WebImg
Command line: WebImg
Description: draw images
downloaded from online servers
TopoLT toolbar: 
Menu: TopoLT » Images » Draw images
from the Web
Using this
command you can draw images downloaded from online servers using the following
selection criteria:
1.
"Zone" - a rectangle selected
by two diagonally opposite points;
2.
"Polyline" - an existing polyline
in the drawing.
Note: The polyline can be pre-selected
before applying the command to avoid querying about the selected area.
The images are
downloaded from the servers defined in the "Connections"
table. A data request is sent to these servers using the URL address that is
coded specifically for these tasks and then a response is expected from the
server which can be in the form of a file with one of the JPEG, PNG or GIF
formats. The request for tiles with the images on a certain area is made using
the texts {x}, {y}, {z} or {q} as identifiers. The plates with the received
images are in the Mercator projection system and have dimensions of 256 x 256
pixels.
In the "Connections" table you can
enter the data about the servers you want to use to download images online. In
the "Saved file name"
column, you can enter the name of the file in which the image will be saved
when drawing it. If the filename is an empty string then the filename will be
the server name. The files are saved in the directory containing the DWG file
from which this command was called. If several images are drawn in the same
drawing, then the files will be numbered to avoid overwriting them.
The level of
detail can have a value between 0 and 23 and differs from server to server.
With the help of this parameter you can set the resolution of the images you
will download. Depending on this factor and the average latitude of the area,
the resolution of a pixel is calculated in meters per pixel.
A dot grid is
used to transform the image from the Mercator projection system to the local projection
system (the coordinate system of the drawing). The grid can have a cell size of
32, 64, 128 or 256 pixels. The points of this grid are calculated in both
coordinate systems and based on them the transformation of the image is applied
by the method "Affine and move
points", the description can be found in the Timg command.
Note: For very large areas it is
recommended to divide the area and draw several images, this way you will have a
better accuracy regarding the positioning of the pixels in the images.
To transform
points from the WGS84 (ETRS89) coordinate system to the local coordinate
system, a transformation model created with the TransLT application is
required. The accepted models are those that have as initial reference
coordinate system (CRS) a geographical coordinate system on the WGS84 (ETRS89)
ellipsoid with the
Note: To create a transformation model,
use the TransLT application where you can manually define your
transformation steps, or you can use the EPSG database to create a
transformation model between two coordinate reference systems (CRS). Also in TransLT
you can test the coordinate transformation.
In the drawing
options, you can choose the background color and the file format in which the
image will be saved.
When an area or a
polyline that has the shape of a rectangle is selected you can choose to create
ImageClip
on the selected rectangle for the image that will be drawn.
Note: To return to the previous
situation, use the Uimg
command or the Undo command of the CAD program. Using the Uimg command the downloaded image files will be
deleted.