Digital Globe - data limit?

3dvr_m4

Different question. I'll try to explain as best I can.

The area I'm looking at is the Texcoco area in Mexico.

When I start to download data and then "Draw Box" for the area I'm interested in, and then select a large area around Texcoco, when the DigitalGlobe Data Access Options window opens, it only lists 1999 MDA EarthSat 15m data and downloads that to the area specified. (see Clipboard04.jpg below)

If I select a small area within the large area, the DG Access Options window shows 2007 DigitalGlobe 0.6m data.

The confusing thing is, if I select enough small areas to fill the original area (and then some) with small tiles, I am able to access the 2007 DG 0.6m data for the whole original area. I divided the area into 6 sections, and downloaded the free samples for each section individually. (see Clipboard02.jpg below)

I just have to do it in small chunks and not all at once.

Why? (or... Why can't I download the whole area at once?)

This is all via the "FREE Access to Watermarked Imagery for Reference Only" and not with the premium access number. I want to verify that the data exists first. Would I be able to download the whole area at one time with an access code?






TIA,
-3D

global_mapper

The problem with the list of available resources is that what DigitalGlobe reports as available is somewhat limited for very large areas. So when getting a large area only the sources appropriate for the initial zoom for that whole area relative to the screen size are reported as for large areas the total number of data sources for every resolution could be huge. When you get a smaller area the initial zoom would be of more detail, so better sources would be listed.

If rather than checking a particular source you just keep the default selection to 'Automatically Get Data from Best Available Source' you will automatically get the better sources as you zoom in on your data area.

Let me know if I can be of further assistance.

Thanks,

Mike
Global Mapper Support
support@globalmapper.com

3dvr_m4

It makes sense that the server would choose the appropriate data source based on screen size and requested area...in preview mode. For very large areas it appears to be choosing 1999 and smaller areas are 2007.

My question is, when we choose the very large area, and request it at very high resolution(1m) in export mode, will it download 1999 or 2007?

3dvr_m4

also... if the data says 0.6m ... and we want native resolution.

Do we enter 0.6 (for x) by 0.6 (y) or the square root of 0.6?

global_mapper

When you export the layer chosen will be the best one for the resolution of the export, so if you export at 0.6m resolution whatever the DigitalGlobe servers determine is the best match for that resolution will be chosen, unless of course you explicitly choose a source from the source list, in which case that will always be used.

If the stated resolution is 0.6m and you want full resolution, then use 0.6m for both the X and Y sample spacing when exporting.

Let me know if I can be of further assistance.

Thanks,

Mike
Global Mapper Support
support@globalmapper.com

3dvr_m4

What criteria is used to determine "the best one?"

In one area, it appeared to select a latter year, 2007 I believe, that had substantial cloud cover over a 2004 version that has almost no cloud cover.

TIA,
-3D

global_mapper

I believe that the highest resolution layer is given precedence, then the most current imagery is used if multiple images of the same resolution are found. Cloud cover does not come into play.

Thanks,

Mike
Global Mapper Support
support@globalmapper.com

3dvr_m4

The interface lists the following image as 0.6m data. We exported this small piece as:
0.6m x 0.6m, 0.5m x 0.5m, and 0.25m x 0.25m
The results are below...you can see the .25 looks better than the 0.6, which suggests that the data exported at 0.6 x 0.6 is not full resolution. How do we know what resolution to input if we want native resolution?

global_mapper

I think the main difference is not the actual resolution of the data, but the display artifacts that you don't see with a native 0.25m data until you zoom in further. If you enable anti-aliasing (interpolation) for the layers from the Options dialog from the Control Center, I think the visualization will be improved. I would also suggest turning that on for the DigitalGlobe layer prior to export.

Also note that when you export to a higher resolution more data tiles need to be downloaded for the same area, which can use up your download bucket significantly faster (i.e. twice the resolution is 4 times the data).

Let me know if I can be of further assistance.

Thanks,

Mike
Global Mapper Support
support@globalmapper.com