ANSWERS TO YOUR
TECHNICAL QUESTIONS.
How do I crop my mosaic?
You can crop your mosaic while exporting it by selecting the "Crop area" function. The area is specified as a Shapefile. Such a Shapefile can be easily generated using the DEM Editing module by creating a selection and saving it to disk.
How do I prevent the software from modifying radiometry / pixel value (e.g. thermal imagery) during the mosaic creation process?
You should disable the color balancing option in the Mosaic Creation dialog.
How can I export seamlines?
The seamlines can be exported in an ESRI Shape file by using the "Export seamline" button in the Mosaic Editing module.
Why do I get a "Cannot connect to server" message when launching Correlator3D?
This error is due to the absence of a proper internet connection, or to a firewall blocking your connection to our servers. Make sure that no firewall is blocking "Correlator3D.exe". You can either deactivate temporarily the firewall or add an exception to it. Note that this exception must be for the address “updatec3d.simactive.com” through TCP port 6662.
How do I transfer my license to another PC?
The following procedure must be followed to transfer a Correlator3D™ license to another PC. To avoid losing the license, it should be transferred before formatting the PC or reinstalling Windows.
The “Remote Update System” application is required for the following steps. This application can be searched from the Windows Start menu (under SimActive) or found in the Correlator3D installation folder at this location, by default: C:\Program Files\SimActive\Correlator3D\Tools\C3D_RUS.exe
1. ON THE DESTINATION (NEW) COMPUTER
a) Install Correlator3D.
b) Start the "Remote Update System" application
c) Choose the “Transfer license” tab.
d) Click on the “…” button
e) Save the file in an easily traceable location.
f) Click on “Collect and save information”.
g) Copy the file on the computer which already has the Correlator3d license (source computer).
2. ON THE SOURCE (OLD) COMPUTER
a) Start the "Remote Update System" application
b) Choose the “Transfer license” tab.
c) In the middle of the screen, select the key to be transferred (there should only be one).
d) Click on the “…” button corresponding to “Read the recipient information file from" and choose the file generated during step 1.
e) Click on the “…” button corresponding to "Generate the license transfer file to" and choose an easily retraceable location. Note that if this file is lost, then the license will be lost.
f) Click on “Generate license transfer file”.
g) Copy the file on the destination (new) computer.
3. ON THE DESTINATION (NEW) COMPUTER
a) In the Remote Update System, select the “Apply license file” tab.
b) Click on the “…” button
c) Select the file created during step 2.
d) Click on the “Apply update” button
Why the automatically generated DTM does not meet my accuracy requirements?
If your final deliverable is a high accuracy DTM, you should use a combination of automatic and manual editing of the DTM. However, the automatically produced DTM is in general precise enough for generating accurate orthophotos.
Why some features have been incorrectly removed while extracting the DTM?
There are situations for which it can be difficult for the software to correctly identify features vs. ground. In such cases, consider doing the following:
1) When extracting the DTM, use an exclusion zone defined through a Shapefile (vector) file for the region you want to leave intact. This will prevent the software from modifying that region. An easy way to define an exclusion zone is by using the DEM Editing functionality. Simply perform a selection around the region, and save this selection using the corresponding button in the side toolbar. This selection can then be used as an exclusion area during DTM extraction. If several areas are required, simply save the new selection under the same filename. This will result in appending the file.
2) Some isolated erroneous elevation points in the DSM may lead to sub-optimal results during DTM extraction. In that case, simple edit the DSM before performing the extraction.
Is it possible to crop a DEM to keep a smaller area only?
Yes, you can select your region by selecting an area and use the Crop function.
Why my aerial triangulation results are not meeting my expectations?
Several reasons can cause this. For more information, please refer to the document "How to optimize accuracy" from the Learning section of our website.
When should I use the exhaustive tie point extraction instead of standard?
You should use the exhaustive tie point extraction mode for difficult areas such as dense forest / large waterbodies, or when there was not enough tie points generated from the standard mode.
What is the difference between boresight and sensor calibration?
In the boresight calibration process, the software computes the error component that is common to all exterior orientation estimates. This usually corresponds to the relative position/orientation of the camera to the GPS/IMU unit.
The sensor calibration consists in adjusting the camera parameters based on the camera type used. These values may include focal length, principal point, radial and decentering distortion parameters or LUT values.
How can I convert a GCP into a check point?
Edit the GCP you want to modify using the corresponding button in the project tree or by right-clicking on it in the main window. Expand the Information section. From the Type drop-down menu, select "Check point". Click on "Save and Close" button.
