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Some advises

Some general advises for beginers...

1 - Always brings your computer with you and do the computations on site. Never do the shots on site only and hope it will compute at your factory (a problem like blurred photos is always possible).

2 - Always do a first test with some coded targets before positionning all... Only to see if the size is correct and targets are "readable". Nothing is more frustating than discover the targets are too small after taking one hour to position it !

3 - Do not hesitate to add too much coded targets, even where you think you do not need, just for helping the software to compute (it is not magic, it is mathematic only, the more there are targets, the better it is...). Especially if you plan to use uncoded targets.

4 - Try to dispatch Coded targets equaly on the objet, even if you think you don't need points, again just for helping the software to assemble the scenes.

5 - Uncoded targets are more difficult to get than coded targets. Uncoded targets needs the photos are good... Be sure you are successfull with coded targets before using uncoded.

6 - Always move yourself between two shots. Never takes several shots without moving youself, to see here :
http://www.rhinophoto3d.com/support/faqs/1-general-questions/35-how-to-take-shots-for-photogrammetry.html

7 - Paid a lot of attention to the camera calibration and follows exactly the process  with a good grid  on a perfect flat area (you have to get same photos that the ones in the documentation).

 

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General info on photogrammetry and Cameras

Several potential customers requested information on cameras and how to get accuracy with Rhinophoto...

The camera :

More the sensor is large and the quality of photo is good (no noise, black color is black, white is white...) better is the accuracy and ease of use.
Two examples bellow :
A zoom on photos of a good cameras (Nikon DSLR)
good01.jpggood02.jpg

Some "poor" cameras (Compact camera)
bad01.jpgbad02.jpg
You can understand easily that the accuracy and reconstruction will be less good with the second ones...

The lens used :

A fixed focal lenght gives always better results :  More the lens is simple, better the accuracy is, a zoom lens have a lot of lens and gaps inside.
The best lens for photogrammetry are : fixed 24mm focal length.

The Quality of camera calibration :

The grid have to be perfectly flat and the process have to be exactly like the documentation.

The number of reference bar used :

eg. If you use 3 Reference bar well positionned (eg : two at each ends + one in the middle of the hull) Rhinophoto use these 3 known values to "Conform" the scene, and force the 3 values to be exact, that give the best accuracy.

The number of photos and number of targets :

the more there are targets and photos the better it is. To see the videos
How to Positon Coded Targets  http://www.rhinophoto3d.com/files/videos/Rhinophoto_V3_Training_Position_Targets_en.html
and
How to Take the Shots http://www.rhinophoto3d.com/files/videos/Rhinophoto_V3_Training_How_to_Take_Shots.html

The quality of photos :

if photos are well centered, taken with angle... it increase the accuracy

The sensor resolution :

higher the resultion is, better it is. But, important, it is preferable to have good sensor with lower resolution than hi-resolution with noise and no contrast. eg a Nikon DSLR 12 Megapixels is better than any compact camera 16 Megapixels.

The size of sensor :

the bigger it is, the better it is .
For example we have made several tests with different Nikon DSLR cameras :
- The more accurate is the Nikon D700 + 24mm f2.8D Nikkor lens (a big plus : the large sensor give a wide angle very easy to take shots and get projects) Price ~ 2600/3000€
- Then Nikon D300S + 24mm Nikkor Price : ~1800€
- Then Nikon D7000 + 24 mm Nikkor Price : ~1600€  (Good quality/price ratio, very close to the D300s in Quality of digitizing)
- Then plastic body Nikon DSLRs...  D5000+ 18/55 lens then D3100 + 18/55 lens Price ~500/600€ but lens are less accurate
If possible buy a NON VR lens (VR is Vibration Reduction and move lens inside, not good for photogrammetry, even if this VR feature is de-activated

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New Magnetic Targets

We received our new magnetic targets for steel hull digitizing.

Hi quality CNC cutted magnetic sheet, with codes CNC cutted in Extra matt Adhesive Vinyl

Is available on demand...

magnetic targets.jpg

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A test on Webframes

Webframes digitizing

surfaceswithphoto.jpg
Yesterday, I made a digitizing of Webframes inside a boat in way of refit. My customer have to CNC cut near 500 plates adjusted between the webframes.
These webframes are particulary difficult to measure with conventionnal tools because everything is inclined.

The idea was to use the Rhinophoto module Countertop and modify a bit the code to adapt for Webframes digitizing and drawing. I made some comments in the code to avoid drawing some un-needed area... (ask me the code : support[at]rhinophoto3d.com, if you want to test).

The customer CNC cuts some rules in wood. I glued the countertop targets on the rules.
.rules.jpg

I made 7 pairs of rules with different length (2 pairs 500mm, 3 pairs 700mm, 2 pairs 900mm).
Inside the boat we positionnate the rules by pair, vertical rule has been glued with "Patafix" (from UHU company)
webframe01.jpg

Under  the roof we have "Patafixed" 3 coded targets to get the roof plane
roof01.jpg

Then some on the inclinated plane which was too small for using the rules
inclinated01.jpg

As I did'nt know the space I will have arround the Webframe, I have used an Ultra Wide Angle Tamron 11mm freshly calibrated plugged on my old Nikon D60 (after that test, I saw  it would work with a regular Nikkor 18mm).

After one or two tests to learn how to take the shoots in this narrow area, it looks the full webframe area can be digitized with 12 photos.

Then I ran Rhino > Rhinophoto
rp01.jpg

One minut later, I got the 3D points.
3dpts01.jpg

I launched the countertop application and enter the thickness values of plates.
plates01.jpg

Finaly... less than 10mn Rhino surface command to finish the plates to cut...
3d_surfaces.jpgsurfaceswithphoto.jpg

unfold01.jpg

Duration to digitize the 4 plates :

- 5mn positioning the rules
- Less than 5mn taking shots + Rhinophoto computing
- 10 mn finishing the drawing in Rhino

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Welcome to my blog

Welcome to my blog,

I will add information, tips & tricks, results of Rhinophoto tests, ideas, development status...

Everything on Rhinophoto which could help customers.

Do not hesitate to contact me if you have any questions : support[at]rhinophoto3d.com

Philippe BOICHUT
Technical Manager

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