Software Workflow

AgiSoft PhotoScan Pro 0.9.0

For use with Gatewing X100 UAS

©2012 Gatewing.

The material contained in this document is confidential and intended for use only by parties authorized by Gatewing.

All rights reserved. No part of this document may be photocopied, reproduced, stored in a retrieval system, or transmitted, in any form or by any means whether, electronic, mechanical, or otherwise without the prior written permission of Gatewing.

Gatewing Buchtenstraat 9/1 9051 Gent, Belgium

Tel: +32 9 335 05 15 www.gatewing.com Fax: +32 9 335 88 03 Mail: documentation@gatewing.com

CONTENTS

Workflow for X100 image processing in Agisoft PhotoScan Pro 0.9.0 .................................. 4

1.1 Important remarks ............................................................................................................................... 4

1.2 Project processing .............................................................................................................................. 4

1.2.1 PhotoScan settings ........................................................................................................................ 4

1.2.2 Open project .................................................................................................................................. 6

1.2.3 Importing GCPs ............................................................................................................................. 7

1.2.4 Align photos ................................................................................................................................... 9

1.2.5 Indicate GCPs .............................................................................................................................. 10

1.2.6 Optimize alignment ...................................................................................................................... 11

1.2.7 Build geometry ............................................................................................................................. 13

1.2.8 Export products ............................................................................................................................ 14

1.3 Merging multiple flights in one project ........................................................................................... 17

1.4 Troubleshooting ................................................................................................................................ 18

1.4.1 Processing capabilities ................................................................................................................ 18

1.4.2 Align photos ................................................................................................................................. 18

1.4.3 Optimize ....................................................................................................................................... 19

1.4.4 Build geometry ............................................................................................................................. 19

1.4.5 Export products ............................................................................................................................ 20

1 Workflow for X100 image processing in

Agisoft PhotoScan Pro 0.9.0

1.1 Important remarks

The workflow described below is specifically written for Agisoft PhotoScan 0.9.0, which is the latest official release. Projects saved in PhotoScan 0.8.5 or earlier can be opened in 0.9.0 but not vice versa. As indicating GCPs has greatly improved in PhotoScan 0.9.0, there is only a single document containing one workflow for projects both with and without GCPs. As a result, you can start this document at 1.2.1, continue to 1.2.2 and so on. Where steps should be skipped if you don’t have GCPs, this is mentioned.

1.2 Project processing

1.2.1 PhotoScan settings

When launching PhotoScan for the first time, some settings need to be adjusted to optimize performance. These settings need to be done only once, at the first use of PhotoScan, and are loaded by default in subsequent sessions. If you already have checked the settings earlier, start your workflow from 1.2.2 (regardless of the availability of GCPs).

In the menu bar, go to Tools -> Camera Calibration…. Set the Calibration mode to Groups (this can only be done when a project is already loaded).

− 5 −

In the menu bar, go to Tools -> Preferences….

• General tab

� Photo alignment: Maximum points per photo: leave at default (40000) � Depth filtering: leave at default (aggressive) but see Troubleshooting � Select “Write log to file” and click “…”: browse to a generic directory (such as

C:\Users\User\Documents\PhotoScanlog or a directory under any other available hard disk partition) and name the file [gatewingaccountname]_PhotoScanlog.txt. Processing logs will be added to the text file without overwriting previous sessions. If you require support from Gatewing or Agisoft, please attach this file to your communication.

� Enable VBO support: check this if you have an OpenCL-enabled GPU from NVIDIA. Leave it unchecked if you have a GPU from another mark (this applies to any Mac). Refer to the Console pane in PhotoScan (which can be toggled in the View menu) to see your mark and type of GPU.

� Leave the other options at their default settings.

• OpenCL tab: if an OpenCL-supporting graphics card (GPU) is detected on your machine, it will be displayed under OpenCL devices. In that case, enable it by clicking the check box next to it, and reduce the number of active CPU cores by 1 for each enabled GPU (with “GPU” referring to a physical graphics card listed next to a checkbox, not the number of GPU “cores” or pipelines displayed for that GPU. Thus, unless you have a dual graphics card in your workstation, you need to take 1 GPU into account). If your CPU supports hyper-threading (e.g., if 8 active CPU cores are displayed when you have a quad core i7), disable two active CPU cores for each enabled GPU. If an Open-CL-enabled GPU is not present, all CPU cores should be activated to achieve the highest processing speed.

