Measure dimensions with lower than 1% error
Yes, it is true that you can achieve +/- 1% or lower dimensional measurement error for each 20 meter (or 65 feet) range as long as the setup is right. The most critical setup for highly accurate dimension measurement is to figure out the right absolute scale of a section. Because the result of photogrammetry processing is all based on relative coordinates among photos, it’s not possible to measure an absolute distance until the scale factor is calibrated.
Keep in mind:Our software uses a few assumptions to determine the default scale when processing photos. However, please keep in mind that it is just for making the result look visually reasonable, and you have to scale it right using methods explained in this article to be able to measure dimensions.
DISCLAIMER:Although Cupix’s measurement can be very accurate, the intended goal of this feature is for planning purposes. We wouldn’t want anyone measuring dimensions where organizational guidelines or any regulations require high accuracy.
Methods to calculate the absolute scale
Mainly there are three ways to get the absolute scale.
Use markers - automatic and the most accurate method
By placing market sheet papers in the scene, which can be downloaded here "Downloads", while you take photos, you can automate the scaling step with the best accuracy. Our processing software can recognize markers and calibrate the scale automatically. When markers are correctly recognized, the scale status will be set to Scaled by auto-detected markers.
Use a known dimension
The second method, which may be the best choice when market sheets are not available, is to use one known dimension as the reference dimension, or the real value.
- Measure a dimension that you know the real value using button available in the Editor toolbar.
- Right mouse click on the dimension and select Scale menu.
- Enter the real value you already knew.
Use the average camera height - the simplest method even yet ballpark estimate
By using the estimated average camera height, you can scale a section reasonably well even if you are not allowed to use marker sheets, or you don’t know any reference dimensions. To make this technique work, you have to make sure that two pieces of information are well defined before you set the camera height value.
The floor is the vertical origin of a section in the 3D space. Please refer to "Get used to Cupix Web App" for details. The floor can be easily adjusted by clicking the Adjust Floor button and picking a common floor point from two different panos. It is rendered in a blue plane in 3D mode.
Current Pano was Taken on the Floor
This information implies that the pano you are seeing in the Editor has been taken on the floor. Our processing software tries to detect whether a pano has been taken from a floor based on some assumptions, but it could be incorrect, and you can freely change it to make it right. If this information is not correct, the scale factor calculated using the camera height would be incorrect.
Now you are ready to enter the approximate average height from the ground where the camera has been placed on to the lens center in the Adjust Section interface, and you can get a moderately estimated absolute scale factor.
Methods to pick a 3D point when measuring a dimension
There are four options available whenever you need to define a 3D coordinate position such as endpoints of a dimension, the anchor point of a pushpin object, the location of a hotspot object, etc.
Pick a common point from 2 panos
You can define a 3D point by identifying a common point from two different panos. Granted that picking a pixel can include a human error, this method can be pretty accurate. When you pick a pixel from the first pano, dynamic hint line will appear in the other pano indicating that the matching pixel should be on the line. Plus, because your mouse pointer will be auto snapped on the hint line, it is effortless to pick the right matching point. Therefore, using this method, you can pick fairly correct 3D points from any surfaces even when the underlying 3D mesh is not, under or over-represented.
Pick a point on the floor
The second method is to pick a point from the floor. A floor is an infinite plane even if it is rendered by a plane with bounds. This option is useful when you measure dimensions for floor plan generation.
Pick a point on 3D boxes
Finally, you can pick points on 3D boxes. This method is useful when you know where to locate reference 3D boxes.
Pick a point on 3D mesh
Using this method, you can pick a point on the underlying 3D mesh. In case the geometry of interested wall is well generated, and you want to measure wall-to-wall distances (rather than point-to-point), you should use this method. The easiest way to check the quality of the 3D mesh geometry is to make sure wall-lines of the auto-generated blue sketch in the Layout tab look clear and correct.
Factors affecting the measurement accuracy
There are several more factors other than the absolute scale which can affect the accuracy.
360 camera vendors use different parameters when stitching photos from multiple fisheye (or wide-angle) lenses, and they may make an effect on our photo positioning accuracy. The best cameras in this regard are Ricoh Theta V, Insta360, MadVenture 360, Yi 360 at the time of writing.
Enough overlap among 360 photos
Our server processing primarily relies on the common image areas among photos, and therefore enough overlap is also vital to achieve the reliable result. Please refer to "How to take 360º photos and 360 videos" for the details.
Eyeballing when picking a point
You should expect a human error like when you use a tape measure or other measuring devices. Again Common Point from 2 Panos would be the best option to minimize this point-picking inaccuracy.
Measure dimensions in the Web Player
You can allow your Web Player viewers or workspace users with the Review-Only permission to measure dimensions by switching on Enable Measure option in the Customize Player menu.