Pointi za Udhibiti wa chini

Ground control points ni muhimu kurekebisha mzunguko wa taarifa na kumbukumbu data ili kujua mfumo wa muunganiko.

A Ground Control Point (GCP) is a position measurement made on the ground, typically using a high precision GPS. (Toffanin 2019)

Ground control points can be set existing structures like pavement corners, lines on a parking lot or contrasting color floor tiles, otherwise can be set using targets placed on the ground.

Targets can be purchased or build with an ample variety of materials ranging from bucket lids to floor tiles.

Recommended practices for GCP setting

Keep ground control points visible for all camera locations. Consider the expected ground sampling distance, illumination, vegetation, buildings and all the existing obstacles.

Procure an evenly horizontal distribution of the GCPs within the project, covering high and low elevations. A minimum of 5 GCP works for most of the jobs, and for larger projects 8 – 10 are sufficient. Locate some points near the corners and others in the center, considering that GCP spacing should be larger than the image footprint so that you can’t see more than one GCP in a single image.

In order to ensure each GCP are found in at least 5 images, separate the points 10 to 30 meters from the perimeter of the project. This distance is dependent of the overlapping, so increasing overlapping should reduce the required distance from the perimeter.

GCP file format

Muundo wa GCP file ni mwepesi.

• The first line should contain the name of the projection used for the geo coordinates. This can be specified either as a PROJ string (e.g. +proj=utm +zone=10 +ellps=WGS84 +datum=WGS84 +units=m +no_defs), EPSG code (e.g. EPSG:4326) or as a WGS84 UTM <zone>[N|S] value (eg. WGS84 UTM 16N)

• Mstari wa mbele ni muungano wa X, Y & Z, muungano elementi picha wa jina la file na njia za taarifa za ziada, zilizotenganishwa na kichupo au nafasi:

• Avoid setting elevation values to "NaN" to indicate no value. This can cause processing failures. Instead use 0.0

• Similarly decreasing the no. of digits after the decimal place for geo_x and geo_y can also reduce processing failures.

• safu ya 7 (chaguo) kawaida inachukua lebo ya GCP.

Muundo wa GCP faili:

<projection>
geo_x geo_y geo_z im_x im_y image_name [gcp_name] [extra1] [extra2]
...

Mfano:

+proj=utm +zone=10 +ellps=WGS84 +datum=WGS84 +units=m +no_defs
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

Ikiwa utagawa GCP faili liitwalo gcp_list.txt kisha ODM wenyewe itafuta hilo. Ikiwa lina jina jengine unaweza kuonesha kutumia --gcp <path>. Ikiwa una gcp faili na unataka kufanya georeferensing pamoja na exif file baada yake, unaweza kukadiria --use-exif. Ikiwa una usahihi mkubwa wa vipimo vya GPS katika (RTK) picha zako na unataka kutumia maelezo hayo pamoja na gcp faili, unaweza kutumia --force-gps.

Posti hii ina baadhi ya maelezo kuhusu kuweka Ground Control Target kabla ya flight, lakini tayari una picha, unaweza kiutafuta alama yako mwenyewe katika picha ulizonazo, unaweza kutafautisha eneo ambalo linapatikana ndani ya picha 3 angalau , na hapo utapata kiasi maeneo matano.

Pembe zenye ncha kali ni nzuri kuchagua kwa GCP. Pia unaweza kuweka/kutafuta GCP hata katika eneo lako la utafiti.

Faili la gcp_list.txt lazima litengenezwe wakati ukitengeza folder la project yako.

Kwa matokeo mazuri, faili lako liwe na mistari iziozidi 15 baada ya ufunguzi (point 5 pamoja na picha 3 kwa kila point).

interface ya mtumiaji

Unaweza kutumia moja kati ya interface mbili kutengeneza GCP faili:

• POSM GCPi

• GCP Editor Pro

POSM GCPi

POSM GCPi linabebwa na chaguo msingi la WebODM. Mfano unapatikana katika onesho la WebODM. Kutumia thamani hii ijulikanayo na udhibiti wa ardhi XYZ, Moja itafanya ifuatavyo:

Tengeneza idadi ya GCP ambazo zitakuwa na majina gcp (hii itaandikwa amabyo itaonekana katika kiwasilishi cha GCP),x,y,na z, pamoja na utangulizicha proj4 string ya GCP yako (hakikisha zipo katika mfumo wa ramani, kama UTM. Lazima ionekane ka hivi:

+proj=utm +zone=37 +south +ellps=WGS84 +datum=WGS84 +units=m +no_defs
gcp01 529356.250827686 9251137.5643209 8.465
gcp02 530203.125367657 9250140.80991621 15.781
gcp03 530292.136003818 9250745.02372435 11.977
gcp04 530203.125367657 9250140.80991621 15.781
gcp05 530292.136003818 9250745.02372435 11.977

Kisha inaweza pakia idadi ya GCP hii katika kiwasilishwa, pakia picha, na weka kila GCP katika picha.

GCP Editor Pro

Aplication nii inahitaji kuingizwa tofauti au inaweza kuingizwa kama WebODM plugin kutoka https://github.com/uav4geo/GCPEditorPro

Tengeneza CSV faili litalochukua jina la gcp, kaskazini, kusini na muinuko.

GCP Label,Northing,Easting,Elevation
gcp01,529356.250827686,9251137.5643209,8.465
gcp02,530203.125367657,9250140.80991621,15.781
...

Kisha ingiza CSV kutoka screen kuu na andika +proj=utm +zone=37 +south +ellps=WGS84 +datum=WGS84 +units=m +no_defs ndani ya sanduku la EPSG/PROJ.

Screen zifuatazo zitaonesha ramani kutoka sehemu na kuiita GCP kwa jina na kuita picha nyengine zilipo.

References

Toffanin, Piero. Open Drone Map: The Missing Guide. MasseranoLabs LLC, 2019.

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