Adding Precision Markers

[sarko]

Hello,


I have been using Photoscan for a couple weeks now and have been very happy with the results thus far.  One problem I have is with the positioning of markers.  I am ingesting aerial imagery and trying to apply ground control to them.  My workflow is as follows:

1.  Ingest images  -- No problems here
2.  Compute geometry -- no problem here
3.  Build Texture -- no problem here

When I build my texture I generally choose a single image to use as the orthoimage.  The texture looks nice and at this point I try to apply my ground control.  I have precision GPS measurements for points in my image, but what I find is that with the way Photoscan allows you to navigate the image (i.e. the trackball function) that I cannot zoom into specific areas closely enough to put down my marker in what I feel is an accurate manner.  

Am I doing something wrong?  Is it possible to apply the markers earlier in the workflow, but I don't really see how?  Any help you can provide would be great.  


Thanks,
Scott

[GPC]

I agree, I think this is one area that the software could be drastically improved.

Ideally the user could set the desired coordinate system, import a CSV of coordinates and drag and drop the "markers" for each point into the model and place it accurately. Currently it is a first rate pain to place a dozen markers and make sure that the point in the photo is the same as what I've added to the XML.

One tip for placing the point more accurately and being able to zoom in better, turn the model on its side and use the CTRL, SHIFT and ALT buttons to zoom and pan into near where your target it. By approaching it from the side, you can place the camera directly over the target and then rotate the screen to look more closely at the target. In this way you can get an extreme close up of the target.

[sarko]

cs,


Thank you very much for the suggestion.  I will try that.  I know that Dmitry is working on improving the capabilities with aerial photography and hopefully this will be one are that can get better.

[Dmitry Semyonov]

Hello Scott,

As cs suggested, to zoom into specific areas closely, it may be required to pan the model so that the area of interest is close to the center of rotation. Then it will not disappear during zooming.

There is also a different approach to marker placement. You can first create the marker instances using "Add Marker" command from the chunk context menu. After the marker instance is created, you may specify projections of the marker on the source photos. To do that, open the photo where the marker should be placed and switch to the marker editing mode using "Edit Markers" command from the Photo menu. While in the marker editing mode click with the right mouse button on the location where the marker projection should be placed, and select the marker instance from the "Place marker" submenu.

Using this approach it is possible to define markers without reconstructed geometry or model texture. The disadvantage compared to the model-based marker placement is that marker projections on each photo should be individually defined.

With best regards,
Dmitry Semyonov
AgiSoft LLC

[Nathan Craig]

If markers are placed on the models and then marker positions are refined in each of the photos, does this update marker position on the model? Often times, it is difficult to get highly accurate placement of the targets on the models. This is because textures are more coarse than the source photos and because I use colored photo targets that are flat and don't produce sharply defined features in the models. In other words, markers are placed on the model largely based on the textures but the textures are not as finely resolved as the source photos. The textures do provide sufficient resolution to place markers, but marker position can be refined by returning to the source photos. However, I am not clear if calibrating marker position on the source photos has any impact on maker placement on the model. Is this the case?

Thanks,
Nathan

[Matt]

Hi Nathan,

Short answer is yes refining the marker position on the photos refines the position on the surface, just make sure you change them on all the photos.  I have had good results even with old scanned analogue photos in producing registered DEMS using high resolution orthos and LiDAR for XYZ control.

Matt

[Nathan Craig]

Thanks Matt, that is useful information regarding the markers. Also, the ability to create DEMs from archival aerial photograph is quite interesting. I've tinkered with this only a bit in terms of trying to reconstruct archaeological mounds that are now destroyed but visible in old aerial photographs.