Metashape Processing Script: "Cameras" may contain elements that are not cameras, and therefore no "labels" tag

[Jordan-Pierce]

Hi,

This probably isn't worth a PR, but we use Metashape (and now NeRFs 😎) for underwater reconstructions. Because we already use Metashape, the processing script is very useful, which allows us to skip the redundant step of using colmap.

We use Metashape 2.0.X, and when exporting cameras as an XML file, "cameras" may contain elements (children) that are not really cameras, and therefore they will not have a "label" tag. This results in the processing script to throw an error which checking:

assert isinstance(camera_label, str)

Simple fix is just to check if the value returned in the previous line (camera_label) is None, since if labels does not exists it will return None; if None that iteration is the looped is skipped. This worked for us.

Below is the end portion of the xml file exported from Metashape 2.0.X:

      <camera id="64" sensor_id="0" component_id="0" label="T_S04920">
        <transform>0.39032194793077357 0.74216472892988283 -0.54483051685451722 3.7012935179350013 0.14664850872693375 -0.63433252101113768 -0.75902336438071649 4.910698514524003 -0.90892408475718844 0.21636489530441105 -0.35643125596420205 -3.9777394049343489 0 0 0 1</transform>
        <rotation_covariance>1.394591407696673e-06 -3.7607955822753534e-07 1.1867952488316718e-07 -3.7607955822753529e-07 7.7758664650666157e-07 1.0920034902583434e-07 1.1867952488316716e-07 1.0920034902583431e-07 2.4620179263634537e-07</rotation_covariance>
        <location_covariance>6.393339613270235e-05 1.5684529424959145e-05 -9.0286930149678477e-06 1.5684529424959145e-05 3.2236122010502187e-05 3.444842030555343e-06 -9.0286930149678477e-06 3.444842030555343e-06 3.6920228505667884e-05</location_covariance>
      </camera>
      <camera id="65" sensor_id="0" component_id="0" label="T_S04921">
        <transform>0.56545362962624202 0.70118479953823465 -0.43428339783951486 2.6437300931218672 0.092622773201603864 -0.57719846981802292 -0.81133405470507514 5.0063193906986267 -0.81956281920726037 0.41854725340904952 -0.39132465043335568 -3.6004257300682041 0 0 0 1</transform>
        <rotation_covariance>1.209912231499636e-06 -4.4062191099276087e-07 2.0903343133076167e-07 -4.4062191099276087e-07 8.6328746534497716e-07 6.2709444009263899e-08 2.0903343133076165e-07 6.2709444009263846e-08 2.8208165478935081e-07</rotation_covariance>
        <location_covariance>4.2212494553780979e-05 2.3469769781825893e-05 5.1680234333248182e-07 2.3469769781825893e-05 2.2473232564370221e-05 4.4297157515358392e-06 5.1680234333248182e-07 4.4297157515358392e-06 3.3530347492313847e-05</location_covariance>
      </camera>
      <camera id="66" sensor_id="0" component_id="0" label="T_S04922">
        <transform>0.64117720350252272 0.72149375025577123 -0.26141645328966501 1.5613630239847063 0.12154389829048877 -0.43183443847192948 -0.8937259638938464 5.3822534643500592 -0.7577063247043907 0.54126313941695392 -0.36457556063382468 -3.9451381019346581 0 0 0 1</transform>
        <rotation_covariance>1.2430414050643863e-06 -4.5452791721409356e-07 2.1446299263309236e-07 -4.5452791721409371e-07 9.545917766663648e-07 7.8385516624294453e-08 2.1446299263309241e-07 7.8385516624294426e-08 3.9795996173449087e-07</rotation_covariance>
        <location_covariance>3.0764706874131967e-05 2.7518646887297614e-05 8.8649240493325569e-07 2.7518646887297614e-05 3.5041290611447137e-05 9.0326111993099262e-06 8.8649240493325569e-07 9.0326111993099262e-06 3.6558310833773086e-05</location_covariance>
      </camera>
      <camera id="67" sensor_id="0" component_id="0" label="T_S04923"> # <---- Last actual camera in chunk
        <transform>0.6315650967128067 0.74141350874269529 -0.22678522365442563 1.2397219316611183 0.13016714853995587 -0.38974707713962597 -0.91167632924305742 5.4529344464741705 -0.76431802415952466 0.54626296315507528 -0.34265833278926217 -4.3576834429046816 0 0 0 1</transform>
        <rotation_covariance>1.3276245073228852e-06 -4.4641590558287118e-07 2.2027657676088766e-07 -4.4641590558287113e-07 9.6577120715844808e-07 1.0265997372360024e-07 2.2027657676088766e-07 1.0265997372360016e-07 4.294940980769791e-07</rotation_covariance>
        <location_covariance>2.4441292417832514e-05 2.9474714336166356e-05 2.9557108459981755e-07 2.9474714336166356e-05 3.8066356850846667e-05 1.0009325305418448e-05 2.9557108459981697e-07 1.0009325305418447e-05 3.6954974814697176e-05</location_covariance>
      </camera>
      <camera id="68" type="keyframe"> # <--- Other information stored in XML file
        <meta>
          <property name="PlanMission/AircraftAction" value="0"/>
        </meta>
        <transform>-0.99682412419370503 -0.017262323194525045 -0.077741093530906746 -0.3049857777952798 0.057388794930530479 -0.83253161300054657 -0.5509969506005723 10.659801178865708 -0.055210430553247314 -0.55370852039013796 0.83087825991867736 -21.587381935976197 0 0 0 1</transform>
      </camera>
      <camera id="69" type="keyframe">
        <meta>
          <property name="PlanMission/AircraftAction" value="0"/>
        </meta>
        <transform>-0.99905544537165425 -0.033548551524815381 -0.027617236716094801 -1.2537197036765357 0.043230317883591933 -0.83171056854943337 -0.55352386559105271 10.707630099695644 -0.0043996237259110805 -0.55419493398421193 0.83237528702941765 -21.615717353443586 0 0 0 1</transform>
      </camera>
      <camera id="70" type="keyframe">
        <meta>
          <property name="PlanMission/AircraftAction" value="0"/>
        </meta>
        <transform>-0.99850221983583265 -0.049848472990305176 0.022548763235492587 -2.2032513060763739 0.028951350187054671 -0.83112157152507093 -0.55533661203637752 10.741941386994524 0.046423445641852329 -0.55385202273371803 0.83131991471906097 -21.59574148608425 0 0 0 1</transform>
      </camera>
      <camera id="71" type="keyframe">
        <meta>
          <property name="PlanMission/AircraftAction" value="0"/>
        </meta>
        <transform>-0.99516598952503266 -0.066116656786366107 0.072617084684370434 -3.1509340701138302 0.014591689884920656 -0.83076626356780714 -0.55643013748707704 10.762639409050678 0.097117124540245015 -0.55268074239381559 0.82771508449952469 -21.527510010223331 0 0 0 1</transform>
      </camera>