When the uploaded images contain GPS location data, it is used by Reconstruct to georeference the point cloud reconstruction. Additionally, it is possible to use ground control points. Ground control points (GCP) are landmarks visible on the images for which the geospatial position (latitude, longitude, and altitude) is known. A single GCP can be observed in one or more images.
Users can upload a *.TXT file to the point cloud before processing it (as shown below). This file should contain information about the GCPs, their coordinates, and locations in images. Follow the instructions below to use GCPs in your point clouds.
GCP File Format
GCPs can be specified by adding a text (*.TXT) file to the point cloud as shown in the short video above. The format of the file should be as follows.
The first line should contain the name of the projection used for the geo coordinates.
Check the following section to learn more about supported projections.
The following lines should contain the data for each ground control point observation. One per line and in the format:
<geo_x> <geo_y> <geo_z> <im_x> <im_y> <image_name>
<geo_x> <geo_y> <geo_z>are the geospatial coordinates of the GCP and
<im_x> <im_y>are the pixel coordinates where the GCP is observed. If the altitude of the GCP is not known, set
The geospatial coordinates can be specified in one the following formats.
- WGS84: This is the standard latitude, longitude coordinates used by most GPS devices. In this case,
<geo_x> = longitude,
<geo_y> = latitudeand
<geo_z> = altitude
- UTM: UTM projections can be specified using a string projection string such as
WGS84 UTM 32N, where 32 is the region and N is . In this case,
<geo_x> = E,
<geo_y> = Nand
<geo_z> = altitude
- proj4: Any valid proj4 format string can be used. For example, for UTM 32N we can use
+proj=utm +zone=32 +north +ellps=WGS84 +datum=WGS84 +units=m +no_defs
This file defines 2 GCPs whose coordinates are specified in the WGS84 standard. The first one is observed in both
02.jpg, while the second one is only observed in
WGS84 13.400740745 52.519134104 12.0792090446 2335.0 1416.7 01.jpg 13.400740745 52.519134104 12.0792090446 2639.1 938.0 02.jpg 13.400502446 52.519251158 16.7021233002 766.0 1133.1 01.jpg
For the text file to work, it needs to contain information about at least 3 GCPs (5 Recommended GCPs). Each of these GCPs should be visible in at least 4 images (5 recommended images per GCP). This means that the file should contain at least 12 lines (25 recommended).
Only spaces should be used in the file, tab characters might cause problems with the reconstruction.
Make sure that the images that you uploaded have the same names as the ones you used for creating the GCP file. The system uses image names to match the information in your GCP file.
Once you have created the file, you can follow the instructions in the short video above to upload it to the system and process the point cloud.