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Extract fromNCTech Application Notes & Case StudiesDownload the complete booklet fromnctechimaging.com/technotes

[Application note – Queensferry Road, Edinburgh]iSTAR & Agisoft PhotoScanDate: 12 November 2015Author: Araceli Perez Ramos, Application AssistantOrganisations involved: NCTech, Agisoft PhotoScanProducts used: NCTech Immersive Studio, iSTAR and Agisoft PhotoScanPoint clouds using NCTech iSTAR 360 HDR imagesThe iSTAR 360 degree camera provides rapid,automatic HDR (High Dynamic Range) 360 imaging and can be used as a standalonedevice to create point clouds, especiallyindoors or in challenging lighting conditions.iSTAR can be used to provide HDR imageryrapidly with up to nine exposures and a totalEV range of 27 f-stops. The aim of this report isto test the Agisoft PhotoScan software, usingiSTAR images to create 3D point clouds and/or adigital surface model (DSM). The results of theproject showed that iSTAR provides the ability toefficiently capture HDR colour images for pointcloud creation, even in low light conditions.NCTech Ltd 1 Boroughloch Square, Edinburgh, EH8 9NJ, UKT: 44 131 202 6258 - www.nctechimaging.com3

The aim if this report is to show the required workflow to achieve ahigh quality coloured point cloud using NCTech iSTAR imaging andAgisoft PhotoScan.01. Software installation02. Photo Capture03. General Workflow04. Results05. Conclusion06. Acknowledgements“Capture with current analysis” iSTAR mode: This is a default iSTARsetting which activates automatically after taking the first photo.When the iSTAR camera takes an image, it first analyses the wholescene to establish the appropriate exposure value averaged acrossthe 360 degree view. These settings are then saved by default,meaning analysis time can be saved between multiple captureswithin similar conditions. However, for scenes with very changeablelight conditions between shots the function should be cancelled bypressing the green arrow on the top left corner, the new scene isthen analysed during the next capture.01. Software installationInstalling NCTech Immersive dio/Installing Agisoft er/02. Photo CaptureBefore loading photos in PhotoScan it is required to select those mostsuitable for model reconstruction. Considering general environmentalrequirements for Agisoft PhotoScan performance: Avoid un-textured, shiny, mirror or transparent objects. Avoid unwanted foregrounds. Avoid moving objects within the scene to be reconstructed.02.01. PLANNING STATIONS.Planning capture strategy in advanced is critical. You should considerthe following recommendations: Ensure the number of photos gives enough coverage to avoidblind zones. To reconstruct an area, it is necessary for it to bevisible in at least two images. Image overlapping should be 60% or more. The object to be reconstructed should take up the maximumarea in the photo.02.02. CAMERA SETTINGS.ISO value: in general, the ISO level should be set to the lowest value.The lower the ISO value, the lower the noise. Nevertheless, dependingon the light conditions, a lower ISO value may increase the exposuretime greater than desired, in which case a higher ISO value can beused.HDR value: iSTAR can be set as “Single exposure”, “HDR ON” (5exposure levels), or “HDR PRO” (9 exposure levels). In general, “HDRON” gives excellent results for indoor capture. However, where thelighting conditions are very extreme with very high levels of light anddark shadows to be captured in the same scene, HDR PRO will providebetter results for building point clouds.Img. 02.02. “Capture with current analysis” mode activated.03. General workflowGeneral iSTAR workflow within Agisoft PhotoScan differs slightly fromstandard, which commonly uses frame images instead of panoramasbut it is nevertheless still user-friendly. The aim of this section isto explain the general workflow using iSTAR data within AgisoftPhotoScan workflow.03.01. PROCESSING PANORAMAS INTO NCTECH IMMERSIVE STUDIO.Firstly, it is necessary to process iSTAR raw data using NCTechImmersive Studio in order to produce stitched equirectangularimages. The Immersive Studio stitching process uses the specificiSTAR calibration file which is created in controlled conditions duringNCTech the factory calibration process for each camera. Processingimages in NCTech Immersive Studio therefore means the userbenefits from this precision calibration with reduced stitching error.AutoPano Giga 4.2 produced by Kolor, can also be used for stitching ofiSTAR images as it works with iSTAR raw data.NCTech Immersive Studio automatically sets the output imageresolution to maximum (10K), or alternatively resolution can beselected from several other pre-set options (2K, 4K or 16 Mpixel).Resulting point cloud resolution and therefore accuracy, relatesdirectly to the input image resolution, therefore maximum resolutionis recommended.NCTech Immersive Studio has a simple and user-friendly interface. Toprocess iSTAR raw data in Immersive Studio just drag and drop thecorresponding image folders on to the Immersive Studio window,or select the corresponding directory. Both options lead to the sameresult. By default, the output directory is set the same as the inputdirectory, but can be changed easily by clicking on the dotted button.Img. 02.01. Low light condition in which iSTAR can provide high qualityresults working with HDR ON values.For further information about how to use Immersive Studio o/NCTech Ltd 1 Boroughloch Square, Edinburgh, EH8 9NJ, UKT: 44 131 202 6258 - www.nctechimaging.com4

