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Measurement workflow and examples

Measurement workflow

In Pixpro various measurements are acquired via object layers and with the profile tool from the toolbar. Point, Line and Polygon layers each have their own measuring capabilities as does the profile tool. Profile tool can be launched from the toolbar and from the line properties panel. Only difference is that the tool from the toolbar is temporary and the line object profile is accessible as longs as that particular line is present in the project.

Profile measurement tool workflow

For the profile tool to work a DEM must be present in the project. Digital Elevation Map is generated from the Dense Point cloud which in turns is created from the Sparse point cloud, a.k.a. reconstruction. Orthophoto layer is only optional. With the DEM enabled and ready for work click on "drawing" in the toolbar. If a line has been drawn and is selected when the button is pressed the profile will appear immediately, if a line is not selected, new line drawing will begin. Line can be drawn in whatever shape and with unlimited amount of segments. After drawing is finished press right mouse button to finish. Same button can be found in line object properties, and it will work identically to the profile tool which means that any line object that is drawn in the project can be use as a profile. The profile section will appear on the bottom part of the software window:

"drawing"

This diagram serves as a visual cross-section of the profile and it is interactive. To measure distances and angles on the profile left mouse click anywhere on the diagram to select a point. Select a second point and now the defined section of the profile is measured. The section is highlighted in blue and the measurements appear in the tools panel.

"drawing"

Tools panel explanation:

Properties

Name: - Name of the object. By default the name is "Profile line".

Points: - number of how many points there are in the drawn profile line.


Calculations 2D

Horizontal length: - horizontal length of the profile line. This length is measured as if viewed from above, the surface itself and height differences have no impact to the measurement.


Calculations 3D

Surface length: - measurement represents entire line length measured on the surface. The line is draped onto the surface and then measured. This measurement will always be larger than horizontal length.


Selection


Slope angle - angle between selection points in relation to the ground. The measured cross section shape does not have any influence on this value, it is the angle between the line connecting the two defined points and the ground.

Elevation - this value represents the vertical distance between the user designated points. Horizontal distance and point placement is not taken into consideration.

Distance 2D - the shortest distance between the designated points. The surface of the DEM is not taken into account.

Distance 3D - distance between designated points on the DEM surface. This distance follows the DEM surface and must always be longer than the 2D distance.

Uniform scale checkmark - if checked, the profile will have its axes scaled uniformly, representing the surface as is.

Below a visual illustration of the profile measurements.

"drawing"

Further below there are three buttons:

Create line - temporary profile measurement can be saved as a line for later use. After pressing this button a new line object will be created.

Export - this option allows exporting the line object which would have been created using the tool described above. This line can be imported into another project and profile then could be viewed by selecting the imported line and pressing the show profile button in tools panel.

Hide profile - hides the profile. If a line was not created using the Create line button, the profile will disappear.

Measurements by object

Point

Point object layer is a point in the 3D space of the project. To view measurements always refer to the properties panel when the object is selected in the layers panel. The properties panel will show all the available measurements.

Properties panel goes as follows:

Properties


Name - name of the object.

Ground truth checkmark - if checked, the point will stay in its current position even if the georeferencing of the whole project is changed. In other words points' geographical coordinates will not change even if the whole project is georeferenced to a different geographical position. If this checkmark is not checked the point will always be tied to the 3D reconstruction and if the reconstruction is moved to a new geographical position by changing the georeferencing, the point will move along with the whole reconstruction and their geographical coordinates will change.

Color - set the color of the point.

Radius - set the graphical size of the point by choosing a value from the dropdown menu or entering a number by hand.

Location


Longitude and latitude coordinates of the point. In Pixpro WGS UTM system is used by default, so the coordinates will correspond to this system.

Altitude - point absolute altitude (elevation). Remember that absolute altitude is accurate only if the project has accurate georeferencing such as survey grade GCP's.


The point layer does not provide as much measurements and information but its main use is to mark points in 3D space with accurate projections made from pictures. Then using the snap function we can connect the points with lines or polygons which will give us more measurements.

