Using UAV generated data for an elevation survey
28 Feb 2019
UAV's and surveying - practical applications

This year we have been looking at practical ways of using UAV’s in surveying to complement our existing services and bring greater clarity to our deliverable products.

Using UAV’s in surveying allows us to gather far more data in the same time as traditional techniques but it’s how that data is utilised that is important.  If it cannot be transferred into a usable drawing or model then the data is worthless.

Recently we had a job to carry out an elevation survey on a timber frame property that would lend itself well to conduct a comparison between traditional techniques and using the UAV and to see what the time saving and data quality comparisons would be.

The property was to be surveyed on a local grid using a Topcon DS-103 total station fully but there were to be some ground control points (GCP’s), marked on the house to be identified in the photogrammetry to transform the generated point cloud onto the same grid to make a comparison.

The total UAV preparation and flight time was approximately 30 minutes and the site survey time was approximately 3hrs, this included fixing the GCP’s.

The photogrammetry reduction was done using pix4d software (by www.pix4d.com) which generates a .las and allows you transform it onto your required grid. The image below shows the pix4d generated .las point cloud.

UAV Generated Point Cloud

The surveyed data was reduced and processed in n4ce (by www.appsincadd.com) and it also allows you to import and compare the two data sets using their point cloud function and allows you to extract a geotiff of each elevation aligned to the correct grid to be used as a back cloth.  The comparison between the data sets was very good and generally the difference between them was no more than 15mm which on a non linear building such as this was within tolerance.

Elevation With Geotiff

Final Elevation Checked with UAV Generated Data.jpg

That said though, it would not be advisable to use the UAV data as a standalone data acquisition tool.  You still require the total station to set out the GCP’s and it would be highly advisable to carry out some check measurements with the total station for QC purposes in addition to the GCP’s.  Also the UAV can only position things it can see, so the operator must recognise the need to pre-empt the short comings of the UAV and measure up in areas where data may be missed.

Currently the UAV isn’t a one stop shop for this type of work but it does compliment traditional techniques and with a well laid out work flow can considerably reduce the time spent on site and gather enough information to be used as an office based field checking tool and negate the need to return to site for those sometimes missed critical pieces of data. Anything that brings greater clarity and information to a survey is a bonus it’s just having the knowledge of how best to apply it that counts.