Img. 03.01. NCTech Immersive Studio interface.After processing iSTAR raw data in NCTech Immersive Studio,panoramas will appear into an “Output folder” in *.jpg format.Img. 03.04. Camera Alignment in Agisoft PhotoScan.03.03. BUILDING DENSE POINT CLOUD, MESH AND TEXTURINGBuilding the dense point cloud, mesh and texture doesn’t require anychange from standard workflow using frame images instead of iSTARspherical images, so a detailed explanation of these functions are notincluded in this Application Note. The General workflow correspondingto the specifically required process is however considered to showthat it does not change from the frame images common workflow.Based on estimated camera positions and pictures, a dense pointcloud is obtained after camera alignment stage (Workflow BuildDense Point Cloud).Img. 03.02. Panorama in *.jpg format, after processing in ImmersiveStudio.03.02. LOADING PHOTOS, SENSOR TYPE AND CALIBRATION.After processing iSTAR raw data, *jpg panoramas must be importedinto Agisoft PhotoScan (1. Add Chunk 2. Workflow Add Photos orcorresponding icon) then select the appropriate sensor type for iSTAR.(Tools Camera Calibration, Camera types: Spherical).Img. 03.05. Dense point cloud in Agisoft PhotoScan.PhotoScan reconstructs the 3D polygonal mesh based on the densepoint cloud (Workflow Build Mesh).Img. 03.03. Camera Calibration window in Agisoft PhotoScan.Img. 03.06. Mesh in Agisoft PhotoScan.Note that calibration parameters are disabled. Because calibrationparameter characteristics for each iSTAR camera have alreadybeen applied during the Immersive Studio stitching process (See03.01. Processing panoramas into NCTech Immersive Studio) nofurther calibration data needs to be applied in the Agisoft PhotoScanworkflow.After geometry is reconstructed, the model can be textured(Workflow Build Texture).03.02. CAMERA ALIGNMENT.Agisoft PhotoScan searches for common points on input photos andautomatically matches them. At this stage PhotoScan calculates thepositions of each photo station/placement and its external orientation(Workflow Align Photos) from which a sparse point cloud and camerapositions are obtained.Img. 03.07. Textured Mesh in Agisoft PhotoScan.NCTech Ltd 1 Boroughloch Square, Edinburgh, EH8 9NJ, UKT: 44 131 202 6258 - www.nctechimaging.com5

Img. 03.08. Textured mesh. 702,577 faces.From these 11 panoramas a point cloud of 5,496,728 points and amesh of 702,577 faces was obtained, following the general AgisoftPhotoScan workflow as described above.04. ResultsColoured point clouds, meshes or intermediate outputs of the processcan be obtained using the described workflow in Agisoft PhotoScan.The aim of this section is to show the results that can be achievedusing the NCTech iSTAR camera within Agisoft PhotoScan.The project selected for the purpose of this standard workflowexplanation required 11 panoramas, 5 of them under the archway and6 external to it.05. ConclusionHigh quality coloured point clouds can be obtained from usingiSTAR within Agisoft PhotoScan, following the general workflowas described here. The benefits of working with NCTech solutionscombined with the Agisoft PhotoScan for high quality coloured pointclouds and meshes are:Only one iSTAR shot is needed to cover a 360 environment surface,which means saving time against taking a larger amount of images tocover the same area with a non 360 camera.Larger surface covered per lens. The iSTAR fisheye lens not onlycovers a 360 view, but also a larger area per lens.Img. 04.01. Camera positions used in the current project in AgisoftPhotoScan.A knowledge of photography techniques is not needed since iSTARanalyses the whole scene and automatically calculates the mostsuitable camera settings for the full 360 view.Simple to use, minimal training needed. iSTAR and NCTech softwareare designed to be highly automated and user friendly, minimaltraining is required.High performance output in difficult lighting conditions. iSTAR canprovide high visual quality images in a wide range of lightningenvironments thanks to automatic HDR settings and EV range of 27f-stops.Texture Quality. iSTAR’s whole scene analysis in combination with itsHDR imaging enables the creation of high resolution models with highquality surface textures.Img. 04.02. Coloured point cloud. 496.728 points.To conclude, iSTAR provides imaging which is highly suitable forphotogrammetry purposes within Agisoft PhotoScan. It providesparticularly strong benefits in low light or high contrast environments,indoors and where there are complex architectures.06. AcknowledgementsNCTech greatly thanks the Agisoft PhotoScan Teamhttp://www.agisoft.com/, specially Alexey Pasumansky for theircollaboration and technical support in this Application Note.Img. 04.03. Textured Mesh (detail). Notice the quality of textureprovided by NCTech iSTAR within Agisoft PhotoScan.For further information about iSTAR or NCTech software visitwww.nctechimaging.com or contact us [email protected] Ltd 1 Boroughloch Square, Edinburgh, EH8 9NJ, UKT: 44 131 202 6258 - www.nctechimaging.com6