− 6 −

1.2.2 Open project

In the menu bar, go to File -> Open… or click the Open icon on the toolbar. Browse to the projectname.psz file generated from the Stretchout opening screen (by choosing PhotoScan (psz) from the dropdown list under PRO processing) and click Open. The project can also be opened in PhotoScan by directly clicking the link to the created project file in the toolbar of the Stretchout opening screen. Your project will be loaded with the photos and corresponding GPS positions of the cameras. In the main Model window, you will see camera positions represented by blue dots. The corresponding image name will show up when zooming in. Selecting a photo by left-clicking it in the image list in the workspace Overview pane or in the photo pane will highlight the corresponding position in the main model window and the photo can be opened in a tab in the Model window by double-clicking. You can zoom in and out on the Model window by using the mouse scroll wheel and rotate it by clicking and holding the left mouse button (when the mouse is placed directly over one of the axes on the trackball, the axis will be highlighted and the view can be rotated over that specific axis). The model can be panned relative to the trackball center by clicking and holding the right mouse button (when panning in the single photo tab, click and hold the left mouse button). The different window panes can be toggled on and off from the View menu and dragged and dropped around the window to customize the user interface.

− 7 −

1.2.3 Importing GCPs

If you have ground control points (GCPs) available for your project, you can import the coordinate file now. First, the camera coordinates need to be converted to the datum and coordinate system of the GCPs. In the Ground Control pane (to open the pane if it’s not visible, go to View in the menu bar and enable Ground Control), select all photos by clicking one and typing Ctrl-a (or by

clicking the first and holding Shift while clicking the last) and click Convert in the Ground Control pane toolbar. Select the desired datum and coordinate system from the dropdown list: click More… to select the system from the tree list, filter by EPSG code or name (case sensitive!)

in the search box or load a .prj file from the Load icon if the coordinate system is not in the shortlist of earlier used systems.

− 8 −

Next, click Import on the Ground Control pane toolbar. Browse for your GCP file in any Character separated values format with .txt extension and click Open. Specify the relevant delimiter and change the order of the columns to import if necessary. Make sure that the import is set to start at row 0 if no header is present in the file. Check the preview of the import shown at the bottom of the Import CSV dialogue box and click OK. Click “yes to all” to create all the GCP markers (or click “yes” or “no” individually if you only need some of the GCP identifiers in your text file). The markers will appear below the image acquisition center icons in the 3D Model pane. Indicating the GCPs on the images is done after the next step.

− 9 −

1.2.4 Align photos

In the menu bar, go to Workflow -> Align photos…

You have the option of doing a rapid processing, greatly saving on computing time by reducing the accuracy of the alignment, or to do a production quality processing which requires more time and processing power in favor of a high accuracy alignment. The reduction of the processing time in the alignment for rapid processing is achieved by limiting the number of feature points detected and matched, and hence reducing the density of the initial (sparse) point cloud.

• For rapid processing: Accuracy = Low, Pair Selection = Ground Control, click OK. Afterwards,

click Save in the toolbar.

• For production quality processing: Accuracy = High, Pair Selection = Ground Control, click

OK. Afterwards, click Save in the toolbar.

After alignment, a sparse 3D point cloud can be seen in the main model window, and the reconstructed camera positions are now represented by a black vector line with a blue rectangle at its end, visualizing the camera sensor orientation. The corresponding image name is displayed, but the blue dot representing the initial position has disappeared (unless PhotoScan

− 10 −

failed to align an image due to bad overlap or low texture). You can disable the camera position

plots by toggling the Show Cameras button on the toolbar.

