PrecisionMapper Local is an offline desktop tool which creates an Orthomosaic of your survey. It provides a step-by-step approach which is used to create the various essential layers for the formation of an Orthomosaic. These layers are as follows.
1. Camera Layer
2. Sfm Layer
3. Dense Point Cloud Layer
4. Grid Point Cloud Layer
5. Mesh Layer
6. Ortho Layer
To create an orthomosaic with the help of PrecisionMapper Local in Advanced Mode, follow these steps.
1. Navigate to PrecisionMapper Local. Click Start in Advanced Mode (Figure 1).
PrecisionMapper Local will ask you to start a project in Advanced Mode. Click Ok.
Figure 1: Opening PrecisionMapper Local in Advanced Mode
2. In File menu, click New Project. Provide appropriate details like project name, location and click OK (Figure 2 and Figure 3).
Figure 2: Creating a new project
Figure 3: Selecting a project name and location
3. Click Add Photos and select survey images (Figure 4).
Figure 4: Selecting survey images
4. If your survey is carried out with multispectral sensor, then click Manage Multiband Calibration to calibrate multispectral bands.
Otherwise, click OK to confirm your selected survey images and continue with next steps (Figure 5).
Figure 5: Confirming Survey Images
Note: While adding a survey, the survey images must be provided with their GPS data.GPS data consists of parameters like latitude, longitude, and altitude. Depending upon the type of your drone, your survey images may possess inbuilt GPS data or it might be available in a separate file. If no GPS data is detected, you need to import a separate GPS file (.dat or .csv format file) available in your respective survey folder.
5. In the absence of inbuilt GPS parameters, click Import GPS and select GPS parameters file (telemetry file for PrecisionHawk drones) (Figure 6).
Figure 6: Selecting GPS parameter file (telemetry for PrecisionHawk drones)
6. Adjust the GPS table (Figure 7).
6.1 In Table Formatting section,
i. Select the checkbox if the GPS file possesses a header.
ii. Select column separator as White Space or comma depending upon your GPS file type.
6.2 In Position Input section,
i. Select the column numbers as per respective GPS values.
(For example, as per your telemetry file table, if the Latitude is present in the 4th column, then select 4 in Latitude starting from Column drop-down box. Similarly, select respective column numbers for Longitude and Vertical).
Figure 7: Adjusting GPS values
Generating Camera Layer
Figure 8: Batch Setup Sidebar
Maximum features to use per photos = 40000
Figure 9: Entering recommended values in Batch options dialog box
Note: Following three steps are involved while aligning photos.
Figure 10: Step 1 – Feature Detection in progress
Figure 11: Step 2 – Feature Matching in progress
Figure 12: Step 3 – Sfm in progress
Enter GCP entries (if available) and click Next (Figure 13).
Figure 13: Absence of GCPs
Generating Dense Point Cloud Layer
In Dense Point Cloud Dialog box, select dense point cloud layer resolution level as 2 = Medium Resolution.
Keep the remaining parameters at their default values and click Ok (Figure 14).
Figure 14: Selecting Dense point cloud resolution
Note: Following two steps are involved in the generation of Dense Point layer.
Figure 15: Generating Dense Point Cloud layer - Step 1 (Undistorted Images in progress)
Figure 16: Generating Dense Point Cloud layer - Step 2 (Dense Points in progress)
Generating Grid Point Cloud Layer
In Grid Resample Dialog box, click OK (Keep the Cell size parameter to its default value which is 1 meter)
Figure 17: Default value for generating Grid Point Cloud layer
Generating Mesh Layer
Figure 18: Default values for generating the Mesh layer
Generating Orthomosaic Layer
Output Pixels size/GSD (meters) = Median value
Photo Blend Distance (meters) = 2Down sample = Original Resolution
Figure 19: Selecting values in Orthos dialog box
Note: Following three steps are involved in the generation of an Orthomosaic layer.
(Figure 23 and Figure 24).
Figure 23: Generated Orthomosaic in results folder
Figure 24: Generated Orthomosaic
Generating A DSM (Height map) layer
You can create a Digital Surface Model (DSM) that is a height map using
PrecisionMapper Local- Advanced Mode. In order to create this, make sure that you have
successfully created the Final Mesh layer and follow the steps mentioned below.
1. Select the Final Mesh layer checkbox from the Files pane located at the right side (Figure 25).
Figure 25: Selecting Final Mesh layer checkbox
2. Click Layer. In Mesh, click Export As Height Map (Figure 26).
Figure 26: Selecting Export As Height Map
3. Provide name and save the file. The file will be saved in .TIF format.
4. Select appropriate Ground Resolution value and Click OK (Figure 27).
Note: Select Resolution value as the Median Value (Refer Figure 19 for knowing the Median Value).
Figure 27: Selecting height map resolution
5. Once the DSM file is generated you can quickly view it in 2D View tab located at the
top of the Display pane.
Figure 28: DSM [Darkest spot indicates Deepest region of the survey area]
Note: For any further analysis, you can view this DSM output in other GIS software like,
QGIS, ArcGIS and so on. All you need to do is access the .TIF file with the GIS software.