GIS development essay (8)-a little understanding of GIS technology and mapnet control experiment

Today we will discuss a few things that are not closely related. If some people have their own unique insights on these issues or already know the technology, so please put it forward in your comments for discussion. Let's discuss it here ......
1. Over the past few days, I have been busy testing and modifying the GIS system. I have found some bugs and new requirements. This not only changes the style and layout of the interface, but also rarely changes the code, the map has the largest change and needs to be added to a raster map (terrible, a raster map actually has 1.3 GB). How can we load it? This GIS system is B/S structured and has many functions. In addition to raster graphs, it also has many layers of vector graphs and provides layer data and database data mutual query functions, so I am very worried that loading and displaying raster images will be very slow, or cause the server to crash. However, today I found that the raster images may still be loaded and displayed successfully. The details are as follows:
1. If you want to know whether raster graphs can be loaded, you need to understand the working principle of ArcIMS. We have discussed this in the first few articles in this series, the following is a brief description: The mapnet control interprets the ArcXML document returned by ArcIMS and loads the image generated by ArcIMS according to the request through a virtual path. The ArcIMS graphics service can generate image types: *. jpg, *. JPEG, *. PNG-8bit, *. PNG-24bit, *. GIF (requires a special serial number or registration file ).
2. It is precisely because of this working principle that, although the entire raster graph file is large, will ArcIMS process the size of the image file generated by itself, it will not generate an image file of G to be transmitted in the B/S program and network. After my own experiments, it is proved that ArcIMS does control the size of the transferred file. After adding a raster image, the image file is not as big as you think, so you do not need to cut the Raster image file, this makes me very happy. jpg and JPEG images with raster images and vector images are about kb in size, and PNG images with a size of about kb in this case. (The image size is for reference only)
2. Another problem is the mapnet control. The mapnet control has a function called myil to obtain layer data. recordset (myisq2, true, false, myigf). However, this function can load up to 2000 data records and generate a dataset, this means that the 0th tables in this dataset have a maximum of 2000 data records, but the mapnet control provides us with the object attribute myisq2.where, to query one or some elements on the required layer. SQL statements can be used in this attribute. The following is a piece of related code: