Drone photogrammetry for stockpile measurement

Republished from Nov 2016

Of the biggest 40 mining companies announced in PWC’s mining report, nearly half of them use drone photogrammetry software (Pix4Dmapper) as part of their mining workflow.

 

Managing stockpile inventory, that is, finding a solution for accurate volume measurement and easy inventory management, is one of the biggest challenges in the mining industry.

 

These top mining companies claim that by applying the photogrammetry workflow with Pix4Dmapper, they can achieve measurement accuracies of around 2-5% for their stockpile volumes.

 

Why use drone photogrammetry for stockpile volume measurements?

High-resolution images give you more details of the mapped stockpiles

When it comes to stockpile volume measurements, stockpiles do not conform to a perfect shape. A photogrammetric survey with a fine ground sampling distance (GSD, which indicates the actual distance each pixel represents) is able to better describe irregular stockpiles in detail.
 
Horizontally, high-resolution photogrammetric results create more precise stockpile models, and thus better volume measurement accuracy than ones interpolated from certain measured points.
 
Vertically, they lower the uncertainty in Z values, which is proportional to the resolution. For example, flatter stockpiles will benefit more from a high GSD than taller stockpiles.

 

volume-uncertainty-pix4dmapper-pix4d
Volume measurement of the same stockpile in the data sets of (Left) GSD=2 cm (Right) GSD=20 cm.
Larger uncertainty in vertical direction in low GSD data sets

 

Pix4Dmapper allows you to adjust the reference base above which you want the volume to be measured  

Why is setting a precise reference base important for getting accurate volume measurement?
Imagine we have a 10-meter-tall crushed gravel stockpile in a cone shape, with a 45° angle of repose:

 

volume-pix4dmapper-pix4d-surface

 

The bottom 2 meter section occupies 48.8% of the entire stockpile volume, while the top 2 meter section occupies only 0.008%.

 

The error of the height values will have much more influence for the bottom flat part than the tip. This also explains how important to well-define the base surface is in order to obtain an accurate volume measurement.

Typically, there are several types of stockpiles

stockpile-volume-pix4dmapper-pix4d

 

Standard stockpile is the most generic stockpile type. It is constructed with basic bucket loading and dumping techniques.

 

stockpile-volume-pix4dmapper-pix4d

 

Ramp stockpile is constructed high, with a narrow ramp, and is optimal for storing a large amount of materials in a very limited area.

 

https://support.pix4d.com/hc/en-us/articles/217114246

 

Bin stockpile is a common stockpile type. Materials are stored in a row of three-sided bins, with enclosures consisting of a hard floor and walls. It is the best solution to keep different materials separate.

 

Precise volume measurement in Pix4Dmapper

 

In addition to generating precise 3D models for the purpose of measurements, Pix4Dmapper performs accurate stockpile volume measurements because of its ability to customize base surfaces.

 

The software provides 6 different base surface-defining options in its volume management module; for more complicated conditions, users can import their own base surface (or ground-surveyed points which form the base surface) and use them as a base to calculate stockpile volumes. For more information on this subject, see our support article: How to select base surface for accurate volume measurement in Pix4Dmapper.

 

Read more in our white paper
Data set source: courtesy of Geomatic Development
Author: Lisa Chen

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