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Perspectives Header

Both GPS and aerial-satellite sen­sors are used to gen­er­ate data suit­able for cre­at­ing a dig­i­tal ter­rain model (DTM). In the case of GPS, a series of points are mea­sured through tri­an­gu­lat­ing sig­nals orig­i­nat­ing from a series of GPS satel­lites. Alter­na­tively, aerial-satellite plat­forms that include sen­sors, such Lidar, radar or even using pho­togram­me­try tech­niques may also be used to gen­er­ate a DTM. When is it bet­ter to gen­er­ate a DTM from GPS tech­nolo­gies as com­pared to aer­ial or satel­lite sensing?

Many peo­ple depend upon a dig­i­tal ter­rain model for a num­ber of dif­fer­ent rea­sons. Ele­va­tion mea­sure­ment of the earth’s sur­face is an inte­gral piece of infor­ma­tion. Flood map­ping depends upon cor­rect ele­va­tion data. It helps us to under­stand where ris­ing water lev­els will appear and pro­vides valu­able infor­ma­tion for emer­gency plan­ning and response. Know­ing the ele­va­tion sup­ports deter­mi­na­tion of aspect (north-south-east-west) of a given point, thus know­ing where the sun will shine or not, the wind will occur mostly, as well as the suit­abil­ity of a par­tic­u­lar land use — par­tic­u­larly for agri­cul­tural, con­struc­tion or trans­port. Obvi­ously trains can­not run up or down fifty degree slopes, for example.

Tra­di­tion­ally ele­va­tion has been mea­sured by run­ning  a tra­verse across the land, care­fully cal­cu­lat­ing ele­va­tion of a series of each point rel­a­tive to known bench­mark ele­va­tions. By tying these tra­verse points to well-known sur­vey con­trol points whose ele­va­tion is known, a coor­di­nated sys­tem could be cal­cu­lated with both newly acquired sur­vey data in addi­tion to already exist­ing measurements.

The same prin­ci­ple applies to aer­ial sens­ing for pho­togram­me­try pur­poses whereby flight plan­ning often entails deter­min­ing flight lines (where the air­craft will fly) to avoid exces­sive over­lap (side­lap, end­lap) and boundaries.

Thus flight lines are inter­preted sim­i­larly to ground tran­sect lines with infor­ma­tion gath­ered along them using either GPS on the ground or aer­ial cam­eras from an air­plane — two dif­fer­ent tech­niques and approaches.

On the other hand, satel­lite In the case of GPS, advanced tech­niques are often used and this may include GPS net­works. For exam­ple, the Ord­nance Sur­vey in the UK oper­ates a GPS net­work across the coun­try — as do many other coun­tries. The results of mea­sure­ments using GPS tech­niques can often be bet­ter than half a meter and may approach cen­time­ters in most cases. This is also true for aer­ial gath­ered data using dig­i­tal pho­togram­me­try tech­niques. Satel­lite sen­sors can also acquire ele­va­tion data with a high level of accu­racy and precision.

But can we sep­a­rate one tech­nol­ogy from another for a given appli­ca­tion? For national or broad regional ques­tions that demand sim­i­lar data across long dis­tances, it is often imprac­ti­cal to start build­ing a grid­ded net­work of GPS points. If the points are widely sep­a­rated, then the derived ter­rain model may not rep­re­sent undu­la­tions and changes occur­ring between mea­sured points accurately.

Con­versely, aer­ial or satel­lite gen­er­ated DTM infor­ma­tion may include costs that are pro­hib­i­tive to their use, par­tic­u­larly for small and inter­me­di­ate sized com­pa­nies. I have heard this stated many times.

But the fact is, peo­ple do not use DTM’s alone. They are usu­ally cou­pling them to other goals and pur­poses asso­ci­ated in their projects. It is not uncom­mon to see other sen­sors, often expen­sive and demand­ing a high degree of knowl­edge for their oper­a­tion and can be used together with topog­ra­phy. In some instances sen­sors that mea­sure radi­ance, salin­ity, aerosols, traf­fic and other appli­ca­tion types may include spa­tial pro­cess­ing that is depen­dent upon topography.

Did you know that about 18% of top US farm pro­duc­ers are pro­duc­ing about 72% of that coun­tries corn? These are the alpha or early adopters in the agri-food pro­duc­tion cycle. While the geospa­tial has at times dis­missed the agri­cul­tural com­mu­nity for more lucra­tive waters, the fact remains, this core group (and they exist around the world), base their deci­sions on sci­ence, knowl­edge and new tools. They achieve effi­cien­cies and aim for them, and they ben­e­fit from the returns.

This group of peo­ple under­stand that food pro­duc­tion is a series of processes, much like con­struct­ing a build­ing, and they cou­ple topog­ra­phy into quite a few of these processes, from seed­ing to man­age­ment to dis­tri­b­u­tion and mar­ket­ing. They are pur­su­ing ‘whole plant sys­tem agri­cul­ture’ that effec­tively ties 3D into the pro­duc­tion cycle as they develop sus­tain­able agri­cul­tural systems.

These sys­tems are com­plex, but the drift towards sim­plic­ity is enabling these changes while main­tain­ing the real com­plex­ity under-the-hood.

This poses unique chal­lenges for the GPS indus­try in agri­cul­ture, since laser remote sens­ing and radar can effec­tively pro­vide a more densely mea­sured topo­graphic net­work. How­ever, the role of GPS is about to change and become more tightly cou­pled to sec­ondary sen­sors and other tech­nolo­gies that sup­port the dig­i­tal farm and whole plant agri­cul­ture in 3D. That 18% or alpha group is lead­ing the way in terms of tech­nol­ogy use and appli­ca­tion. They are found in areas like wines, grains, hay, beans and fruit pro­duc­tion. Their work will lead towards higher trace­abil­ity, greater food secu­rity, more effi­cient processes for pro­duc­tion and include dis­tri­b­u­tion and eco­nomic net­works linked directly to bank­ing and finance.

Is aer­ial sens­ing or GPS more effec­tive for topog­ra­phy appli­ca­tions? In many ways topog­ra­phy is a key ele­ment that will play a major role in the upcom­ing 3D agri­cul­ture future. Imag­ing sen­sors will mon­i­tor pro­duc­tion and also pro­vide valu­able infor­ma­tion. I sus­pect that the sweet spot in all of this will be the point where GPS and topo­graphic tech­nolo­gies con­verge to sup­port agri­cul­tural processes more effec­tively. This is dif­fer­ent than pro­vid­ing tech­nol­ogy alone, it requires an under­stand­ing of how the early adopter agri­cul­tural com­mu­nity really see agri­cul­ture in the future.

While the 3D build­ing envi­ron­ment is pur­su­ing 3D BIM and other appli­ca­tions, an anal­ogy can be drawn, closely, to what farm­ers are think­ing about under­ground in terms of roots and how they gauge land tenure, oper­a­tions, pro­duc­tion and main­te­nance over the sus­tain­abil­ity cycle.

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Jeff Thurston is edi­tor and co-founder of V1 Mag­a­zine. He is based in Berlin.


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