To place a point - a point cloud, a mesh or a digital elevation map is needed. Points can be added by two methods:

  1. Using Add point button in the vertical toolbar "drawing"

Once the tool is enabled place a point by left clicking anywhere on the DEM or dense point cloud. If you are placing the point on the dense cloud its is recommended to enable snapping in the toolbar. To enable snapping click on "drawing" and when the button turns blue it means that snapping is enabled. With snapping you can use any point on the point cloud to snap to. When placing points on the DEM it is not necessary to use snapping. When a point is placed it can be moved by pressing the right mouse button on the point in the layers panel and choosing Edit Point. Then the point can be dragged to a new position.

  1. Adding a point from projections by pressing right mouse button on points layer and choosing **Add point from projections*

Note: if the points are place using method 1 its projections can still be viewed and edited. The process is identical to the process of placing the point directly from projections and will be described bellow. To edit projections of a point simply double-click on the point in the layers panel or press right mouse button and choose Point editor.

"drawing"

Already familiar window should open. Edit manual point window is identical to that of the GCP projections. All the relevant information is displayed such as point location, point name, amount of projections on photos, etc. On the right we see an estimated projection of our placed point. In this case yellow to grey corner is the target. By placing the point directly on the dense point cloud the target was missed by a few centimeters. But now we can correct that error by adjusting the projection in this window. Left mouse click on corner of the outside window niche on the photo. Repeat this process 3 times and projections should adjust automatically from there. This means that only after 3 edited projections we get much more accurate point placement. For maximum accuracy edit more projections in more photos - if possible edit all the photos with projections where the target is visible. If the estimated projection seems perfect just press the approve button. After approving or moving projections they turn from estimated to manual - only these manual projections will be taken into account when calculating the 3D position of the point.

"drawing"

Now the yellow projection marker is right on the corner which is the target. Error in pixels should not exceed more than a few pixels. If that is the case we are ready to press ok. After pressing ok the position of the point in the dense cloud or on the DEM should adjust slightly. Repeat the process and place as many of these points as needed. Using snapping, the points can be easily connected by lines or polygons. Lines or polygons snapped to these accurate points will maintain accuracy and can be used to acquired more measurements.

Line

Line object is another layer used for measurements. In Pixpro line can have any amount of segments. Line object provides distance and angle measurements. As with points line measurements appear in the properties panel when the line in question is selected.

Line properties panel breakdown:

Properties


Name - name of the object

Points - Number of points in the line.

Ground truth checkmark - if checked, the line will stay in its current position even if the georeferencing of the whole project is changed. In other words lines' geographical coordinates will not change even if the whole project is georeferenced to a different geographical position. If this checkmark is not checked the line will always be tied to the 3D reconstruction and if the reconstruction is moved to a new geographical position by changing the georeferencing, the line will move along with the whole reconstruction and their geographical coordinates will change.

Color - Graphical color selection.

Lineweight - Graphical weight of the line. The higher the number the thicker the line will appear.

Line type - Either straight or draped. This determines how the lines is displayed graphically. It can be straight or draped over the DEM surface. This does not affect the measurements.

Calculations 2D


Horizontal length - total line distance in X and Y coordinate plane. In other words the total length of the line as seen from directly above. Any vertical (Z axis) point fluctuations will not have an impact on this measurement. Dense point cloud is sufficient to acquire this measurement.

"drawing"

In this example the 2-segement line is viewed directly from above. Surface being far from uniform has no influence when 2D Horizontal length is calculated. Its measured exactly as seen from above.

Vertical Length - vertical distance between the highest and the lowest points on the line. In other words the elevation difference between the lowest and the highest line vertices. Dense point cloud is sufficient to acquire this measurement.

Below and example of the same line but viewed from the side to better show the height fluctuation.

"drawing"

Calculations 3D


Surface Length - length of the line as it is projected on the DEM surface, in other words - a length of the profile that line creates. This measurement is best represented with just a draped line as in an example below.

"drawing"

Sightline Length - The shortest possible distance between points in 3D space. Direct sight length is calculated between each point in line and added up.

