Photogrammetry: how does it work?

This     week     we     will     talk     about     a     very     special     technique:     Photogrammetry.     Automatic     digital photogrammetry   is   a   methodology   that   allows   to   elaborate   a   three-dimensional   model   starting   from digital   photographs.   Personally   I   had   read   of   this   technique   in   some   computer   magazines,   but   I   had never tried to use it. By    doing    research,    I    discovered    that    it    is    a    very    widespread    technology    today,    to    realize    three- dimensional   models   in   various   fields:   topography,   architecture,   archeology,   geology   ,   medicine,   graphics ...   Its   widespread   use   is   due   to   the   fact   that   there   are   specific   low-cost   software,   their   simplicity   of   use and the need for basic equipment consisting of a digital camera and a medium-performance PC. To   test   this   new   way   of   digitizing   a   three-dimensional   object   starting   from   a   series   of   photographs,   I chose to use a small statue printed in 3D, which I found on a shelf in the laboratory. ( FIG.1)   Thanks to those who did it!

Final Test

To   further   verify   the   generated   object,   after   having   saved   it,   I   imported   it   into   the   CURA   3D   Printing   Software,   the   processing   defects   are   very   evident,   I   do not consider it appropriate to proceed with 3D printing.

Folder Selection

(1) The first step is “Add Folder” from “Workflow” menu. The folder contain the 110 pictures of my object.

Camera Creation

(2)   Now   I   can   set   the   data   layout,   select   " Create   camera   from   each   file "and   confirm   the   option   with   the   left   mouse   button   on   the   "OK"   button   on the screen

Photos Alignment

(3)   The   next   step   is   “ Align   Photos ”   from   “ Workflow ”   menù,   Very   simple   to   do,   just   click   the   menu   and   select   the   item,   the   process   is   automatic   and does not require any intervention on our part.

Software: Photoscan 3D modeling and mapping

To experiment with this technique, our course plans to use the Photoscan 3D Software. (FIG.2) After   downloading   and   installing   the   software   with   a   simple   wizard,   we   are   ready   to   get   to work. Obviously we miss the photos!

A small discovery:

Although it may seem like a very modern technique, I've actually discovered that photogrammetry is more than a century old! In   1849   we   have   the   first   example   of   photogrammetry,   ie   analysis   of   photographic   images   for   the   realization   of   topographic   maps.   Afterwards,   the technique   of   aerial   photogrammetry   was   perfected,   especially   made   from   the   top   of   hot   air   balloons,   very   useful   for   military   purposes.   An example of this use can be the Battle of Solferino, in which Napoleon III ordered a reconnaissance to be performed with this technique!

Let's take pictures

To   take   a   considerable   amount   of   photographs,   I   decide   to   place   the   small   statue   on   a   support   (FIG.3),   in   a   convenient   position   in   the   middle   of   the room,   which   allows   me   to   go   around   the   subject.   My   camera   has   the   burst   function   and   then   I   decide   to   use   this   shooting   mode   to   quickly   record   a large amount (FIG.4) of frames to be processed.

How to create our object

Now   that   I   have   the   photos   to   process,   I   launch   the   Software   and   after the   initial   splash   screen   (FIG.5),   I   can   see   the   editor   and   its   various menus and tools. Now   let's   see   how   to   proceed,   step   by   step   to   get   our   digital   object. The   procedure   consists   of   a   series   of   processing   steps   that   must   be performed in the right order, let's see what they are:

Dense Cloud

(4)   From   the   same   menu   “ Workflow ”,   we   can   select   the   “ Build   Dense   Cloud ”   command…At   this   point   there   is   a   good   and   a   bad   news:   the   good thing is that the process is automatic and we do not have to do anything to complete it. The   bad   news   is   that   this   is   the   first   phase   that   takes   a   lot   of   time   to   process   the   data   (FIG.6),   personally,   at   this   point   I   recommend   leaving   the computer alone and going for something else!

Build Mesh

(5) When the processing is finish…the next step is to Build a mesh, to do it I select “ Build Mesh ” Item from “  Workflow  ” menù (FIG.7). At this point a Box opens with multi-selection menus (FIG.8), we must set the values as follows:

Results of Photogrammetry

Finally   we   created   our   3D   object   thanks   to   the   technique   of   photogrammetry.   The   result   is   not   perfect,   there   are   disconnected   polygons.   Surely   it   was interesting   to   experiment   with   this   method   of   digitization   that   allows   you   to   generate   three-dimensional   objects   from   two-dimensional   photos.   Surely, continuing   to   practice   you   can   improve   the   results.Perhaps   a   limitation   of   this   technology   are   photographs,   which   if   they   are   not   done   in   the   right   way, can compromise the final result.