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 Greenwich prime meridian, and as final reference coordinate system (CRS), the coordinate system of the drawing from the CAD window. The model file or transformation models with MTR, MTRS or XML format as well as the grid files used, if applicable, will be added to the settings in the Configuration Transformations section using the TopoCfg command.

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. For the selected area or for a polyline that has the shape of a rectangle, you can 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.