Slope angle - angle between the end points of the line. Angle is determined according to the gravitational plane of the project. If the first point of the line is directly above or below the second point - slope angle will be measured as 90 degrees. If both points are on the same plane, the angle will be measured as 0 degrees. All other situations should be measured between 0 and 90 degrees.

"drawing"

Elevation - elevation difference between the first and the end points of the line. Elevation is always expressed in a positive number.

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Lines also have their vertex projections which means they can be viewed edited in the same manner as points, although it is easier to make points using projections as described earlier and snap lines to those points. Nevertheless one can always double-click on any line object and examine or edit line projections. Same rule of at least 32 projections for each point (line vertex) applies. If less than 2 projections are manually edited, the line placement in the 3D space will not be affected. Below is an example of a simple 2 point line in the Edit Line window.

"drawing"

Please note that you can only edit one line point projection at a time. To select a different point on a line use the dropdown menu in the top - middle part of the window. This dropdown menu contains line name plus point number. Only the chosen point will be affected by projection changes.

Polygon

Polygons can be drawn in a few different ways:

  1. By using the Add polygon button "drawing" in the vertical toolbar.

  2. By pressing right mouse button on any of the existing line objects and choosing Create Polygon, which will connect the first and last line points and create a new polygon object in that way.

  3. By creating a single contour line and converting it to a polygon by pressing right mouse button on a single contour line in the layers panel and choosing create polygon.

Polygons are objects that are used for area and volume measurements. Polygon properties panel provides the user with extensive amount of information:

"drawing"

Properties


Name of the polygon - name of the selected polygon object.

Amount of points (vertices) that the polygon contains - vertices are points that connect the straight lines of polygon perimeter. Vertices also can be regarded as polygon corners.

Ground truth checkmark - if checked, the polygon will stay in its current position even if the georeferencing of the whole project is changed. In other words polygons' geographical coordinates will not change even if the whole project is georeferenced to a different geographical position. If this checkmark is not checked the polygon will always be tied to the 3D reconstruction and if the reconstruction is moved to a new geographical position by changing the georeferencing, the polygon will move along with the whole reconstruction and their geographical coordinates will change.

Polygon perimeter line color selection - allows changing the color of the polygon line. The fill color always stays the same.

Polygon perimeter line weight selection - allows changing the thickness of the polygon perimeter line. This only affects the depiction of the polygon, not measurements.

Polygon perimeter line type selection - allows changing the type of polygon perimeter. It can be either draped or straight. Straight line connects the polygon vertices directly while draped line follows the DEM surface (only DEM surface is supported). Example below.

"drawing"

Calculations 2D (XY plane) - used for area measurement


Calculated horizontal perimeter - calculated value of the polygon perimeter as projected to XY plane. In other words the polygon perimeter as seen directly from above. The actual surface of the DEM does not influence these calculations.

Calculated 2D area value - calculated value of the polygon area as projected to XY plane. In other words the polygon area as seen directly from above. The actual surface of the DEM does not influence these calculations.

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Calculations 3D - used for area and volume measurement


Calculated surface perimeter value - polygon perimeter calculation that follows the DEM surface along the perimeter line. By definition it should always be longer than 2D perimeter and its best represented as a draped line.

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Calculated sightline perimeter value - perimeter calculated using the shortest 3D distances between the polygon points. The surface of the DEM does not influence this calculation, only the position of the polygon points.

Calculated 3D area value - area of the DEM surface in the polygon. By definition always a larger value than 2D perimeter.

"drawing"

In volume measurements the base plane is a perfect surface which is perpendicular to the gravitational vector and its position greatly affects the volume measurements.

Calculated volume above the base plane - volume of the measured object above the chosen base plane.

Calculated volume below the base plane - volume of the measured object below the chosen base plane.

"drawing"

NOTE: If you see yellow exclamation marks near the measurements it means that the polygon might not be perfectly placed on the DEM. This usually occurs when different DEMs are swapped when keeping the same polygon. To makes sure that the polygon vertices are placed perfectly on the DEM surface, press right mouse button on the polygon in layers panel and click on "Project to DEM surface". The software will slightly adjust vertice position in the 3D space and volume measurements might be a little more accurate.