1.2.5 Indicate GCPs

This step can be skipped if you’re processing a project without ground control points. In the ground control pane, select a GCP (click the entry once so it is highlighted in blue). In the Photos

pane, click Filter by markers to see only the images in which the currently selected GCP is probably visible. Open an image by double clicking the thumbnail; it will open in a tab next to the

Model pane. The GCP will appear as a grey icon . By enabling the Edit Markers mode on

the toolbar, the GCP marker icon’s base dot will turn red when you hover the mouse pointer over the marker. You can now drag the marker to the correct measurement position. At that

point, the marker will appear as a green flag , meaning it is enabled and will be used for further processing. Double click to open the next photo; the view will be automatically centered and zoomed to the marker and the position will be already better estimated (you can further zoom in with the mouse scroll wheel or drag the image by clicking and holding the left mouse button). Drag the marker to the correct position. You need to do this on at least two images in order to include the corresponding GCP for further processing. You may continue by double clicking the next image; as soon as the GCP marker position has already been indicated on at

− 11 −

two images, the proposed position will almost exactly match the point of measurement. You can now slightly drag the marker to enable it (turning it into a green flag) or leave it unchanged (grey marker icon) to exclude it from processing. If you have enabled a marker which you want to disable again, right-click it and choose Clear Marker. We recommend indicating the marker position only on sharp images. When you have indicated all the marker positions for a certain GCP, select the next GCP entry and repeat the process. Mathematically, you need to indicate marker positions for at least 3 GCPs. Accurate error estimates can be calculated with at least 4 GCPs, while often at least 5 are needed to cover the center of the project as well, which reduces the chance of error propagation and resulting terrain distortions especially on flat or undulating terrain types. Using at least 10 GCPs can further increase the accuracy significantly, with markers spread around the project in x, y and z, also covering the center of the project.

1.2.6 Optimize alignment

First, the sparse point cloud resulting from the alignment needs to be checked for points with a high reprojection error and outliers (points outside the bounding box are not taken into account).

Outlier points can be manually removed by selecting them using the , or selection

tools (selected points will turn pink) and clicking Delete selection from the toolbar (or pressing delete). Also, points with a high reprojection error can be selected by going to Edit -> Gradual Selection… and moving the slider to set the desired reprojection error threshold (expressed in pixels) above which all the points are selected (remark that the slider bar orientation is in that respect somewhat counter-intuitive). Generally, a threshold of 1 pixel is desirable, but make sure that not too many points are selected (you can see the number of selected points in the lower left corner of the main Model window – it is a good idea to keep this number within 10% (or 20% at most) of the total number of points). When a project contains rather dark or blurred images or images with an otherwise difficult texture, or if you aligned the project at lower accuracy settings, it may be necessary to set the threshold at 2 or 3 pixels in order to keep the amount of selected points within a reasonable limit. The points selected in this way will turn pink in the model

overview and can be removed by clicking Delete selection from the toolbar. From the same Gradual Selection window, the criterion can also be set to Reconstruction uncertainty. This is expressed as a value without dimension, and is related to the degrees of freedom in the 3D reconstruction which is in turn related to the directional overlap in the photos (typically, points along the edges of the project and in steep valleys have a high reconstruction uncertainty because they were visible only on forward overlapping photos, but are lacking sideward overlap). Deleting points with a high reconstruction uncertainty can be done optionally, as the effect on the optimization accuracy will be only minor. Through user experience, we have seen that a threshold set at 10 is usually a good starting point, but take care not to select too many points. The points selected in this way will turn pink in the model overview and can be removed by

clicking Delete selection from the toolbar.

− 12 −

Best results are obtained when the alignment is first optimized based on the camera coordinates only, and a second time based on the GCP coordinates only if GCPs are available. In the Ground Control pane, disable all the GCP Marker coordinates first by selecting one and pressing Ctrl-a,

right-click and choose Uncheck. Click Settings in the Ground Control toolbar: set Camera

accuracy (m) = 1, leave the rest at default values, click OK. Next, click Optimize in the Ground Control toolbar: leave all options at the default (all enabled) en click OK. If you don’t have GCPs for your project, the optimization ends here and you can proceed to 1.2.8. If you do have GCPs, select all of the photos in the Ground Control pane, right-click and choose Uncheck. Then,

