Coded Tags can now be used directly in PIX4Dcatch, which are detected and marked automatically by the application. Users only need to load the Point Collection that contains the GCPs, allowing for PIX4Dcatch projects to achieve higher absolute accuracies leveraged by GCPs without the need for tedious manual marking.
IN THIS ARTICLE
Tags are uniquely coded targets that the application can automatically detect in images. Tags are ideal and commonly used for marking GCPs on the field. Tags can be downloaded here.
- The Tags/GCPs should be placed on the ground at a sufficient distance from each other.
- The images should not be blurry and the Tags/GCPs should be clean.
- The Tags/GCP should not be obstructed by any object above them nor by shadows.
- The Tag/GCPs must be large enough in order to be visible in the images.
- Good image overlap makes the automatic Tag Detection results more reliable, with each tag visible in multiple images.
- If unused Tags are visible in the images, automatic Tag Detection can be misleading.
The Tags/GCPs should be evenly distributed in the area of interest. Imagine the area as a large table and the Tags/GCPs as the legs that will support it. If all the "legs" are placed at the same location of the "table", then it will tilt. If the "legs" are homogeneously spread, then the "table" will be stable. Additionally, it is also recommended to place one Tag/GCP in the center of the area to further increase the quality of the reconstruction.
Tags can be automatically detected by PIX4Dcatch. The only requirement is to select the Point Collection before starting the capturing process.
Automatic Tag Detection - Summary
- Display targets on the scene
- Measure the location of the targets
- Turn on the Tag Detection option
- Select your Point Collection
- Start capture
- Process project with GCPs
Automatic Tag Detection - Detailed Description
To select the Point Collection, first visit the Tools at the bottom and select Tag Detection.
Select the Point Collection to use for the automatic tag detection.
Start capturing a project in which the tags are visible. Below the Signal Indicator dialog, the total number of successfully marked tags and the number of point entries in the Point Collection is displayed. If a tag is detected in the image, it will be marked with the corresponding name on white background. If the tag is detected in at least 3 images, the tag label will turn green with a black background. To use a Tag/GCP for processing, it has to be detected in at least 3 images.
During capturing, at least 3 of the marked Tags/GCPs need to be displayed with green labels. Once the project capturing is finished, a capture report will be displayed with the scanned scene and the marked tags.
After capturing, the Point Collection and detected marks can be exported by clicking on Export Points & Marks. These detected marks replace the tedious manual marking and can be used as automatically marked GCPs or as MTPs for further processing in photogrammetry software.
In Pix4Dmatic, the marks can be imported and used as MTPs to improve the 3D reconstruction (1st screenshot below). Alternatively, the GCPs and automatic marks can be imported to improve the positioning accuracy of the 3D reconstruction (2nd screenshot below). To process a project with Tags, please visit Processing projects - PIX4Dcatch.
Importing Marks in Pix4Dmatic
Importing GCPs and Marks in Pix4Dmatic
GCPs and Tags can be marked manually in PIX4Dcatch to have fully automated processing in PIX4Dcloud.
- Open the Project management dialog.
- Select the project.
- Open the Point Collection selection dialog you want to use as GCPs.
- Close the dialog; the GCP icon will turn blue and the selected Point Collection will be displayed. Now, the Mark points is also available.
- Select Mark points.
- Select the GCP from the list to mark.
Mark GCP on an image with a single tap. Hold tapping a bit longer to open the magnifier for more accurate marking. To expand an image or delete a marking, tap the 3 dots at the top right of each image.
- Mark the GCP in at least 2 images.
- GCPs will be shown on the map; marked images will be displayed in green on the map.
- Tap Save.
- Select and mark additional GCPs for the project as before.
To process a project with GCPs, please visit Processing projects - PIX4Dcatch.