How do I apply a GEOID offset?
A GEOID offset can be applied in the Exterior Orientation Parameters menu within the Project Creation Wizard. Simply add the GEOID offset value in the Altitude Offset field.
Why am I getting a message telling me that LLX, LLY or LLZ parameters are missing from my satellite project?
With a text editor, open the .TIL file corresponding to the RPB or RPC files you are creating the project with. At the end of the file, right after the last parameter, inside the GROUP element, insert the following 3 lines:
LLX = 0;
LLY = 0;
LLZ = 0;
While using a digital polynomial distortion model, do I need to specify all parameters?
You only need to enter the focal lenght and pixel size of the camera. The other parameters can be left at 0, and will be automatically calculated during aerial triangulation.
Where can I find the pixel size of my camera?
Correlator3D should automatically detect your camera and retrieve its pixel size from its database. However, if you need to manually set this value, you can find the pixel size of a camera on the camera manufacturer website or reference websites like "Digital Camera Database" (https://www.digicamdb.com/). Note that the pixel size is sometimes referred as "pixel pitch".
The pixel size can also be derived from the the size of the sensor (or CCD size) by the number of pixels for the height and width, respectively.
Example:
Sensor size = 23.7 x 15.7 mm
Image size = 4928 x 3264 pixels
Pixel size = 23.7 / 4928 * 1000 = 4.81 µm (or 15.7 / 3264 * 1000 = 4.81 µm)
An average can be done in between the height and width value if they differ.
Note that the pixel size is expressed in micrometers in Correlator3D.
When should I define several cameras when creating a project in Correlator3D?
If you are using a multi-camera system, then you should create your project with a single group of multiple cameras. If your project involved several missions, drones or was acquired during several days, then the project should be defined as several groups of one camera.
What is the optimal overlap and sidelap required by Correlator3D?
The optimal values for overlap (between successive images) and sidelap (between adjacent flightlines) are governed by photogrammetry principles, not Correlator3D.
For medium/large format cameras mounted on aircrafts, the overlap should be at least 60% of the image size. The recommended sidelap is 30%.
For small cameras mounted on drones, the recommended values for overlap/sidelap are 70%/50%.
How does Correlator3D handle meridian convergence?
The Omega/Phi/Kappa (OPK) orientation system is defined in a projected system while the Roll/Pitch/Yaw (RPY) system is defined in a geographical system. In Correlator3D, processing occurs in a projected system. This means that if RPY is provided as input data, a conversion to OPK is first perfomed. This conversion does take into account the meridian convergence through a minimization based on geographical coordinates. Consequently, the conversion results may slightly differ from one project to another.
How do I add GCPs and checkpoints to my project?
GCPs and checkpoints can be added using the GCP Editing tool, which is part of the aerial triangulation module.
How can I use a distortion table with steps larger than the 1 millimeter required by Correlator3D?
You can use a simple spreadsheet program (e.g. Microsoft Excel) to interpolate intermediate missing values.
How can I see footprints of my images after creating my project?
In order to display footprints, a DEM must be loaded. If no DSM or DTM was created yet, you can generate a flat DEM using the "Create Seed DEM" from the "Processes" menu. A coarse DEM can also be created if aerial triangulation was already performed, using the corresponding button in the toolbar.
Does Correlator3D produce ellipsoidal or orthometric height?
Correlator3D uses the input elevation reference from the geotags or the input exterior orientation parameters. If GCPs are used, it will match their elevation reference. The output height thus depends on the input used.
Why are my computer resources not completely used during processing?
In general, a saturated hardware component (e.g. CPU or GPU) is a sign of a unoptimized or badly designed software. Correlator3D balances the use of computer resources to avoid bottlenecks and as such, monitoring your PC will not provide a good metric of its performance. In many cases, the limiting factor will not be the CPU/GPU, but reading the data from disk. You should consider using an SSD, at least to store your input images and the temporary folder of Correlator3D (you can specify this folder in the General Settings dialog from the File menu). Also note that the resource usage varies depending on the Correlator3D module used.
Why am I getting a warning message that no OpenCL-enabled CPU was found?
If you have an Intel CPU, you need to install the OpenCL driver. While this driver is not required for processing, it can lead to improved performance while using the software. You can download the driver from the following link (Section: "OpenCL™ Runtime for Intel® Core™ and Intel® Xeon® Processors"):
How can I reduce processing time?
- Make sure that your computer has recommended specifications (CPU, GPU, SSD, etc.)
- When creating a project, make sure your overlap/sidelap are not too high. If so, you should consider removing some images (e.g. one every two).
- When generating the DSM, do not select a resolution that is too high unless it is absolutely required. Also, reducing the vertical accuracy will accelerate the processing.
When should I use the crop option?
When artefacts are systematically present in the periphery of each input image, for example drone parts occluding the photos.
How do I generate true orthos?
You must have a DSM loaded (with buildings and other structures) and select the "DSM-based option" in the orthorectification dialog.
How do I generate a new set of orthophotos for the same project without overwriting the original files?
You can create another folder for new orthophotos by using the function "Add folder" in the "Orthos" section of the project tree. It is always possible to switch back to the original folder by using the same functionality.
How can I generate orthophotos for only a subset of images from my project?
You can disable individual images, and even entire flightlines, from the project tree. The disabled images will not be used during orthorectification.
Can I use an external DEM (e.g. LiDAR) for orthorectification?
Yes, you first need to add the DEM in the project tree. The currently loaded DEM will be the one used for the orthorectification process.
How do I modify seamlines?
After entering the mosaic editing module, you need to select the block containing the seamlines that you want to modify. Then, simply click on the "Start Seamline Editing" button. You can select a specific seamline by a click, which will trigger the editing functions. Once the seamline is modified, click "Save" and select "Apply" for the mosaic to be updated. To save processing time, you can modify multiple seamlines before updating the mosaic.
How can I improve the global colors of my mosaic?
You can adjust the global colors of the mosaic using the "Color Adjustment" tool to enhance its visual appearance. This tool allows modifying the levels of the mosaic, i.e. making adjustments to the brightness, contrast, and gamma for each individual channel or for all channels together.
How can I change the feathering size for a specific seamline?
When moving points of a seamline, the red region displayed around it corresponds to the feathering zone i.e. the region where a progressive transition is made between an image and another. You can modify the size of each seamline (feathering) while editing a mosaic.
Can I remove one orthophoto from my mosaic?
Once a mosaic has been generated, it is impossible to remove one orthophoto. However, it is possible to minimize the contribution of a specific orthophoto by modifying a seamline accordingly.
What could be the reasons behind color balancing issues?
Mirror surfaces (e.g. waterbodies) may affect color balancing because of their widely varying appearance from one viewpoint to another. You should remove these by using an exclusion zone.
How can I validate results against GCPs or check points?
Once the mosaic creation is completed, the mosaic will be displayed with superimposed GCPs / checkpoints. This allows to visually assess the accuracy of the mosaic.
How can I generate a mosaic from only a subset of my orthophotos?
You can disable specific orthophotos from the project tree before starting the mosaic creation process. The mosaic will be created using the enabled orthophotos only.
How can I export my mosaic?
You can use the export tool of the Mosaic Editing module, which has different options (tiling, format, etc.)
Why do I get the error message "Current license does not allow running this version of Correlator3D"?
This means that you have installed a newer version of Correlator3D while your license is no longer under maintenance. For a license upgrade, please contact us.
Why am I getting the message "Unable to access sentinel run-time environment (H0033)"?
This message means that there is a communication error between Correlator3D and the license manager installed locally (called "Sentinel Runtime Environment"). Reasons may include the license runtime environment (RTE) not installed properly, a personal firewall software blocking communication with the run-time environment (RTE), or another software using the same port that the RTE uses (port 1947).
To fix the error, you should try the following:
1. Open a web browser and connect to http://localhost:1947 which will give the status of the RTE. If it is not possible to connect to this page, start "Reset License Environment" from the Windows Start menu, under SimActive, and start the software again.
2. Check your personal firewall software. There are many types of personal firewall software including Norton Internet Security (the Firewall is one component of this software), Zonealarm and others. By default, most personal firewall software will request permission to allow access for the RTE the first time it is run. If access is allowed, there will be no problem. However, if access is denied, then you will encounter communication problems. To resolve such problems, either disable the Firewall completely (note: this option has risks, contact your firewall vendor for details) or create a rule/exception in the firewall to allow the RTE (if there is an option to create a rule/exception based on a port number, allow port 1947)
3. Check that there is no other application that uses the RTE registered port (Port 1947). If you find such a program, disable it and run the HASP application again. To check which service uses port 1947, do the following:
- Open a command prompt.
- Type: CDocuments and Settingsuame>netstat -a -b
- Right-Click --> Find --> 1947
- Check if 'hasplms.exe' is the only application using port 1947.
