checkerboard traget not founded...

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myvisuals
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checkerboard traget not founded...

Post by myvisuals »

hello,

doing some testscans in a house, placed on the walls checkerboard targets... but the are not recognized by the software, have to select them manual... don't think this is normal ? It's the offical faro checkerboard.
have 6 scans, overall the same problem...
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Re: checkerboard traget not founded...

Post by Scott »

It could be the lack of contrast of your black and white targets. The black should be very black -not grey, as shown.
Print them with a xerox machine, too.
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checkerboard traget not founded...

Post by 3DForensics »

If you can find them manually you might not have selected them in the preprocessing?? The contrast and size look sufficient.


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myvisuals
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Re: checkerboard traget not founded...

Post by myvisuals »

well, in the colored version, so after the preprocess scan option they were recognized after a new search target option, but will go to the print service and see if it is possible to make this more black.
To remove the reflection problem, i suggest to use a clipping box, correct ?
Other problem ( still waiting for my training day at faro campus holland ), have done 6 scans, 4 are good recognized, other 2 not ( lack of good target placement ).
is it possible to fix this manually in stead of returning to the site ?

I love this forum... ;)
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Re: checkerboard traget not founded...

Post by geowac »

Vincent,

my be your checkerboards are reflecting too much!? Your references should be 100% black / 100% white. I get very good results with ink jet printers. Some copiers make too shiny black (its very reflective sometimes). If the laser is reflecting too much, the result will be gray...

I guess, with the colored images the black is really black ? SCENE does use the colors of the scans, while target recognizing is running - therefore if the scan is colorized, it will use the color information, too.

I get no targets recognized, which are too far from the horizon. I did not yet calculate the angle, where targets are recognized, but the actual version seems not to find all targets in a scan...

The scans you get not register: Move them in Correspondence View, try the "top view based registration" or use a natural target and use the 3D-Point-Selector (which uses the center point of a 3x3 pixel array) in the overlapping area.
geowac_natural_targets.jpg
I guess, you have enough overlapping 8-)

Good luck
Stefan
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Re: checkerboard traget not founded...

Post by dan_mccurdy »

myvisuals wrote:well, in the colored version, so after the preprocess scan option they were recognized after a new search target option, but will go to the print service and see if it is possible to make this more black
The Scene manual recommends only doing target recognition on black/white scans, otherwise you are registering to a photo draped on a scan, which is (at least theoretically) less accurate than the scan itself. So if you have already coloured them you should remove the colour (revert to greyscale) and then manually pick the targets.

Also - I recall that the "black" on scanner targets is actually supposed to be a medium grey rather than black (I think I read that in old cyclone documents, but I imagine the same still applies to Faro as well). The official Faro targets are grey rather than black, as are Leica's. From memory this is due to grey providing much better scanner return than black, while still contrasting with white.

We have printed the official targets onto shiny vinyl magnetic sheets and they work fine for most work, but ironically they freak out when the scanner is looking at them straight on (stupid reflections). We couldn't source any matte vinyl magnetics at the time.
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Re: checkerboard traget not founded...

Post by myvisuals »

Thanks Stefan for the info, will try that.

So dan, you think that the black ones will not work properly ?
I have designed the in my CAD software, realy black, not darkgrey.
I will do a testscan on thursday and use both of them ( 1 room official faro targets, 1 room designed targets black )
But manually placing targets give weird results, rooms are not good connected, or i do it not good ;)

keep you in touch

regards
Vincent
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Re: checkerboard traget not founded...

Post by myvisuals »

to understand it well
in a big room where i have to use for example 8 scans i don't have to use additional targets because the scans recognize each other.
in different smaller rooms i have to use targets for overlapping…

Correct ?
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Re: checkerboard traget not founded...

Post by geowac »

;) It's nearly right!

Place a scan in front of each door and one inside small rooms, if all scans are on one floor, "top view based" registration should do it! Improved by "cloud to cloud" ! Targets are uses to easily check the registration quality or on huge projects to decrease the needed time to get the scans registered! Small projects will succeed without targets, too!

I recommend to have an overlapping of at least 30% between scans you have to register! More is better!

Because scanner are fast today, a few more
Scans will not heavily increase on site time!

I get often projects, other gave up while registration, but there were no project I did not get registered even if some scanning rules were violated ;) only one time I had scans without any overlap - this was indeed heavy, but nevertheless possible (some assumptions needed)...

Some rules:
- have an overlap of at least 30%
- make additional scans in front of doors if the rooms behind are necessary
- with targets have at least 3 targets overlapping and close loops!
- with targets a main scan with hight resolution covering most overlap area with the following scans will help a lot (seeing most references)
- make some additional scans, if uncertain overlapping area is acceptable

Cheers
Stefan



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Re: checkerboard traget not founded...

Post by myvisuals »

Thanks stefan for the good explanation... good forum here ! ;)
So for this kind of scanjob i do not really need targets...
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