Base surface - greatly affects the volume measurements


In this section the user can choose the base plane for the selected polygon. Base planes are generated surfaces that greatly influence the volume measurements. In Pixpro there are 6 possible base plane options:

Fitted plane - also known as best fit. It is a flat surface that is generated while using all polygon point (vertex) data. Generally the recommended option for most measurement scenarios. (more detailed information on Base planes in the following chapter)

Max height plane - flat surface that is perpendicular to the gravitational vector at the highest point of the polygon selection. Exact height values are provided near the plane selection.

Mean height plane - flat surface at the mean height of the polygon selection points.

Min height plane - flat surface at the lowest height of the polygon selection points.

Custom height plane - flat surface at the user defined height.

Elevation model - base plane determined by another digital elevation map at the area of the polygon.

More detailed information on Base planes can be found in the Base planes and Timeline page.

Profile and Timeline


In this section profile "drawing" and timeline "drawing" buttons are used to open the profile and timeline panels. In case of a polygon the profile will show the cross-section of the polygon's perimeter.

Timeline button opens up a new panel in which timeline functionality can be used to compare volumes between different DEM's. To learn how to use the timeline go to Base planes and Timeline page.

Modeling


In this section we see 9 buttons used for either terrain leveling or DEM editing. To know more how these functions work see [6. Terrain editing] page. In the properties panel these buttons mean that to execute a particular function the selected polygon area will be used. Otherwise the functionality is identical to the tools from the toolbar.

Editing existing objects

To edit an existing object press right mouse button on any object type in layers panel. A slightly different menu for each object pops up and in turn user has different editing options for each type of object.

"drawing"

Point menu

Point editor - opens the point editor window in which you can edit point projections, coordinates and other options. This window should be already familiar as it is the same window in which projections are added/edited.

Rename Point - renames the point layer.

Edit Point Alt-E - this edit menu does not open any window but allows dragging the point to a new location.

Scope To Layer Object - navigates the 3D view to the selected object instantly.

Export point - exports the selected point. After selecting the export format Export Coordinate system dialog will require choosing the coordinate system.

"drawing"

Remove Point - deletes the point.

Line menu

Line editor - opens the line editor window. In this window line point (vertice) projections can be edited.

Rename Line - rename the line layer.

Add Point - allows adding additional points to the ends of the line. To add a point first select any end of the line and double-click on the place where another point should be added. Repeat this process as many times as necessary.

Edit Point - allows editing existing point locations of the line. To edit a point just click and drag the point which needs to be edited.

Delete Point - deletes any point of the line.

Insert Point - inserts a new point at the selected place. Line is connected automatically to the newly inserted point.

Create Polygon - closes the line to create a polygon. First and the last line points are automatically connected in the process.

Scope To Layer Object - navigates the 3D view to the selected object instantly.

Export Line - exports line using the selected format. .dxf .shp .pxg formats are available for export.

Remove Line - deletes the line object.

Polygon menu

Polygon Editor - opens the polygon editor window that can be used to edit polygon point projections. Windows works identically to those of point and line.

Rename Polygon - renames the polygon.

Edit Point - allows moving polygon points to change the shape of the polygon.

Delete Point - deletes any polygon point. To delete a point just click on it.

Insert Point - allows inserting new point into the polygon. To insert a new point simply click where the new point should be inserted.

Scope To Layer Object - navigates the 3D view to the selected object instantly.

Show Timeline - opens the timeline panel.

Project to DEM surface - project the polygon to the surface for maximum measurement accuracy.

Export Polygon - exports polygon in selected format.

Remove Polygon - deletes the polygon.

Measurement examples

theoretically anything that has been scanned can be measured. It is only a matter of the purpose of the scan and imagination. Below a few measurement examples.

Free standing piles of material:

"drawing"

Roof or ground areas:

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Road section length:

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Wire sag height:

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Slope angle:

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