PS_1.0.0 -Tutorial (BL) - Orthophoto, DEM (with GCP)

First run tutorial: Orthophoto and DEM Generation with Agisoft PhotoScan Pro 1.0.0 (with Ground Control Points) PhotoScan Preferences Open PhotoScan P...

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First run tutorial: Orthophoto and DEM Generation with Agisoft PhotoScan Pro 1.0.0 (with Ground Control Points) PhotoScan Preferences Open PhotoScan Preferences dialog from Tools menu using corresponding command.

Set the following values for the parameters in the General tab: Stereo Mode: Disabled Stereo Parallax: 1.0 Write log to file: specify directory where Agisoft PhotoScan log would be stored (in case of contacting the software support team it could be required) Set the parameters in the OpenCL tab as following: Check on any OpenCL devices detected by PhotoScan in the dialog and reduce the number of active CPU cores by one for each OpenCL device enabled. Set the following values for the parameters in the Advanced tab: Project compression level: 6 Keep depth maps: enbled Store absolute image paths: disabled Check for updates on program startup: enabled Enable VBO support: disabled

Add Photos To add photos select Add Photos... command from the Workflow menu or click Add Photos button located on Workspace toolbar. In the Add Photos dialog browse the source folder and select files to be processed. Click Open button.

Load Camera Positions At this step coordinate system for the future model is set using camera positions. Note: If camera positions are unknown this step could be skipped. The align photos procedure, however, would take more time in this case. Open Ground Control pane using the corresponding command from the View menu. Click Import button on the Ground Control pane toolbar and select file containing camera positions information in the Open dialog. The easiest way is to load simple character-separated file (*.txt) that contains x- and ycoordinates and height for each camera position (camera orientation data, i.e. pitch, roll and yaw values, could also be imported, but the data is not obligatory). In Import CSV dialog indicate the delimiter according to the structure of the loading file and select the row to start loading from. Note that # character indicates a commented line that is not counted while numbering the rows. Indicate for the program what parameter is specified in each column through setting correct column numbers in the Columns section of the dialog. Check your settings in the sample data field in Import CSV dialog.

Click Open button. The data will be loaded into the Ground Control pane. Import EXIF Ground Control pane toolbar button can also be used to load camera positions information if EXIF meta-data is available. Then click on the Settings button in the Ground Control pane and in the Ground Control Settings dialog select corresponding coordinate system from the list.

Click OK and camera positions will be marked in Model View using their geographical coordinates:

Align Photos At this stage PhotoScan refines the camera position for each photo and builds the point cloud model. Select Align Photos command from the Workflow menu.

Set the following recommended values for the parameters in the Align Photos dialog: Accuracy: High (lower accuracy setting can be used to get the rough camera positions in the shorter time) Pair preselection: Ground Control (in case camera positions are unknown Generic preselection mode can be used) Constrain features by mask: Disabled (Enabled in case any areas has been masked prior to processing) Point limit: 40000 Click OK button to start photo alignment.

Place Markers Markers are used to optimize camera positions and orientation data, which allows for better model reconstruction results. To generate accurate orthophoto at least 10 – 15 ground control points (GCP) should be distributed evenly within the area of interest to be processed. To be able to follow guided marker placement approach (that would be faster and easier) you need to reconstruct geometry first. Select Build Mesh command from the Workflow menu and specify following parameters in the Build Mesh dialog:

Click OK button. Then, when the geometry is built (it usually takes a few seconds to reconstruct mesh based on the sparse point cloud), open a photo where a GCP is visible in Photo View by double-clicking on its icon in the Photo pane. Zoom in to locate the GCP on the photo and place a marker in the corresponding point of the image using Create Marker command from the photo context menu available on right-click on the opened photo in the corresponding position:

Select the marker on the Ground Control pane. Then filter images in Photos pane using Filter by Markers option in the context menu available by right-clicking on the markers label in the Workspace pane.

Now you need to check the marker location on every related photo and refine its position if necessary to provide maximum accuracy. Open each photo where the created marker is visible. Zoom in and drag the marker to the correct location while holding left mouse button. Repeat the described step for every GCP.

Input Marker Coordinates Finally, import marker coordinates from a file. Click Import button on the Ground Control pane toolbar and select file containing GCP coordinates data in the Open dialog. The easiest way is to load simple character-separated file (*.txt) that contain markers name, x-, y- coordinates and height.

In Import CSV dialog indicate the delimiter according to the structure of the file and select the row to start loading from. Note that # character indicates a commented line that is not counted while numbering the rows. Indicate for the program what parameter is specified in each column through setting correct column numbers in the Columns section of the dialog. Check your settings in the sample data field in Import CSV dialog:

Click OK button. The data will be loaded into the Ground Control pane.