select all of the Markers, right-click and choose Check. Go to Settings in the Ground Control toolbar: leave Camera accuracy unchanged (since all image GPS positions have now been disabled, this setting doesn’t play a role anymore); set Marker accuracy to one order of magnitude tighter than the average accuracy of the GCP measurements: for instance, this would be 0.001m for GCPs measured with RTK GPS (centimeter accuracy); leave the rest at default

values, click OK. Next, click Optimize in the Ground Control toolbar: leave all options at the default (all enabled) and click OK. Verify that the average error and error in x, y and z displayed at the bottom of the GCP Marker coordinates list ends up in an acceptable range (within 1-2 times the nominally expected GSD in x and y and 2-3 times in z, although generally it will be

lower) and click Close (to see errors in the Ground Control pane, click the View Errors button

in the Ground Control toolbar). Click Save in the toolbar.

− 13 −

1.2.7 Build geometry

In the menu bar, go to Workflow -> Build Geometry…

Before starting the Build Geometry step it is recommended to check the bounding box of the reconstruction volume to make sure that it includes the whole region of interest (in all dimensions). The bounding box should not be too large also, as this can lead to an increased processing time and memory requirements. The bounding box can be adjusted using the Resize

Region and the Rotate Region tool from the toolbar.

You have the option of doing a rapid processing, greatly saving on computing time by reducing the quality and level of detail in the geometry reconstruction, or to do a full processing which requires much more time and processing power in favor of a highly detailed geometry with less noise in the DSM. Reducing the processing time for a rapid reconstruction is achieved by generating a mesh based on the sparse point cloud generated in the alignment, without a further densification of the 3D point cloud.

• For rapid processing: Object type = Height field, Geometry Type = Point Cloud, Face count =

200,000, Filter threshold = 0, click OK. Afterwards, click Save in the toolbar.

• For full processing: Object type = Height field; Geometry type = Smooth, Target Quality = Medium (will downsample the images to get a 3D coordinate every 4 pixels; typically takes several hours but will give acceptable results for most cases), High (will downsample the images to get a 3D coordinate every 2 pixels; typically takes >10-20 hours) or Ultra high (will calculate a 3D coordinate for every pixel in original imagery; may take more than a day or several days) – refer to Troubleshooting to take the RAM size requirements for the different target qualities with respect to the number of images into consideration; Face count = 0 or anything from 10,000,000 to 2,000,000,000. Face count set at “0” means that PhotoScan will determine an optimum number of faces (note that the meaning of “0” faces differs from PhotoScan 0.8.5!), but this may not be enough to describe all the features on your terrain.

− 14 −

PhotoScan is theoretically able to calculate up to 2bn faces, which is the number you should set if you want the software to calculate the maximum achievable number of faces for your project (corresponding to the “0” setting in PhotoScan 0.8.5). While in most cases this will yield a model with around 50M faces, it may also create a model with over 200M faces depending on your terrain texture. Please note that in the latter case, your GPU is likely to fail

in visualizing the model (see Troubleshooting). Afterwards, click Save in the toolbar.

1.2.8 Export products

Orthomosaic

In the menu bar, go to File -> Export Orthophoto > -> Export JPEG/TIFF/PNG… A progress window is displayed during the calculation of the resolution, after which a dialogue box opens.

• Projection Type = geographic (default); Datum = the datum of your GCPs by default or World Geodetic System 1984, Coordinate system = the coordinate system of your GCPs by default or change to the appropriate WGS 84/UTM zone in which the project is located if you don’t have GCPs; Write KML file (footprint) and World file (.tfw) = check if desired (if left unchecked, georeferencing information will still be contained in the GeoTIFF .tif file); Blending mode = Mosaic; Fill holes = checked; Pixel size: fill out the desired resolution with equal numbers for H and V (in meters). If you specify a higher resolution than the calculated average GSD as shown by default (for instance by filling out 0.01m for a flying height of 150m that would normally result in an expected GSD of 0.05m), pixel colors will be artificially interpolated. If you specify a lower resolution (e.g. 0.2m), the orthomosaic will be downsampled. Leave the rest unchecked or fill out as desired (for instance, the orthomosaic can be split in blocks of fixed pixel dimensions to limit file size) and click Export…

• Fill out the desired name (such as projectname_ortho5cm_UTM31N) and save as type TIFF/GeoTIFF (*.tif), click Save.