4. In Brazil, a software commonly used for online banking (Warsaw from GAS Technologia) might be causing this issue as it prevents most software tools from using internal ports. Uninstalling this software solves the problem.
Why am I getting the error message "This module requires an OpenCL-enabled device to run"?
This situation happens if the graphics card is not supported or the corresponding drivers are not installed.
Where can I find a quickstart guide for Correlator3D?
You can find a quickstart guide in the Help menu of the software or in the "Learning" section of our website.
This guide is designed for first-time users and covers a standard workflow from input imagery to final products. A more detailed description of the software can be found in the user’s manual.
How do I update my floating license?
If you need to update your floating license (e.g. for maintenance renewal), you need to access the PC where the dongle is plugged in, and execute the program "Update Network Keys" located in the installation folder ("C:\Program Files\SimActive\Correlator3D\"). The computer should have access to the internet.
How do I force Correlator3D to run on one of my multiple graphics cards?
If you are using an NVIDIA graphics card, you need to make sure Correlator3D will run on the correct one by following these steps:
1) Right click on desktop and select "NVidia Control Panel"
2) Click on the "Manage 3D settings" tab from the left menu
3) Select the "Program Settings" tab
4) Click Add, then browse to C3DGui.exe located in the Correlator3D installation folder (e.g. "C:\Program Files\SimActive\Correlator3D")
5) Set the preferred graphics processor to "High-performance NVIDIA processor".
If you are using an AMD graphics card, you can follow these steps:
1) Right-click the Desktop and select AMD Radeon Settings from the menu.
2) Select Preferences.
3) Select Radeon Additional Settings.
4) Navigate to Power > Switchable Graphics Application Settings and the click Add Application.
5) Select Correlator3D (C3DGui.exe) and click Open.
6) Under Graphic Settings choose High Performance and click apply.
Why does my DTM still contain buildings and/or forested areas?
There are cases where it is difficult for the software to distinguish the ground from features. This could be due by a DSM resolution that is too low, or by the ground simply not visible enough (e.g. dense forest).
When some features were not properly removed, consider doing the following:
1) Generate the DSM at a finer resolution. The more points, the more chances the terrain is going to be detected.
2) Use a vector constraint when extracting the DTM. This constraint can contain points belonging to the ground, helping the software.
3) Use the DEM Editing tool to fix the issues. You can simply select the features to be removed, and use the "Delete and Fill" function.
Why did Correlator3D smooth out some natural terrain features?
In such cases, it can be challenging for the software to identify objects versus terrain features. You should use an exclusion zone to avoid filtering in such areas.
How can I keep linear 3D features such as bridges from being removed?
You can use an exclusion zone to prevent such features to be filtered. Also, you can copy/paste the feature from the DSM to the DTM using the DEM Editing module.
Can I run the DTM Extraction process on a subregion of the DSM only?
Yes, you can select a polygonal region and use the DTM Extraction function in the DEM Editing module.
Why do I obtain a DSM that presents noisy areas?
Your input data quality might not be sufficient to support the generation of higher resolution DSMs. You should use the optimal resolution suggested by Correlator3D to see if it improves results.
Why did Correlator3D produce a red-looking DSM?
Such a situation occurs when there are too many extreme elevation values (high or low), affecting the overall shading of the DSM. You should try to remove such large values using the DEM Editing module.
Why Correlator3D generates my DSM with holes?
There are many reasons that could lead to holes. These are the most frequent:
- The overlap between images is less than 50%. This means that some parts of the project cannot be seen in more than one image, making DSM generation impossible.
- The DSM resolution is too high considering the quality of the images. If the images are blurry, it becomes hard for the software to match the features from all images at maximum resolution. You should consider reducing the resolution of the DSM.
- Aerial triangulation is not adequate. If the positions and orientations of the images are not precise enough, it can make the matching process difficult, leading in holes.
It is also possible to fix some of the issues using the DEM Editing module. As a an example, you could capture a selection around a hole and then perform a "Delete and Fill".
Why am I getting the message "Correlator3D is unable to generate a DSM using the supplied input data"?
These are the possible causes:
- Insufficient overlap between images is a common cause. Generating a coarse DEM using the Aerial Triangulation module and verifying the footprints can help identify an issue.
- The resolution you specify for the DSM might be either too high or too low. While Correlator3D supports a wide range of resolutions, some projects might have some particularities that do not allow a certain resolution.
- The aerial triangulation that was performed on the project is problematic. You should consider validating your AT results again and make sure that all disks are green and that calibrated camera parameters are not out of expected bound.