Optimize Camera Alignment To achieve higher accuracy in calculating camera external and internal parameters and to correct possible distortion (e.g. “bowl effect” and etc.) optimization procedure should be run. This step is especially recommended if the ground control point coordinates are known almost precisely (several centimeters accuracy) (marker based optimization procedure). Click the Settings button in the Ground Control pane and in the Ground Control Settings dialog select corresponding coordinate system from the list according to the GCP coordinates data. Set the following values for the parameters in Measurement accuracy section:

Camera accuracy: 10 Marker accuracy: 0.005 (The marker accuracy is recommended to be set at 0 value if the real marker accuracy is within 0.02 m. In this case PhotoScan will assume that markers coordinates are known exactly, which can help to obtain more accurate results.) Scale bar accuracy: 0.001 Projection accuracy: 0.1 Tie point accuracy: 4 Click OK button. On the Ground Control pane uncheck all photos and check the markers to be used in optimization procedure. The rest of the markers that are not taken into account can serve as control points to evaluate the optimization results. Click Optimize button on the Ground Control pane toolbar.

Select camera parameters you would like to optimize. Click OK button to start optimization process.

Set Bounding Box Bounding box is resizable and rotatable with the help of Region tools from the Toolbar.

Resize Region and

Rotate

Important: The red-colored side of the bounding box indicates the plane that would be treated as ground plane and has to be set under the model.

Build Dense Point Cloud Based on the estimated camera positions the program calculates depth information for each camera to be combined into a single dense point cloud. Select Build Dense Cloud command from the Workflow menu.

Set the following recommended values for the parameters in the Build Dense Cloud dialog: Quality: Medium (higher quality takes quite a long time and demands more computational resources, lower quality can be used for fast processing) Depth filtering: Aggressive (if the geometry of the scene to be reconstructed is complex with numerous small details or untextured surfaces, like roofs, it is recommended to set Mild depth filtering mode, for important features not to be sorted out)

Points from the dense cloud can be removed with the help of selection tools and Delete/Crop instruments located on the Toolbar.

Build Mesh After dense point cloud has been reconstructed it is possible to generate polygonal mesh model based on the dense cloud data. Select Build Mesh command from the Workflow menu.

Set the following recommended values for the parameters in the Build Mesh dialog: Surface type: Height Field Source data: Dense cloud Polygon count: Medium (maximum number of faces in the resulting model. The values indicated next to High/Medium/Low preset labels are based on the number of points in the dense cloud) Interpolation: Enabled Click OK button to start mesh reconstruction.

Edit Geometry Sometimes it is necessary to edit geometry before building texture atlas and exporting the model. Unwanted faces could be removed from the model. Firstly, you need to indicate the faces to be deleted using selection tools from the toolbar. Selected areas are highlighted with red color in the Model View. Then, to remove the selection use Delete Selection button on the Toolbar (or DEL key) or use Crop Selection button on the Toolbar to remove all but selected faces. If the overlap of the original images was not sufficient, it may be required to use Close Holes command from the Tools menu at geometry editing stage to produced holeless model. In Close Holes dialog select the size of the largest hole to be closed (in percentage of the total model size).

PhotoScan tends to produce 3D models with excessive geometry resolution. That's why it is recommended to decimate mesh before exporting it to a different editing tool to avoid performance decrease of the external program. To decimate 3D model select Decimate Mesh... command from the Tools menu. In the Decimate Mesh dialog specify the target number of faces that should remain in the final model. For PDF export task or web-viewer upload it is recommended to downsize the number of faces to 100,000-200,000.

Click OK button to start mesh decimation procedure.

Build Texture This step is not really needed in the orthophoto export workflow, but it might be necessary to inspect a textured model before exporting it or it might be useful for precise marker placement. Select Build Texture command from the Workflow menu.

Set the following recommended values for the parameters in the Build Texture dialog: Mapping mode: Orthophoto Blending mode: Mosaic Texture size/count: 8192 (width & height of the texture atlas in pixels) Enable color correction: disabled (the feature is useful for processing of data sets with extreme brightness variation, but for general case it could be left unchecked to save the processing time) Click OK button to start texture generation.

Generate Orthophoto Select Export Orthophoto → Export JPEG/TIFF/PNG command from File menu.

Set the following recommended values for the parameters in the Export Orthophoto dialog: Projection type: Geographic Projection: by default the projection set in the Ground Control Settings is used Blending mode: Mosaic Enable color correction: disabled (the feature is useful for processing of data sets with extreme brightness variation, but for general case it could be left unchecked to save the processing time) Pixel size: maximum effective resolution is shown by default Split in blocks: 10000 x 10000 (if the exported area is large it is recommended to enable Split in Blocks feature, since the memory consumption is rather high at exporting stage) Region: set the boundaries of the model's part that should be projected and presented as orthophoto. Click Export... button and then specify target file name and select type of the exported file (e.g. GeoTIFF). Click Save button to start orthophoto generation.

Generate DEM Select Export DEM → Export GeoTIFF/BIL/XYZ command from File menu.

Set the following recommended values for the parameters in the Export DEM dialog: Projection type: Geographic Projection: by default the projection set in the Ground Control Settings is used Crop invalid DEM: check this option to crop the regions with unreliable elevation data, since they are visible on less than two source photos Pixel size: you can increase the effective resolution compared to the default value Split in blocks: 10000 x 10000 (if the exported area is large it is recommended to enable Split in blocks feature, since the memory consumption is rather high at exporting stage) Region: set the boundaries of the model's part that should be presented as DEM. Click Export... button and then specify target file name and select type of the exported file (e.g. GeoTIFF). Click Save button to start DEM generation.

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