− 15 −

DEM

In the menu bar, go to File -> Export DEM… This export option allows you to generate gridded products based on the triangular mesh. A progress window is displayed during the calculation of the resolution, after which a dialogue box opens.

• Projection Type = geographic (default); Datum = the datum of your GCPs by default or World Geodetic System 1984, Coordinate system = the coordinate system of your GCPs by default or change to the appropriate WGS 84/UTM zone in which the project is located if you don’t have GCPs; Write KML file (footprint) and World file (.tfw) = check if desired (if left unchecked, georeferencing information will still be contained in the GeoTIFF .tif file); Crop invalid DEM = checked; Pixel size: fill out the desired resolution with equal numbers for H and V (in meters). Note that the default value corresponds to the resolution at which the dense 3D was calculated based on the Target Quality setting (i.e. Medium will yield a resolution of 4x the Ortho default value). You can set a higher value to match the Ortho resolution, in which case additional grid cell elevation values will be interpolated. Leave the rest unchecked or fill out as desired (for instance, the DEM can be split in blocks of fixed pixel dimensions to limit file size) and click Export…

• Fill out the desired name (such as projectname_dem5cm_UTM31N) and save as type TIFF/GeoTIFF (*.tif), XYZ text file (.xyz) or ArcInfo ASCII grid text file (.asc); click Save.

Processing report

The processing report is automatically generated and contains a thumbnail of the orthomosaic and DEM, along with processing statistics such as an indication of image overlap, number of 3D

− 16 −

points, reprojection error, residual errors etc. In the menu bar, go to File -> Generate Report… and specify the name and location to store the .pdf file.

Optional: point cloud

In the menu bar, go to File -> Export Points… This option allows you to export the irregular sparse (as displayed in the 3D Model window) or dense (as calculated during the Build Geometry step) 3D point cloud. Please note that the dense point cloud will differ significantly from the DEM export, as no filtering is applied and outlier points as well as significant noise in z will be included. Filtering and smoothing in external software is usually required to make this file meaningful. There is currently also no option to split this file in blocks, and the file size may make it unmanageable for many software packages (at Medium quality, typically > 10GB). First, specify a name (such as projectname_xyzpointcloud_coordsystem), and choose a file format (XYZ point cloud text file .txt or ASPRS text file .las); click Save. Next, choose the desired coordinate system, leave the Shift at 0, choose whether Point colors and normal should also be included as additional fields in the text file, and set the number of decimals to be exported (this can be decreased to 2 or 3 corresponding to cm or mm precision to reduce the file size). When you have chosen XYZ.txt as a file format, you can only export the sparse 3D point cloud as generated after the alignment and visualized in the 3D Model view: the Quality setting is disabled. When you have chosen ASPRS.las as a file format, you can export the dense point cloud by setting the Quality to the corresponding quality used in the Build Geometry step (mostly Medium). If you choose a higher Quality setting than the one used in Build Geometry, export time will increase significantly as an additional dense matching is done in the background.

Optional: residual errors, calculated camera parameters and rectified images

An overview of ground control coordinates and residual errors along with interior and exterior

camera position and orientation can be exported by clicking the Export toolbar button in the Ground Control pane. Specify the file name and format type (usually as Character-separated values in a .txt text file) and click Save. Next, specify the delimiter and what information to include in the export (always check residual errors); click OK. If you require camera orientations to be expressed as Omega Phi Kappa (OPK) rather than Yaw Pitch Roll (YPR), go to the Tools menu -> Export -> Export Cameras…. Set the export format to Omega Phi Kappa (.txt). Set the desired coordinate system and click OK.

− 17 −

Camera calibration (interior orientation) parameters can be viewed and exported from the Tools menu -> Camera Calibration… In the dialogue box, make sure the radio button next to Refined is checked. Select a random photo (if your project contains multiple flights, make sure to select a photo from each flight by holding Ctrl while clicking to select multiple entries) and click Export…. Select a file name; the parameters are stored by default in a .xml text file; click Save. With the Calibration mode set to Groups, PhotoScan calculates the same reconstruction parameters for all images aligned together, but values may differ for photos belonging to multiple flights as the camera geometry has likely changed between flights.

