user might apply the same “topographic” algorithm to model the sea floor. The result would look smooth and realistic. It is only when someone asks “at what stage did you apply the tidal correction?”, that you might reconsider the accuracy of model.

Topography surface from LIDAR is not what you expect

Even topography may not be as simple as it seems.  If you viewed a raw point cloud as 3D dots, by rotating it and looking at it from different angles, it soon becomes obvious that a large number of the dots are on a "lowest plane" and the rest seem to float above it. So perhaps we should be modelling the lowest horizon rather than the middle of “noise”.  This may well depend on how the data was captured.

In any case, the contractor will almost certainly have both the best knowledge and the specialised software to generate an optimum result.  In fact every client should be demanding this output. LIDAR does not come cheap, so the deliverables should be useful. While customers continue to accept contour lines, the geologist will either finish up with second rate surface models or have to do significant post processing themselves.
We are now well into the 21st Century.  Times have changed, and contours should be by-products, not the definition of a digital terrain model. 

Paul Hooykaas


  1. 1 Ramón Aguirre M. 25 Apr
    This is very interesting. I wonder if any of you have historical data like this, but on cross-sections?. Common practices have a kind of inertia that keeps them in use even when a much better alternative is available at a lower cost. It´s like the QWERTY keyboard or that tale about a traditional fish recipe that involves cutting the head and tail, without knowing that the tradition originated from a frying pan that was too small. Likewise, I imagine the first geologists where desperate for a way to represent their models in 3D but had to reluctantly settle for cross sections. Now that there is a way, some modern-day geologists just cannot let cross-sections go. If anyone can share historical data that highlights this irony, it would be much appreciated.
  2. 2 Jun Cowan 29 Apr
    Yes, you make a good point, and I have been thinking about this issue for a while.  Cross-sections are useful but in most situations vertical sections are not true structural cross-sections so these sections are not very useful.  A true cross-section is the plane that is orthogonal to the symmetry plane or axis of the structural fabric being modelled.   I've not come across too many deposits where the drill hole fences are perfectly positioned and one reason for this is because the structural fabric of the deposit has not been worked out by the geologists.   I don't use these vertical sampling planes at all when I model geology or grade, and in fact I think they are the primary reason why geologists misinterpret geology and grade continuity.  I would personally abandon the practice of drilling in vertical fences.    But getting geologists to examine structural geology or abandoning the practice of sectional interpretation will take a long process of education and I will be discussing these topics in future posts.  Meanwhile software companies continue to release products which reinforce the practice of drawing in vertical sections and in plan, without giving any geologically sensible reasons why we should be doing this.  
  3. 3 Tim Elliott 07 Sep
    What dimension am I in? 

    Can I give topographic contours a little CPR? They are still very useful!  I see 2D and 3D mentioned extensively (no 4D?). I see all manner of surfaces on my screen, lots of colours. Lots of shapes. I see discussions of the merits of 2D vs 3D. But here is my question. Where are these dimensions? I saw a coloured topographic surface, I reached into the screen and my fingers just banged into the surface. I could not pick it up. Because its 100% 2D. 

    All these disparate tools are just that. Tools. The dimensions are in the Geologists head. The tools, be it interpolation, triangulation, colour or topographic contours are visualisation aids. Nothing more. Different tools for different jobs. Thus, I agree with some comments in the earlier blog. I think vertical, parallel sections of drilling is a ready made nightmare. The reason I say this is while the product is an object easily visualised in 3D, the creator is actually thinking in almost 1D. The brain is working from section to section perpendicular to the drill fence line. Have you noticed wireframes are almost always perpendicular to the drilling, as if the perfect drilling direction was chosen (as Jun stated) yet this choice is always made before drilling has started, often on very scant information. As stated, its rarely the right direction in my experience as well. 

     A computerised surface lets you visualise the shape of the land extremely well, using rendering and shading. 

    Topographic contours should allow a good geologist to "see" a map in 3D. Its also a 2D representation of data but with proper training you are thinking in 3D. But they have other uses. In,I've a surface, they let me see not just the shape, but the numerical point heights. Their spacing is a mathematical product of the slope of the surface. That's where they become powerful. I can do the exact same thing to a geological surface (a structure contour) and the use of those two contours together has a great many applications. None of the software mentioned has a mobile version. Im a field geologist. I love predictive modelling, and topographic contours, combined with structure contours allow me to perform predictive modelling, in the dense NZ bush, in the rain, while standing on the outcrop, from a measurement or from multiple outcrop points. I can project that structure or contact working in 3D and then I can map the true contact. If they deviate from each other, I have learned something valuable. 

    This is how I work. May I please keep my topographic contours alive just a little longer!
  4. 4 Tim Elliott 07 Sep
    I must apologise if that does not read well. I was typing on an Ipad and could not actually see it as I typed! My dog destroyed my computer, and its a bad industry downturn. But if need be I can still create topographic contours myself, by hand with a compass and a chain (lazer range finder) , and then map onto them and still "work" in 3D, and cut proper sections, in the right orientations, not just the orientation the software can handle. 

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