The same recommendations apply when the message "There is no overlap between the images. Skipping, continuing with next entry" appears for some images in the log window.
What bit depth does Correlator3D support for elevation when importing a GeoTIFF DEM?
32-bit floating point elevation values are supported.
How do I generate a point cloud?
The production of a point cloud occurs in parallel with DSM generation. You should select the option "Generate Point Cloud" from the DSM Generation dialog box.
Can I resume DSM generation if processing was interrupted?
The DSM tiles (corresponding to each pair of successive images) that were already generated can be found in a temporary DSM folder used by Correlator3D. The path of this folder can be found in the General Settings dialog from the File menu.
Using the "DEM Merging" tool (from the "Processes" menu), you will be able to merge the files contained in this folder and retrieve the portion of data that was processed.
Merge the temporary files and save the corresponding DSM. Disable images that were already processed from the project tree. Generate a second DSM, and merge it with the first DSM using the Merge tool.
Note that once you start a new DSM Generation, all the DSM tiles located in the temporary folder will be deleted.
How do I remove objects or undesired artifacts from a DEM?
You should use the "Delete and Fill" function. The interior of the selected polygon will be interpolated from the surrounding elevation values.
How do I bring back a 3D feature that has been removed during DTM extraction (e.g. bridge)?
You can use the "Paste DEM" tool to bring back a portion of the original DSM.
Why should I perform more than one bundle adjustment step?
There are three common situations for which more than one iteration may be required:
1. You want to run a first iteration of bundle adjustment without GCPs, and then run a second bundle adjustment with GCPs (e.g. troubleshooting, large projects, GCPs available at a later stage).
2. In cases for which you want to highly constrain bundle adjustment parameters, this may require running 2-3 bundle adjustments to reach the optimal solution.
3. If a first bundle adjustment is necessary to account for large adjustments on the EO parameters (such as large offsets in the image positions, important adjustments on the attitude angle, 90 or 180 kappa rotations), it can be a good idea to follow with a second adjustment to fine tune the solution after the large adjustments of the first pass.
Why does the software stop running while extracting tie points?
This is usually related to the use of an improper graphics card, or an old driver. You should check that your graphics has a supported GPU and that your driver is up-to-date.
Why are my image positions being modified too much during bundle adjustment?
The bundle adjustment process will perform a minimization of image residuals. Hence, it could lead to modifications on the image positions that are larger than expected, but still leading to good residuals. You should use the "Constrained" mode to set maximum modifications permitted during bundle.
Why after completion of the tie point extraction process, all my image disks are displayed in red?
This is a normal behavior, as no bundle adjustment has been performed yet. It shows that the initial residual errors of the camera calibration and exterior orientation, before aerial triangulation, are large. Once bundle adjustment is completed, the residual values should improve.
What are the steps for performing aerial triangulation?
Aerial triangulation should be performed in the following order:
1. Tie Point Extraction
2. GCP Creation (if required)
3. Tie Point Editing (if required)
4. Bundle Adjustment
5. Quality Assessment
6. Image List Filtering (if required)
How do I manually add tie points between two images?
To manually add a tie point, you must first create a link between two adjacent images. If the link already exists, you can right-click on the yellow line linking the two images to access the Tie Point Editing window. Using your mouse, you can click in one image and drag to same location to add the point on the other image. Zoom in to refine the position of the point and accept its final location by saving. Tie points, when manually measured, must be identified on each image with the best possible accuracy (at the pixel level).
Note that if there are already existing tie points (visually identifiable as stars), then it is recommended to use these to create new links.
How can I merge LAS files?
If the LAS files have been generated in Correlator3D (i.e. with their corresponding DSM files), then the DEM Merging tool will allow that function. You simply need to select the .smf files and the corresponding .las files will be automatically merged as well.
Why am I getting an invalid signature error when installing the software?
Correlator3D is signed with a digital certificate from the third-party certificate authority SSL. Computers that do not have a live internet connection might not be able to download the updated certificate authority list and this can cause the invalid digital signature error.
To resolve this:
1) Download the latest SSL Security Certificates here.
2) Unzip the four certificate files (.crt).
3) Right-click on the first certificate file and select Install Certificate.
4) Follow the steps of the Certificate Import Wizard.
5) Repeat steps 3 and 4 for the three other certificates.
6) Install Correlator3D.
How do I remove noise in areas such as waterbodies?
You can use the function "Set Elevation" to force an entire surface to be completely flat.