Trim a drone point cloud to the area of interest

Why trim before you export

EOMeasy triangulates the points into a surface and, if you do not give it a boundary, measures over the area both surveys cover. That is deliberate and it works well, but it means anything both flights happen to cover counts toward the volume: a car park, a haul road, an untouched stockpile, vegetation, or the extra ground a drone always captures past the edge of the pit.

Trimming the cloud to your area of interest in the processing software is the cleanest way to scope the measurement. It also keeps the file small and fast. The alternative, giving EOMeasy a boundary string, works just as well when you have one; trimming at the source is simply the simplest path when you are working straight from a drone.

Best practice, whatever software you use

• Trim to the area that moved, plus a small margin. Leave a few metres of stable ground around the edge so the surface triangulates cleanly right up to the boundary of the work.
• Trim the same outline on both surveys. Use the same area of interest for the start and the end flight so they cover the same footprint. If one is trimmed tighter than the other, the overlap, not your intent, decides what gets measured.
• Keep the coordinate grid and height datum identical. EOMeasy does not reproject. Both clouds must sit on the same grid and the same height datum as the rest of your survey, or the volume is wrong. See Coordinate grid and height.
• Export LAS, LAZ or PLY. EOMeasy reads all three. Only the X, Y, Z of each point is used; colour, intensity and classification are ignored, so you do not need to strip them.
• Bare earth under grass? Trimming does not remove vegetation. On photogrammetry over grass or scrub, set Ground points to Lowest in EOMeasy so the lowest shot at each spot wins. See Point clouds.

DJI Terra

Terra trims by reconstructing only inside a Region of Interest (ROI). You set the ROI before you build the cloud; there is no separate crop-after step, so define it up front.

1. Create the mission and run aerotriangulation. Terra needs aerotriangulation done before the ROI page is available.
2. Under Advanced Settings, click ROI to open the Edit ROI page.
3. Define the area of interest one of four ways: KML Import to bring in a polygon from GIS; type minimum and maximum coordinates and click Apply; use Reset Region then Auto or Max Region for a quick box; or click the edit icon and click on the map to drop the corners of the area, then set a height range.
4. Set the Output Coordinate System to match your survey (choose Known Coordinate System, your horizontal datum by EPSG code, and your vertical datum and geoid, for example AHD).
5. Under Output format, select Point Cloud and tick LAS. PNTS stays on by default for Terra's own display; LAS is the file EOMeasy reads. Terra writes LAS 1.2 and does not export LAZ, which is fine, LAS is all you need.
6. Click Start Processing. Because reconstruction is confined to the ROI, the LAS Terra writes (in the result folder, under lidars\terra_las) already contains only your area of interest.

DJI documents the Region of Interest, with screenshots, in DJI's guide to the Terra Region of Interest.

Pix4D

Pix4Dmapper trims with a Processing Area polygon. If a Processing Area exists, only points inside it are written to the densified point cloud and to every export.

Draw the area in Map View

1. On the menu bar, click View → Map View.
2. Click Map View → Processing Area → Draw, then click OK on the how-to popup.
3. Left-click each corner of the area, then right-click to place the last corner and close the polygon.
4. Click Project → Save Project.

To bring an outline in from GIS instead, use Map View → Processing Area → Import… and choose a .shp or .kml file. It must be a polygon, not a line; any coordinate system is fine, Pix4D transforms it into the project's. To nudge corners later, use Map View → Processing Area → Edit….

Generate the cloud inside it, then export

1. Open View → Processing, tick 2. Point Cloud and Mesh, and click Start. Re-run this step if you changed the area after a first run, or the file on disk will still hold the old points.
2. Open View → rayCloud. In the left sidebar, expand Layers → Point Clouds → Densified Point Cloud.
3. Right-click the densified point cloud and choose Export Point Cloud….
4. Pick LiDAR LAS File Format (*.las) or Compressed LiDAR LAS File Format (*.laz), set a name, and click OK.

Pix4D documents these steps, with screenshots, in its Processing Area article and Export Point Cloud article.

Agisoft Metashape

Metashape Professional gives you two accurate ways to trim the cloud you already have, and you can use either.

Select the area, then crop

1. In the Model view, pick a selection tool from the toolbar, Rectangle Selection or Free-Form Selection, and draw around the points over your area of interest.
2. Click Crop Selection on the toolbar, or choose Edit → Crop Selection, to keep only the selected points and discard the rest.

Clip to a polygon at export, for an irregular area

1. Draw a polygon in the view, or import one from GIS, to use as a boundary shape around the area of interest.
2. Choose File → Export → Export Point Cloud. In the Export Points dialog, set the type to LAS (*.las) or LAZ (*.laz), and tick Clip to boundary shapes so only points inside your polygon are written.

The Region bounding box (the Resize Region toolbar tool) is a different control: it limits what a rebuild of the dense cloud covers, not a crop of the cloud you already have. So to trim an existing cloud, use selection and Crop Selection, or the export clip above. There is no Workflow > Crop menu in Metashape; cropping lives on the Edit menu and toolbar, and clipping at export lives in the Export Points dialog. The current steps and dialogs are in Agisoft's Metashape user manual.

Then, in EOMeasy

Drop the trimmed LAS into the Start surface or End surface field, the same place a Vulcan or PointStudio surface goes. Leave the Boundary blank to measure over the trimmed footprint, or add a boundary if you want to scope it further. Run the period, and the plan-view render, PDF report, CSV and running totals all come out exactly as they do from a CAD surface. See Point clouds for the gridding controls and Reading your results for the report.