Individual images corrected for lens distortions can be exported from the Tools menu -> Export -> Undistort Photos…. These images can be used in external software for mosaicking and seamline editing.

1.3 Merging multiple flights in one project

Generally, it is preferable to process as many images as possible in a single chunk during processing, since making use of more data points will result in higher overall accuracies.

− 18 −

However, if the number of images from multiple flights to be processed as one block exceeds the hardware requirements for a given reconstruction quality (see Troubleshooting), you have to split the project in multiple chunks. In that case, make sure your flights (or chunks) have enough GCPs to be processed individually with GCPs to get the best results.

In the Stretchout opening screen, add each individual flight and export each flight to a PhotoScan .psz file. Open one of the flights in PhotoScan, go to File in the menu bar and choose Append… Browse to the location of the .psz file of one of the other flights and click Open. The flight will be added in a separate Chunk in the Workspace pane.

For processing in a single chunk: expand the other chunks, select all of the photos and drag and drop to the first chunk. You can delete the empty chunks afterwards. Proceed from 1.2.3 in the workflow described above.

For processing as multiple chunks to be merged afterwards, all chunks need to be individually aligned first (this can be facilitated by choosing Batch Process… from the Workflow menu and click Add… to specify the job type: select Align Photos and apply to All Chunks. Change the Alignment settings by double-clicking on the values and selecting the correct ones from the drop down list (see above). Make sure to enable Save project after each step and click OK. The alignments of each Chunk also need to be individually optimized. This cannot be done from the Batch Process… module. To activate an individual Chunk, double-click it in the Workspace pane (it will turn bold) and perform the Optimize alignment as described above under 1.2.6 (of course, steps 1.2.3 and 1.2.5 should also be done for each of the chunks). Repeat this for each chunk. Finally, go to Workflow in the menu bar and choose Merge Chunks… Select the flights (chunks) to be merged and enable Merge models and Merge markers before clicking OK. Afterwards, the build geometry and the rest of the workflow can be resumed from 1.2.7 as described above.

1.4 Troubleshooting

1.4.1 Processing capabilities

The CPU and GPU architecture of your machine determines the processing speed of your projects. Older or entry-level CPU’s or the lack of an OpenCL-enabled GPU will result in longer processing times, but should not result in processing failures.

The amount of RAM memory available determines the size of the projects that can be processed, and/or the accuracy and quality level at which they can be processed. If an error message appears “Not enough memory” during one of the processing steps, either reduce the accuracy level (for the Align Photos step) and the quality level together with the number of faces (for the Build Geometry step), or reduce the number of photos in your project. Tables listing the RAM memory requirement with reference to the number of photos and the processing quality can be found at the bottom of the Tips & Tricks page on the wiki of the Agisoft website (make sure to look at the Height Field table of the Build Geometry step, not the Arbitrary table)

1. Also, a

suboptimally framed bounding box could cause a memory issue.

1.4.2 Align photos

• Some camera positions were not reconstructed: this can happen when no feature points were found on some images or not enough quality texture information was available to reconstruct

1 http://www.agisoft.ru/wiki/PhotoScan/Tips_and_Tricks

− 19 −

the camera position. Cameras that failed to align are represented as blue dots in the Model view, as opposed to blue rectangles representing the sensor orientations and normals of aligned cameras. Also the Workspace pane shows the number of reconstructed camera positions next to the number of photos for each chunk. When the number of non-reconstructed cameras is limited, this can be ignored. If a high number of cameras could not be reconstructed, a potential solution would be to increase the number of points per photo used for alignment in the Tools -> Preferences menu and redo the alignment. However, check if there are no obvious reasons for a failed alignment: blurred or too dark images,…

• A misalignment of some camera positions occurred: camera positions were reconstructed but they are pointing in the wrong direction or clumped together at erroneous positions. Either rerun the alignment on a higher accuracy setting, or select the corresponding images name in the Workspace list or Photos pane, right-click and choose Disable or Reset alignment. Either way, these photos and their resulting outlier points will not be taken into account for further processing.

