Scale bars

[KurtH]

One thing I've been thinking about as I'm doing more Kintsugi tests is the CHI scale bars are kind of bright and reflective which may not be ideal for on camera flash. Obviously they can be removed from the scene when at lower angles but wondering if dark/black scale bars would be advantageous. 

For Carla/Mark: I don't know how much revenue the scale bars make for you, but a could be an opportunity for a "pro" scale bar in black and if it's a higher end product there are some places that make coded targets that are printed in a process that is finer resolution if doing very high resolution photogrammetry if they were tipped into scale bars, just a way to justify a higher price for useful but smaller market item.

[Michael Tetzlaff]

I know @Charles Walbridge in some cases had to move the scale bars further away from the object than normal in order to minimize reflections.  He could probably speak to that.

In general, you're right that the reflections of the scale bars would influence the reconstruction in Kintsugi.  For the time being, moving them further away away or doing a second pass without scale bars (on a turntable) would be the workaround.

Would be interested to hear @cdschroer's thoughts about the idea of dark scale bars.

[cdschroer]

Our scale bars are based on a design from Tom Noble and Neffra Mathews at the US Bureau of Land Management.  They had made various scale bar designs before this one, and this one includes a gray scaled background photo. That image is spread across a whole sheet of bars - so you can't make out the full image in a single bar. The image is there to give the software more interest points (key points) to match on, so that the scale bars can be modeled, and may also aide in project alignment.  

We usually have the scale bars in a separate set of photos next to or in front of the object and then those images are "disabled" once the project is fully optimized and the scale bars have done their job.  This also ensures that the images with the scale bars have good look angles with the camera perpendicular (or close to it) to the bars - which reduces marker error.  Oblique look angles on the scale bars will increase the marker error - and while you can remove those projections, it's extra work to do so.

So, in our general work flow (and yes, there are exceptions) the scale bars wouldn't be included in the photos used for building the final model or texture map, and therefore I don't think they would be seen by Kintsugi.

Our scale bar product is pretty low-volume - we sell 40-60 sets a year.  And our vendor does not have the ability to print higher resolution targets.  We ran tests with their equipment and the materials we need to make them weather resistant - and the bars we sell are our best option - especially to keep them at the current price point.

Carla

[Dave Martin]

Re:

On 7/8/2024 at 4:05 PM, KurtH said:

... I scale bars are kind of bright and reflective which may not be ideal for on camera flash.....

and

On 7/10/2024 at 8:56 PM, Michael Tetzlaff said:

.... move the scale bars further away from the object than normal in order to minimize reflections....

and

On 7/13/2024 at 1:34 AM, cdschroer said:

... We usually have the scale bars in a separate set of photos next to or in front of the object and then those images are "disabled" once the project is fully optimized and the scale bars have done their job.  This also ensures that the images with the scale bars have good look angles with the camera perpendicular (or close to it) to the bars - which reduces marker error.  Oblique look angles on the scale bars will increase the marker error - and while you can remove those projections, it's extra work to do so.

So, in our general work flow (and yes, there are exceptions) the scale bars wouldn't be included in the photos used for building the final model or texture map, and therefore I don't think they would be seen by Kintsugi. ...

 

I haven't evaluated this effect using Kintsugi, but whilst fully agree with Carla that disabling scale-containing images would mean as you say that they wouldn't be 'seen' by Kintsugi, they will however still have an effect with potentially introducing reflected illumination in other non-disabled images. 

I wonder if, in addition to disabling images as Carla suggested, once sufficient frames have been captured with the scales, maybe the scales could be carefully covered with a suitably optically-dead / black material to prevent (or significantly attenuate) any spurious extra light reflected from the scales in the images to be used by Kintsugi?

Dave

 

 

 

[Michael Tetzlaff]

@Dave Martin If I understand what Carla was saying correctly, it wounds like their recommended workflow is that after taking some shots with the scale bars, you just physically remove the scales before resuming the rest of the capture session.  I imagine covering them with black material would accomplish the same thing, but in most cases, wouldn't it be easier to just take the scale bars out altogether?

[cdschroer]

Hi Folks - we generally shoot the scale bars sufficiently next to or resting on the subject - depending on the subject - and then remove them from the scene.  So the scale bars are in a total of 12 - 25 images, which we manage and name so that we can easily find them and turn those images on and off as needed during the processing.

Here's a link to a time lapse of shooting an outdoor kiosk as part of a training class.  You can view the video on the dropbox without downloading it.  In this case, there are some scale bars set leaning against the building (it isn't delicate artwork). And another set laid out on the ground next to the building.  This was for practice during training - and you do NOT need multiple sets of scale bar to set scale on a subject (though you should have 3 or more scale bars in your scene).  After they were shot, they were removed, and the whole kiosk was shot.  I think this illustrates a couple of options for setting up scale bars. 

The scale bars are not casting reflections on the subject in any images that will be used to build final texture maps. The scale bar images are helped in the alignment because of the background image printed on the bars. (i.e. you get a lot of key points and tie points on the bars themselves - which can help your overall project)

One note about the scale bars on the ground is that a set of images was taken going over the top of the scale bars in strips, then tied into images that include part of the kiosk by tilting the camera 15-20 degrees at a time (and changing the location of the camera - you never want to just rotate the camera in place like a pano). The distance to the subject for the primary shooting was already determined, and that distance was maintained for shooting the scale bars so no focus changes are needed.  

For turntable projects we have stands or magic arms, that let us put the scale bars next to the subject, and take those photos by moving the camera and not turning the turntable.  Here's an example of a setup: 

 

The scale bar holder with the bars is removed as soon as the scale bar shots are taken and before the turntable is used to create circuits.

[Charles Walbridge]

@KurtH The scale bars are definitely reflected in an object like the censer in the attached photos. One workaround I've developed for turntable photography is to do a full or partial photogrammetry set with the scale bars in place, then another turntable set with the camera moved a bit - in this case the camera is raised about five centimeters, and the object is turned five degrees, before starting the set. Then I use the scale-bars set and the not-scale-bars set to build in Metashape. This has the advantage of giving me twice as many angles of the object, and Metashape has no trouble separating the two different heights. For the final model texture in Metashape - and for the texture build in Kintsugi 3D Builder - I'll turn off the set of photos with the scale bars in them.