About 3D Measurement

Crime Scene Virtual Tour (CSVT)3.00 makes a breakthrough in virtual crime area. With CSVT 3.00, you can look at the scene and get an accurate 3D measurement of important objects from any angle and have an overall idea on the place without losing any suspicious clew.

How to Improve 3D Measurement Accuracy

• Equipment
  （1）The performace of the digital camera, including resolution, effective pixels and imaging quality will affect the accuracy of measuring result. For example, if the camera is with a low resolution and less effective pixels, then the collected image information is also very limited. Since panoramic measurement depends on the pixels of the orginal images, the accuracy of measurement will be decreased a lot. Furthermore, low image quality and inaccurate measuring point choosing will also cause error. We recommend digital camera with more than 8 million effective pixels.
  
  （2）The stability and the max vertical adjusting height of tripod. You should choose a tripod with good stability and gear wheel axis. The more difference between min and max height, the better. We recommend Manfrotto 028 as the shooting tripod

• Photography:
  （1）Choose big size mode and Fine quality during photography. Use manual mode to ensure the two sets of images are applied with the same shooting parameters.
  

  
  （2）To realize 3D measurement of any two points in the panorama, you need to get two panoramas in the same location, with the same photography and stitching parameters at different height. Horizontal movement or error will easily be caused unconsciously during height adjusting. The suggested shooting process is:

  1) Fix tripod and rotater first
  2) Shoot the first set of imags at normal height
  3) Turn the camera back to the first shooting angle
  4) Upgrade the height of tripod
  5) Shoot the second set of images

  Notes:
  （A）The first shot in two sets of image at different height should be set at the same position, there should not be any difference between them except vertical height.
  
  （B）The lens should be kept at the same angle vertically during rotating and height adjustment.
  （C）The tripod should not be moved horizontally while adjusting height.
  （D）The first shot in both two sets of shooting at different height should be kept at the same initial angle. Suppose the angle of the first shot is at zero degree, the corresponding first shot of the second set of images should also be kept at zero degree.
  （E）The change of vertical angle of lens and horizontal movement of tripod should both be avoided during photography.

  （3）Make lens in front of the measuring object when shooting. Avoid the measuring object being located at stitching seam.

• Stitching:
  Apply the same stitching parameters for 2 sets of source images during stitching.
  Method 1: Import the first set of source images into Stitcher, stitch them into panorama and save the relative stitching parameters. Then import the second set of source images and use the stitching parameters from the first set and stitch.(Panorama->Stitch with Former Parameters)
  Method 2: Use right-click stitch for measurement. You can apply the same stitching parameters to stitch multiple set of source images.

• Choose measuring point correctly to avoid errors:
  Insert measuring points by both probable and accurate adjustment 1) Import the panorama which is shot at normal height as Main Panorama and import the second panorama which is shot at higher position into Assistant Panorama. 2) Adjust the percentage to display panorama at 100% 3) Drag both Main panorama and assistant panorama to make the measuring object being displayed in the viewport properly 4) First insert starting point in the left window (Main Panorama) and then insert the relative starting point in the right window (Assistant Panorama).
  Return to the left side, insert the ending point, go to right side and insert the relative ending point. If Auto-switch under the leftside flash is selected, after you insert a measuring point in one side, the cursor will automatically switch to the other side. 5) When inserting measuring point in right window, you should pay attention to the magnifer beside the cursor to make sure the measuring point is at the same
  position with the one in left side. If they’re not consistent, you may adjust them by selecting the point and press the up, down, left, right key on keyboard to make a further adjustment.
  Also pay attention to the manifer beside your cursor during making accurate adjustment.