1.4.3 Optimize

• A general model warping “bowl” effect is still present after optimization in a project without ground control points: reduce the setting for camera accuracy further by a factor of 10 and click OK to rerun the optimization.

• The point cloud doesn’t make sense anymore after running optimization: increase the setting for camera accuracy (in case of a project without ground control points) or marker accuracy (in case of a project with ground control points) by a factor of 10 and click OK to rerun the optimization.

• The point cloud is still broken after following the troubleshooting above: restore the alignment (close without saving and open the last saved project) and check the errors on the camera positions. Disable the camera positions with the largest (or all unacceptable) errors by selecting -> right click -> disable. Run Optimize… again.

• Error estimates are still not acceptable after running optimize. Check which camera positions (for projects without ground control points) or marker positions (for ground control points) have the largest error. Disable these by unchecking the corresponding box and click Update. Optionally, rerun Optimize…

1.4.4 Build geometry

• PhotoScan crashes during Build Geometry, showing an Agisoft crash reporting window: if this issue occurs with GPUs enabled, check if the latest drivers are installed and if the crash also occurs with GPUs disabled. If it does, contact support and send the log file.

• PhotoScan crashes at the end of the Build Geometry step, displaying an error message relating to the graphics card, or PhotoScan doesn’t crash but shows and empty Model pane: this is typically the case where the actual build geometry calculations have finished successfully, but the graphics card is not able to visualize the high number of triangular faces (depending on your graphics card, this may occur when the number of faces exceeds 20,000,000 or more). This can be prevented by either setting a limited face count in the Build Geometry dialogue box instead of allowing the software to calculate the maximum achievable number of faces, or by preventing PhotoScan from visualizing the model after finishing the build geometry. The latter can be done by creating a new, empty chunk before starting the build geometry by right clicking in the Workspace pane and choosing Add Chunk. Double

− 20 −

clicking the new (empty) chunk name will make it the active chunk (it will be displayed in bold font). You can then right click the chunk containing the data to be processed and choose Build Geometry from the context menu, or use the Batch Process module from the Workflow menu; make sure you check the correct chunk to be processed in the latter case. This method will keep PhotoScan in the active (empty) chunk while processing the data chunk in the background, without attempting to visualize the data chunk. You can safely close PhotoScan after processing; upon restarting PhotoScan, the empty chunk will still be the active one. Another method to prevent PhotoScan from visualizing an excessively large geometry is to run Build Geometry in point cloud geometry type first (which takes only minutes), switch back to Point Cloud view mode on the toolbar and rerun Build Geometry at the desired settings. The model view will stay in Point Cloud mode even after build geometry is finished and you can export the end products from the File menu.

• The geometry contains noise (spikes where there should be no spikes,…): rerun the build geometry on a higher quality setting or edit the geometry: choose one of the Selection Tools from the toolbar and select the erroneous geometry from in the 3D view (make sure not to select collateral geometry due to the perspective). The selected faces will be highlighted. Press Delete and go the menu Tools -> Close Holes… to fill up the deleted geometry with flat faces. Set the appropriate hole threshold level and click OK. Alternatively, you can export your mesh obtained after Build Geometry by choosing Export Model… from the File menu to third party software for advanced editing. Afterwards, save the mesh in a PhotoScan compatible format (.obj or .ply) and import it back to PhotoScan by choosing Import Mesh… from the Tools menu. Check if there is no physical reason for the noise (camera focus blur,…).

1.4.5 Export products

Exporting to Orthophoto or DEM geotiff fails for a very large project of multiple merged flights: depending on your system, the memory may not be sufficient to write the geotiff. In the Export Orthophoto or Export DEM dialogue box, you have the option to split the project in different geotiff blocks with limited dimensions. Check the Split in blocks radio button and fill out the maximum dimensions, such as 10000 by 10000 pixels. The export region can also be adjusted (in the case of limited memory, decreased) to a specified coordinate extent by clicking Estimate in the Region part below in the Export Orthophoto/DEM dialogue box, checking the Setup boundaries option and filling out the minimum and maximum coordinates.