add GCP info

Running-Open-Drone-Map.md

@@ -1,11 +0,0 @@
-To run OpenDroneMap on your images move to a directory of images and run the following command:
-
-    ../OpenDroneMap/run.pl
-
-if your images are with capital letters in there extension first run this command to rename the images:
-
-    rename 'y/A-Z/a-z/' *
-
-then the run script
-
-Sit back, grab a coffee and wait

Running-OpenDroneMap.md

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+To run OpenDroneMap on your images move to a directory of images and run the following command:
+
+    ../OpenDroneMap/run.pl
+
+if your images are with capital letters in there extension first run this command to rename the images:
+
+    rename 'y/A-Z/a-z/' *
+
+then the run script
+
+Sit back, grab a coffee and wait
+
+-------
+
+You may also use OpenDroneMap with ground control, in which case you need to create ground control point file.
+
+The gcp_list.txt file is an optional file that allows OpenDroneMap to georeference the textured mesh and create an orthophoto. The input format specifies the x, y, and z of locations in the input images. The format is as follows.
+
+```
+coordinate system description
+x1 y1 z1 pixelx1 pixely1 imagename1
+x2 y2 z2 pixelx2 pixely2 imagename2
+x3 y3 z3 pixelx3 pixely3 imagename3
+```
+e.g. for the Langley dataset:
+```
+WGS84 UTM 10N
+544256.7 5320919.9 5 3044 2622 IMG_0525.jpg
+544157.7 5320899.2 5 4193 1552 IMG_0585.jpg
+544033.4 5320876.0 5 1606 2763 IMG_0690.jpg
+```
+Please note, these locations are not the locations of the camera at the time of the image. If you have this instead, use scripts like these https://github.com/mapillary/mapillary_tools/tree/master/python for inserting that information into your image headers (exif).
+
+Once this file is in place, running is just as easy. Run the script:
+
+    ../OpenDroneMap/run.pl
+
+Sit back, grab a coffee and wait.