B. Image Measurement

2D positions on the image can be measured be activating the Digitise icon on the toolbar. When the cursor passes over an image it will change to a cross-hair indicating that Measurement mode is active. There are 8 3D ground control points available, thus we need to measure their 2D image position by digitising.

Location of Ground Control Points

Ground Control Points in WGS84 Geographic coordinates
(Lat, Long in decimal degrees; Height in metres)

Lat: -37.83763402
Long: 144.9233028
Height: 7.468966269

|

Lat: -37.83761557
Long: 144.9233056
Height: 7.492171614

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Lat: -37.83948301
Long: 144.9274518
Height: 6.61049404 |
Lat: -37.83241951
Long: 144.912129
Height: 8.266415111

Lat: -37.84130826
Long: 144.9380619
Height: 8.002016879 |
Lat: -37.8406592
Long: 144.9369441
Height: 8.205101524

Lat: -37.8402606
Long: 144.9312094
Height: 6.702512649 |
Lat: -37.82682903
Long: 144.9116066
Height: 7.568104496

1. Approximate positions of Control Points (only available when RPCs are provided)

Right-Click XYZ Point Node > 3D to 2D > With RPC > Choose Image (StereoPanP001).

This will reproject the positions of the control points onto the image. They should now appear on the image labelled in yellow. In the Items window, Right-Click on the 3Dto2DwithRPC node > Set/Unset Active will enable and disable the display.

It is important to remember that in this case, the reprojection uses the RPC sensor model and hence these positions are only as accurate as the vendor-provided RPCs. Therefore, we use the reprojected positions only as a guide to approximately locate the control points in order for further precise manual measurement of the points.

2. Digitising Points

Open StereoPanP001 image by Double-Click on its thumbnail in the Items Window. Activate the Digitise icon and begin measuring ground control points by Left-Click on the mouse. As you digitise, all the 2D positions will be stored in a 2DPoints node which is accessible under its corresponding Image node. Double-Click on the 2DPoints node will maximise the coordinate display into the main window. Here you can edit the labels, delete points, change sigmas and calculate best-fit ellipses. Alternatively, Pressing the L-key will set the label name for the next digitised point. Pressing the CTRL-key during digitising will activate a zoom-in box for the region surrounding the cursor, enabling precise measurement

Use this method to digitise BASA and BASB.

3. Digitising Centroids

The remaining ground control points, BEACON, COOK, NOT, STO, SWA and TODD are the centroids of road round-abouts. The positions of these points can be determined by digitising the circumference of the feature, then calculating a best-fit ellipse.

After digitising the circumference of the feature, unselect the Digitise icon so that the cursor now appears as a pointer. Define a region of interest (ROI) around the digitised circumference points by dragging the cursor around all points to be used in the least-squares best-fit calculation. The ROI border should appear in blue. Right-Click within the ROI > Ellipse-fitting. Give the ellipse the name of the control point you are measuring.

The ellipse will be stored in a XYEllipses node and the 2D position of the centroid of the round about will now be appended to the 2D points node. Remove the 2D circumference points from 2D point list by Right-Click > Delete Point(s), as they are no longer needed.

Use this method to digitise BEACON, COOK, NOT, STO, SWA and TODD.

Digitise Ellipse Centroids eg. COOK

a. Approximate location of COOK:
Reprojected using vendor RPCs

|

b. Digitised circumference points
of COOK

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c. Region of Interest and Ellipse Fitting |
d. Ellipse Fitting result

e. Precise location of COOK |

The sigma values SX and SY can be changed by Right-Click on the 2D point node. Change the sigma values to a third of a pixel, 0.3.

4. Exporting 2D points

The 2D points can be exported by Right-Click on the 2D node in the Items window. Export options include a space or comma separated file. This allows easy import into another Barista project or into another software package.

The entire process should be repeated for all images and ground control points.

A. Project setup
C. Sensor Orientation
D. Monoplotting
E. Orthoimage generation
F. Pansharpening

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