Labwork for ESC 4511 Environmental Remote Sensing:
Question need to be answered
before we start using erMapper:
1. What
is rectifying process?
Simple words that
explain all is the process of converting/reassign coordinates to pixels from
few images into a one common plane. In details, rectification process is a
transformation process that used to project 2 or more images onto a image plane/
planimetric image. It’s also part of data projection that bring geometric
characteristics of data into conformance with a know coordinate system.
Rectification process correct any distortion by transforming the image into standard
coordinate system.
2. What
is GCP (Ground control point) in rectifying process
GCP are points
that greatly influence the accuracy of spatial interpolation of a data. GCP
normally are points on a paper or digital map that has known coordinates and is
used to transform another dataset. GCP serve the purpose of:
·
Digitizing data from from paper maps
·
Georeferencing both raster and vector data
·
Spatial adjustment operation
In short, GCP
stands for location that are identified on the raster dataset and in real-world
coordinates
3. What
is map projection
Map projection is
the process of expressing the 3D surface/ curved surface of the earth into a 2D
flat surface of a map. Map projection commonly and are important in creating
maps. However, it is not an easy job to project an 3D image onto a 2D surface
as distortion happens when doing so. Therefore, a good globe can provide
accurate representation of the earth and aid in map projection.
4. 4. What
is geodetic datum
Tools used to
define the size and size of the earth and the origin and orientation of the
coordinate systems used to map the earth
5. 5. Can
two maps of the different map projection can be overlap onto each other?
Provide reasons
Definitely yes.
As overlaying data layers from separate sources and coordinate systems can be
found in ArcGIS which enable us to intergrate datasets within maps that were in
common between map projections
6. 6. Number
of GCP we had utilized in georenferencing the aerial photos? Tables of our GCP
We used 6, for
the 125.alg
7. 7. What
are the criteria of a good GCP
If we are using
quadratic polynomial order in geocoding.
It requires minimum 6 GCP. But for a good result, we recommend 12 GCP. As for
the RMSE (root mean square area) must not be exceeding 1 for any of the points
8. 8. Provide
3 example of good features for GCP
·
Road intersection
·
Landmark like bridges or railway or buildings
·
Natural earth features like lagoons, bays or
estuaries
9.
9. What
is the min value of RMSE for each point that we manage to achieve
10. Why
do you think it is difficult to achieve the RMSE of less than 1 in this aerial
exercise
Because this
exercise requires absolute patients to plot the exactly points that have similar
coordinate with the correct one in the true location
1 11. Why
it is important to achieve RMSE of less than 1
In short, RMSE
estimate the goodness of the derived transformation. In this process, it
measures the fit between the true location and the transformed location of the
output control point. The smaller the RMSE, the more precise the point.
Aerial Photographs and Landslide Delineation
Study Area. shp:
Area of the polygon:
Latest update mosaic.tiff file
